Krypton - 85 in the Atmosphere: Accumulation, Biological Significance, and Control Technology (Ncrp Reports Ser. : 44)

NCRP REPORT No. 44

KRYPTON-85 IN THE ATMOSPHERE-AccumuIation, Biological Significance, and Control Technology

Recommendations of the NATIONAL COUNCIL O N RADIATION PROTECTION AND MEASUREMENTS

Issued July 1, ,1076 National Council on Radiation Protection and Measurements 7910 WOODMONT AVENUE/WASHINGTON, D.C. 20014

Copyright @ National Council on Radiation Protection and Measurements 1975 All rights resewed. This publication is protected by copyright. No part of this publication may be reproduced in any lform or by any means, including photocopying, or utilized by any informat~onstorage and retrieval system without wntten permission from the copyright owner, except for brief quotation in critical articles or reviews. Library of Congress Catalog Card Number 76-11458 International Standard Book Number 0-913392-26-x

Preface This report of the National Council on Radiation Protection and Measurements (NCRP), successor to the National Committee on Radiation Protection and Measurements, is concerned with the accumulation and biological significance of 86Krin the atmosphere, and the possible techniques available for its control. 8%r is relesased to the atmosphere through nuclear weapons tests and the generation of nuclear power. With the cessation, for the most part, of atmospheric testing of nuclear weapons, 86Krin the atmosphere results primarily from the reprocessing of nuclear fuel, very little s6Kr being released from the actual operation of the nuclear power plants themselves. This report estimates the future global concentrations of 85Kr in the atmosphere resulting from projected future levels of nuclear power use, the absorbed doses to man resulting from these concentrations, and possible techniques which may prove pract,icable for the future control of E6Kratmospheric levels. The present report was prepared by the Task Group on sSKr of the Council's Scientific Committee 38 on Waste Disposal. Serving on the Task Group during the preparation of this report were: MERRIL EISENBUD,Chairman Members

ROYE. ALBERT KENNETHCOWSER D. GOWBERQ EDWARD JOSEPHA. LIEBERMAN LESTERMACHTA C. UPTON ARTHUR

The Council wishes to express its appreciation to the members and consultants for the time and effort devoted to the preparation of this report. LAURISTONS. TAYLOR President, NCRP Washington, D.C. March 6, 1976

contents Preface . . . . . . . . . List of Tables . . . . . List of Figures . . . . . 1 Introduction . . .

.

...

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111

vii

...

Vlll

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1.1 General Remarks . . . . . . . . . . . . . . . . . . . . 1.2 Properties of Krypton and 86Kr . . . . . . . . . . . . 1.3 Sources of 86Kr . . . . . . . . . . . . . . . . . . . .

2

.

Estimates of Future Power Requirements. 86KrReleases and e6KrInventory . . . . . . . . . . . . . . . . . . 2.1 2.2

3

.

Future Power Requirements . . . . . . . . . 86Kr Generation and Inventory to the Year 2000

The Fate of

Discharged to the Atmosphere

3.1 The Oceans ns a Sink for 86Kr 3.2 Washout and Deposition of 86Kr 3.3 Atmospheric Dispersion of 86Kr

4

. Dosimetry 4.1 4.2 4.3 4.4 4.5 4.6

5

.

. . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . .

Dose from Photons Produced in a Semi-Infinite Cloud Dose from Bremsstrahlung Produced in Air or Skin . . Dose from 8bKrin the Body . . . . . . . . . . . . Dose from Beta Rays in an Infinite Cloud . . . . . . Dose from 8%r in the Airways of the Lungs . . . . Summary of Doses . . . . . . . . . . . . . . . .

Projected 86KrConcentrations

.. . .

. . . .

. . . .

. . . . . . . . . . . .

5.1 esKr Concentrations . . . . . . . . . . . . . . . . . . 5.2 Projected Population Dose Commitments . . . . . . . .

6

.

The Biological Significance of the Absorbed Dose . . . . 6.1 6.2 6.3 6.4

Genetic Effects . . . . . . . . . . . . . . . . . . . . Overall Carcinogenic Effects . . . . . . . . . . . . . . Carcinogenic Effects on Skin . . . . . . . . . . . . . . Possible Interaction of Ionizing and Ultraviolet Radiation .

1

~i 7

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CONTENTS

Status of 86KrRemoval from Waste Gases

. . . . . .

7.1 Adsorption a t Ambient Temperature . . . . . . . . . . 7.2 Cryogenic Adsorption . . . . . . . . . . . . . . . . 7.3 Cryogenic Distillation . . . . . . . . . . . . . . . .

7.4 Selective Absorption . . . . . . . . . . . . . . . . . . 7.5 Permelective Membranes . . . . . . . . . . . . . . 7.6 Clathrate Precipitation . . . . . . . . . . . . . . . .

.

8 Discussion . . . . . . . . . . . . . . . . . . . . . . 9 . Summary . . . . . . . . . . . . . . . . . . . . . . APPENDIX A . Calculation of Long-Term Air Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . APPENDIX B . Phantom Description . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . The NCRP . . . . . . . . . . . . . . . . . . . . . . . . NCRP Reports . . . . . . . . . . . . . . . . . . . . . . . Index

. . . . . . . . . . . . . . . . . . . . . . . . . .

40

List of Tables 1. Primary radiations from 8bKrdeca,y . . . . . . . . . . . . 2. Secondary radiations from s6Kr decay .. .. . . .. . . 3. Projections of annual electric energy generation in the United States . . . . . . . . . . . . . . . . . . . . . . . . 4. Cumulative installed nuclear electric power capacity in the United States . . . . . . . . . . . . . . . . . . . . 5 . Projection of electric power generating capacity in the world. . 6. Cumulative installed nuclear electric power capacity in the world . . . . . . . . . . . . . . . . . . . . . . . . 7. Assumed nuclear reactor mix and world accumulation of s6Kr in year 2000 . . . . .. .. . . .. .. . . .. .. 8. Estimated production and accumulation of 86Krin world nuclear power economy . . .. .. . . . . .. .. .. 9. The oceans as a sink for S6Kr . , , . , . . . . . . . . . 10. World population weighted concentration from uniform release rate of 1 curie of 85Krin 1 year . . . . . . . . . . . . 11. Percentage of separable adipose tissue and nonfat tissues and the Ostwald coefficient for subdivisions of the human body. . 12. Equilibrium absorbed dose rate to body organs per unit air concentration from immersion in a semi-infinite cloud of 86Kr . . . . . . . . . . . . . . . . . . . . . . . . 13. Comparison of equilibrium absorbed dose rates to body organs per unit air concentra.tion from immersion in a semi-infinite cloud of 8bKr . . . . . . . . . . . . . . . . . . . . 14. Estimated world population dose commitments from annual worldwide reIeases . . . . . . . . . . . . . . . . 15. Several processes available for 85Kr off-gas treatment . . . . .. . . A-1. Phase 4 average surface air concentration of 86Kr

vii

List of Figures 1. Decay scheme of 86Kr . . . . . . . . . . . . . . . . . . 2. Atmospheric 86Kr concentratio~lsfrom weapons testing and . . . . . . . . . . . . . . . . plutonium production 3. Energy spectrum for scattered photons . . . . . . . . . . 4. Depth dose in tissue from beta radiation . . . . . . . . . . 5 . Concentration of 86Kr measured in northern hemisphere air samples . . . . . . . . . . . . . . . . . . . . . . 6. Predicted average concentrations and annual skin dose equivalent rates due to 86Krin the atmosphere . . . . . . . . A-1. Mean annual surface air concentration contours (10-20 Ci/ma) for the release of 1 Ci/y of 86Kra t Morris, Illinois (Phase 1) . . . . . . . . . . . . . . . . . . . . A-2. Mean annual surface air concentration contours Ci/m3) from Phase 2 . . . . . . . . . . . . . . . . A-3. Mean annual surface air concentration contours Ci/m3) from Phase 3 . . . . . . . . . . . . . . . . . . . . . . . . . . B-1. Legs and male genitalia of phantom

viii

1. Introduction 1.1 General Remarks The projected rapid growth of the nuclear power industry necessitates a careful assessment of any related potential for environmental pollution. 86Krreleases deserve special attention because of the inherent difficulty in their control and their essentially nonreactive and mobile nature in the atmosphere. The purpose of the present report is to estimate the future global concentrations of 86Kr, their potential significance, and possible techniques for their control. Projections of SGKraccumulations will be made to the year 2000, as this is now sufficiently close to permit reasonable approximations to be made of the world's energy requirements and the extent tro which they will then be fulfilled by nuclear power reactors. On the other hand, the year 2000 is sufficiently far off to allow for periodic reappraisal of the projections of 86Kr accumulation in relation to developing information about the biological effects of this nuclide and the technology for control of 86Krreleases. In addition to the global projections, the present report also includes estimates of S6Kr concentrations near nuclear fuel chemical reprocessing plants. Problems associated with S6Krdisposal have been previously reviewed by Kirk (1972), Dunster and Warner (1970), Coleman and Liberace (1966), Diethorn and Stockho (1972), Karol et al. (1971), and Bryant and Jones (1973).

1.2 Properties of Krypton and 86Kr 1.2.1 Chemical Properties.

Krypton is one of the class of noble gases which includeshelium, neon, argon, krypton, xenon, and radon. These are colorless, tasteless, and in general, chemically inert. I n recent years, however, they have been shown to be capable of entering into ionic or covalent bonding with highly reactive elements such as fluorine or oxygen. Bartlett (1962) reported a chemical reaction between xenon and HE' yielding XeF4.The first report 1

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INTRODUCTION

of a chemical rewtion involving krypton came from Grome et al. (1963), who reported the production of KrF, from a mixture of krypton and fluorine through which an electric discharge had been passed a t 86OK. Later work, however, indicated that the resultant compound was K r F z (Schreiner et al., 1965), a white crystalline solid which sublimes a t temperatures well below 273"K, but which can be stored for several weeks a t dry ice temperature (195'K) without appreciable loss. Recently, the crystal structure of KrFa has been investigated by low temperature x-ray diffraction techniques (Burbank et ad., 1972). Noble gases, including krypton, have been shown to enter into compounds called clathrates (Lindquist and Diethorn, 1968; M c C l a i and Diethorn, 1964; Balek, 1970; Chernick, 1967) in which the noble gas atoms are physically entrapped in molecular cages of hydroquinone, or other organic compounds. In addition, the noble gases have been shown to be highly soluble in nonpolar solvents (Steinberg and Manowitz, 1958) with this solubility increasing with decreasing temperature (Nichols and Binford, 1971). The solubilities of the various noble gases are related as Rn > Xe > Kr > Ar > Ne > He.

1.2.2 Physical Data. The Handbook of Chemistry and Physics (Wesst and Selby, 1971) and C~:ryogenic Reference D d a (Union Carbide Corp., 1967) give the following values for physical constants of krypton: Atomic number = 36 Atomic weight (naturally occurring) = 83.80 Melting point = - 156.6'C (116.6"K) Boiling point = - 152.30 & 0.1O0C (120.85 f 0. 10°K) Triple point = - 157.Z°C, 548.2 mm Hg (116.0°K, 73.09 kPa) Critical point = - 63.8OC, 4.12 X lo4mm Hg (209.4'K, 5.49 MPa) Density = 3.733 g/l
1.2 PROPERTIES OF KRYPTON AND 8bKr

1.2.3

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3

Racliologieal Properties.

has a half-life of 10.7 years; its decay scheme is rather simple, in that only two beta rays and a single gamma photon are emitted. The decay scheme, as given in Martin (1973), is shown in Fig. 1. Table I gives information on the primary decay products, while Table 2 gives

Fig. 1. Decay scheme of 86Kr (Martin, 1973).

TABLE1-Prima~y radiations from 'KT decayh,b ~ ~ d i . ~ Mean i ~ ~N* Pm Decay

Endpoint Energy0 (MeV)

Martin (1973). These values are slightly higher than earlier reported values (Lederer et al., 1968) for the endpoint energies of 81- and BI- of 0.16 and 0.672, respectively (mean energies of 0.0437 and 0.251 MeV, respectively). These earlier values are the one8 used in Chapter 4. Mean energies of 81-and 0%-are 0.0475 + 00.0006 and 0.251 1 0.008, respectively.

TABLE 2-Secodary radiations from &KTdecay Radiation

Mean Number Per Decay

Energy (MeV)

0.00003 O.OOOO1 0.00004 0.00008

0.49880 0.01340 0.00139 0.00024

- -

Shell converaion electron &,x ray L , Auger electron Mxy Auger electron

/

4

INTRODUCTION

information on the secondary decay products as obtained by the methods of Dillman (1969). Fission yields for 85Krha.ve been estimated in the literature and are given below in mean yield per fission event:

Yi (2S6U,thermal.neutrons)

= 0.00293 (Katcoff, 1960); 0.00273 (Katcoff and Rubinson, 1965); 0.0029 (Meek and Rider, 1968); 0.0034 (Nichols and Binford, 1971) Y i (2S6U,fission neutrons) = 0.0032 (Meek and Rider, 1968) Yi (236U,fast neutrons) = 0.0034 (Nichols and Binford, 1971) Yi (2a9Pu,thermal neutrons) = 0.00099 (Katcoff and Rubiison, 1965); 0.0014 (Meek and Rider, 1968); 0.0014 (Nichols and Binford, 1971) Yi (2a9Pu,fission neutrons) = 0.0014 (Meek and Rider, 1968) Yi (2a9Pu,fast neutrons) = 0.00076 (Burris and Dillon, 1957); 0.0017 (Nichols and Binford, 1971) Yi (2a3U,thermal neutrons) = 0.0055 (Katcoff,1960) Y i (23W,fission neutrons) = 0.0017 (Nichols and Binford, 1971)

1.2.4

Biological Prqerties.

Being chemically inert, krypton and other inert gases are not usually involved in biological processes. They are, however, absorbed into the tissues of the body via inhalation and dissolution in body fluids and tissues. Xenon has been shown to combine with specific sites within certain protein molecules and the binding sites have been identified by x-ray diffraction studies (Featherstone el al., 1975). Krypton is characterized by low blood solubility, high lipid solubility, and rapid diffusion in tissue (Kirk, 1972), (see Section 4.3). Exceptions to the biologically inert characterization of inert gases have been noted by numerous studies and have been listed (Kirk, 1972). Among these are an anesthetic action of xenon in humans (Balek, 1970; Cullen and Gross, 1951); a radioprotective action by inert gases in animals (Schreiner, 1963) and bean sprouts (Featherstone and Muehlbaecker, 1963). These phenomena are not generally understood, but have been postulated to depend on membrane effects involving lipid solubility or stabilization of the formation of hydrate microcrystals in the nervous system to block electrical conduction (Kirk, 1972; Featherstone and Muehlbaecker, 1963; Pauling, 1961). A comparatively high uptake of krypton by the adrenal gland has been reported (Featherstone and Muehlbaecker, 1963) but can be interpreted in the light of more recent work as a transient phenomenon resulting from the short exposure times employed (Kirk, 1974).

1.3 SOURCES O F s m r

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5

1.3 Sources of E6Kr

1.3.1 Natural Sources. is present to a small degree in the natural environment due to the mechanisms of spontaneous and neutron-induced fissions of natural uranium and due to neutron capture reactions from cosmic ray neutrons interacting with atmospheric 84Kr.Diethorn and Stockho (1972) have recently discussed the expected steady-state environnental inventories of S6Kr from these sources. They calculated equilibrium 85Kr activities, due to spontaneous fission, of approximately 2 Ci (of natural uranium) in the upper 3 meters of the t ~ t a land l and water surface. Neutron-induced fissions were found to contribute equilibrium activities of about Ci in the oceans. The equilibrium activity of atmospheric due to cosmic ray neutrons was calculated to be about 10 Ci. These estimates serve as interesting comparisons with estimates of man-made sources of 86Krthat will follow, but are negligible in any total analysis of the world's total 86Krinventory. 1.3.2 ATuclear Weapons Testing and Production of S6Kr. Since 86Kris produced during fission, it has been generated by nuclear weapons. tests An estimate of the specific yield of 85Kr per megaton1 (MT) of nuclear fission can be obtained from the 236Uyield of 86Krfor fission neutrons of 0.0032 given above, and from the fact that the complete fission of about 56 kg of material will produce a 1 M T yield. These numbers, coupled with the historical record of atmospheric test,s, as estimated by the Federal Radiation Council (1963), result in an estimate of the integrated 86Krgeneration, between 1945 and 1962, of approximately 5 MCi, and a current inventory, from these tests, of approximately 2 MCi. Assuming uniform dilution in an atmosphere of 5.14 X lW1 g, with a sea level density of 1.293 X 10-"/cm3, the current 86Kr inventory can be converted to a concentration of 0.5 pCi/ma, in agreement with a similar calculation by Diethorn and Stockho (1972). An uncertainty exists in these calculations became of the unknown (classifiedT ratio of 23sUand 236Uin the exploded devices. A one megaton (MT) nuclear or thermonuclear explosion, or "a megaton of nuclear fission," is an explosion which releases energy equivalent to that from one MT of TNT.

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6

INTRODUCTION

The production of plutonium for use in weapons has also contributed to the worldwide inventory of 86Kr. In the U.S., this activity has taken place mainly in the Hanford and Savannah River plutonium production reactors, the power levels of which have been classified through most of their histories, as have similar data on the production reactors of other nations. However, using fragmentary data from the AEC and assuming all 86Krproduced is released to the atmosphere, Diethorn and Stockho (1972) have estimated the 86Kr generation from the U.S. plutonium production. Their results, shown in Fig. 2, along with the assumed power levels of production reactors and 86Kr concentrations from weapons tests, indicate that production in reactors has generally accounted for higher 8bKrconcentrations than weapons tests. The release of 86Krin underground weapon tests, not included here, is minimal. I t has been estimated that United States plutonium production reactors contributed about 15 MCi as of 1966 (Bernhardt et al., 1975). These production figures are to be seen as lower limits due to the failure to include the plutonium production contributions from nations other than the U.S. I t will be seen later that this worldwide production of plutonium for weapons is rela70

9

Total = 203 megatons

C

1955

1955 '"r

75 YEAR Weapon test history

65

65

75

1985

1945 50

55

60

65

70

75 1980

YEAR

Assumed pluton~umproduction reactor operating h~story

1985

YEAR from fission weapons tests

1945 55

66

75

85

95

YEAR 06Kr from plutonium production reacfors at Hanford and Savannah River plants

Fig. 2. Atmospheric 8% concentrations, at standard temperature and pressure, from weapons testing and plutonium'production. (Diethorn and Stockho, 1972). [Modified from HEALTH PHYSICS 23, 653 (1972), which was used by permission of the Health Physics Society.]

1.3 SOURCES OF E6Kr

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7

tively small in comparison t s prospective future generation of 86Krby the nuclear power industry. 13.3 Power Reactors and Reprocessing Plants. 86Kris produced in a typical low-enrichment, light-water power reactor (LmPR) a t the annual rate of 0.75 kg/1000 MW of electric power (USAEC, 1970a). For a 1000 MW electric power reactor, the average annual production rate is 300 Ci/MW of electric power. This 86Kris formed by the fission process in the fuel elements where it is retained until the fuel element is reprocessed. Only the very small fraction (<1%) of the noble gases leaking through the fuel cladding is released during reactor operations. For this reason, the 8bKrreleases from normally operating reactors are insignificant compared to the releases from fuel reprocessing plants. Thus, Kahn et al. (1971) reported the release rate of 83Krfrom Dresden I, a 210 M W electric power boiling water reactor (BWR), to be 0.12 pCi/s. This is equivalent to 1.9 Ci/y, assuming a 50 percent load factor. We have seen earlier that 86Kris produced at an annual rate of 300 Ci per MW of electric power, or at a rate of 300 X 210 = 6.30 X lo4 Ci/y in Dresden I. The release rate was thus 1.9/6.3 X lo4, equal to 3 X 1W6 of the rate of *%r production. Future BWRJs can be expected to release less than this, since Dresden I was one of the first commercial nuclear power plants, and began operation in 1960. Pressurized water reactors of contemporary design have been reported to release less s6Kr than the value given above (Logsdon, 1972). The irradiated fuel from light water reactors is stored intact for a t least 150 days, and at some subsequent time is reprocessed, resulting in the release of the bulk of the noble gas fission products (of which 8SKr is the only significant isotope remaining) to the atmosphere (Nichols and Binford, 1971). Operations at the Nuclear Fuel Services reprocessing plant in New York have been estimated to release approximately 5000 Ci of 8bKrper batch of fuel, where each batch weighs about 1ton2 (Kahn et al., 1971). It is estimated that the fuel reprocessing plant of AlliedGulf Nuclear Services a t Barnwell, South Carolina, will release 8bKrat the rate of 1.6 X lo7 Ci/y (USAEC, 1974). The quantities of 8 b K r released to the atmosphere each year by the nuclear power industry will, in the absence of emission controls, be determined by the size of the operating nuclear generating industry, by 1 The Nuclear Fuel Services plant was built with a capacity of 300 metric ton units (MTU) per year, but is currently being expanded to a capacity of 900 MTU/ year.

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INTRODUCTION

the amount of fuel reprocessed, and, because of the variability of fission yields for different types of reactors, by the reactor "mix." The 1970 installed nuclear power capacity, excluding China, has been estimated a t approximately 24,000 MW of electric power (Spinrad, 1971). Assuming that this capacity operated a t an average load factor of 50 percent, a rough estimate of ubKrgeneration in that year is 3.6 MCi, or about 70 percent of the quantity released by nuclear weapons tests from 1945 to 1962. The increasing use of nuclear power reactors will necessarily result in large increases in B5Kr generation with time. More precise estimates of future inventories from this source are discussed in Section 2. Naval propulsion reactors also contribute to the inventory of 86Kr. Although not much information is available, it has been estimated that the inventory from this source was about 3 MCi in 1970. This will continue to rise, but will probably not be important in relation to power reactors (Bernhardt et al., 1975). 1.3.4 Peaceful Uses of Nuclear Explosives.

An additional source of potential u6Krexposure may exist in the future due to the utilization of nuclear explosives for peaceful purposes. I n the United States this program is known as "Project Plowshare." I t has been suggested that nuclear explosives could be of use in large-scale excavation projects and in the stimulation of oil and gas reservoirs. The production of 8Wr from these sources should be relatively small as compared to the production from the high yield nuclear weapons tested in the 19601s,or from the nuclear power industry, simply because of the small size of the explosives that would be employed and the low ratio of fission to fusion in Plowshare devices. The potential radiological impact from radioactively contaminated natural gas has been considered recently by Jacobs et al. (1972) and Barton et al. (1971) in light of data generated by the Gasbuggy and Rulison tests. Barton and coworkers estimated total 85Krgeneration from these test explosions of 370 and 960 Ci, respectively, fairly insignificant amounts when compared to the 86Krgenerated by nuclear power reactors. However, the total amount generated by an active Plowshare program could be much larger, depending on the scale of the program. Rubin et al. (1972) estimated that the detonation of 370 explosives per year for gas well stimulation would result in a steady state release of 86Kramounting to 0.85 MCi/y and that worldwide buildup of 85Krfrom t h k source would rise to 13 MCi. Exposure to the public from stimulation of natural gas by nuclear explosion might occur in the vicinity of a natural gas processing plant or within a community using natural gas for home or central power gen-

1.3 SOURCES OF

86Kr

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9

erating purposes. Barton et al. (1971) and Jacobs et al. (1972) both regard tritium exposure as being more important in such situations than exposure. For tritium at a concentration of 1 pCi/cms, Jacobs et al. (1972) calculated a maximum exposure of 2.5 mrem/y with an average exposure of 0.50 mrem/y, where these numbers reflect natural gas use patterns in the Los Angeles basin and the San Francisco Bay area.

2.

Estimates of Future Power Requirements, "Kr Releases and "Kr Inventory

Any long-term projection of fission product sources from a world civilian power economy is speculative at; best. There are a number of factors that may influence the definition of these potential sources including: population growth and energy consumption per capita; availability of natural resources; energy requirements to be met by central generating stations; nuclear power contribution to electricity production; the kinds of reactors to be used; nuclear fuel irradiat.ion time, and irradiated fuel cooling time; and the radwaste systems to be used in the nuclear fuel cycle. I n this section of the report, the various projections required to estimate future 86Krgeneration have been summarized. Such projections may provide insight into possible problem areas (or lack thereof), but they should be recognized m only best estimates within the context of a rapidly developing technology. It is recognized that an analysis of error associated with these estimates is an important topic for future consideration, since uncertainty in each parameter precludes a precise dehition of the source strength.

2.1 Future Power Requirements

The following subsections include a summary of various projections of energy consumption and electrical generation capacity (including nuclear) both in the United States and in the world. Their inclusion provides a framework within which projections are made of the 8%r source strength. 10

2.1 FUTURE POWER REQUIFtEMENTS

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11

TABLEI 3-Projection of annual electric energy generation (106 GW h) in the United States" Year

Law

Median

Wb

USAEC, 1962; USAEC, 1967a; Thompson, 1971; USAEC, 1970c. b Parenthetical values from USAEC, 1967a and USAEC, 1970c when they differ from those in Thompson, 1971. Same values listed in Shaw, 1969.

2.1.1

Uniled Slates Energy Req~irernenk.~

Table 3 lists projections of annual electric energy generation for the years 1980, 1990, and 2000 with low, median, and high values given (USAEC, 1967a,; Thompson, 1971; USAEC, 1970c; Shaw, 1969). The most recent projections by Whitman el a2. (1972) list annual central station electric energy generation in the year 2000, in units of million GWsh, as 8 low, 10 probable, and 12 high. Many projections have been made of the total electric power capacity of nuclear power plants likely to be installed in the future (USAEC, 1962; USAEC, 1967a; Thompson, 1971; USAEC, 1970c; Shaw, 1969; Whitmsn et al., 1972; USAEC, 196713; ORNL, 1970; Nichols and Binford, 1971; USAEC, 1971). Those listed in Table 4 were made a t different times in the past, and they are found to increase as the data of projection becomes more recent, reflecting positive economic factors, generally good operational experiences, advances in technology, and uncertainties in regard to the long-term availability of fossil fuels. These data are in reasonable agreement with more recent data given by Chitwood (1975). Approximately 1000 GW of installed nuclear electric power is indicated by the year 2000 in the United States. 2.1.2

World Energy Requirements.

The projection of energy requirements in the world and sources to satisfy these requirements are subject to perhaps even greater uncertainty (i.e., economics, energy supply policies, international po1it.i~~) a The estimates given here are baaed on data that was available before the MidEast war of 1973. The energy crisis that has since developed will undoubtedly alter the assumptions used. However, the differences will not be sufficient to change the conclusions in this report.

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2. ESTIMATES OF FUTURE POWER REQUIREMENTS

TABLE4--Cumulative instalkd nuclear electric power capacilg (GW)i n the United Slates Year and Source of Projection

1962 USAECa 1964 USAECb 1966 USAECo 1967 USAECd 1969 USAECe 1970 ORNLf 1970 USAECg 1970 USAECh 1971 ORNL' 1971 USAECj

Installed Nuclear Electric Power Capacity 1970

1980

5 6.5 10 10

40 75 95 145 150 153 150 124-171 149 150

14 6.1 5

1990

2000

734

389 481

941 735 950 484-1155 1294

a USAEC, 196713. In Table 3 of this reference, values referred to as midpoint of range with original source in Table 16 of Appendix IV of Cavilian Nuclear Power (USAEC, 1962). b USAEC, 1967b. In Table 3 of this reference, values referred to as midpoint of range with original source in Estimalad Growlh of Civilian Nuclear P o w e ~(USAEC, 1966). USAEC, 1967b. I n Table 3 of this reference, values referred to as midpoint of range with original source in p. 6 of AEC press release S-20-66, of June 7, 1866, and in Table 1of AEC press release 5-23-66, of September 8,1966. d USAEC, 1967b. In Table 3 of this reference, values referred to as midpoint of range with original source in AEC news release K-132 of May 31, 1967. Shaw, 1969. Fig. 1. f ORNL, 1970. Table 2.1. g Thompson, 1971. Table 1. b USAEC, 1970~. I n Table 6.2, the low values are for Case 2-A in which fossil and light water reactor (LWR) plants are considered and the high values are for Case 2-F in which fossil, LWR, high temperature gas reactors (HTGR) and liquid metal fast breeder reactor (LMFBR) plants are considered. i Nichols and Binford, 1971. Table 2. j USAEC, 1971. Table 4.

than in the United States. Spinrad (1971) has subdivided the world into various regions and has projected the electric power needs and nuclear electric power growth in each region to the year 2000. These are 1isi;ed in Tables 5 and 6. He acknowledges the difficulty in making long-term projections, and considers those beyond 1985 to be of a speculative nature. Several earlier estimates have been made of nuclear power growth in the world. Coleman and Liberace (1966) estimated nuclear thermal power capacity (presumably generating) in the year 2000 of about 3300 to 5000 G W , h h i c h at 36 percent thermal efficiency is about 1200 to 1800 GW Taken from Fig. 2, Coleman and Liberace (1966).

2.1 FUTURE POWER RXQUIREMENTS

TABLE &Projection Africa

/

13

of electric power generating capacity (GW) i n the worlds ~ a t i ? Eastern

America Europe

No* Western Amenca Europe

USSR

Spinrad, 1971. Excluding mainland China. Turkey included with Eastern Europe. d Australia, Japan, New Zealand, South Africa.

a

b

TABLE &Ci~mulalive installed nuclear electric power capacity (GW) i n the wwlda Year

Africa

Latin America

Eastern Europe

North America

Western Europe

USSR

otherd

~ ~ t ~ l b

Spinrad, 1971. Excluding Mainland China. Turkey included with Eastern Europe. d Australia, Japan, New Zealand, South Africa.

a

of electric power. A report by the United States Atomic Energy Commission (USAEC, 1965) lists a free world installed nuclear electric power capacity of 122 GW to 184 GW in 1980; a value of 1468 GW was estimated for the free world in year 2000 by assuming that foreign installed nuclear electric power capacity equalled the projected United States nuclear electric power capacity of 734 GW (Thompson, 1971). In a later report by the USAEC (1971), the free world installed nuclear electric power capacity is estimated at 277 GW in 1980. The world estimates of Spinrad (1971), shown in Tablo 6, do not include mainland China. Nichols and Binford (1971) take account of this fact by increasing the nuclear electric power projection for Asia in proportion to 1970 populations (from 1070 to 1815 million people-a factor of 1.68). Their world projections of installed nuclear electric power capacity are aa follows: 24 GW in 1970; 353 GW in 1980; 1660 GW in 1990; and 4500 GW in 2000. These values are only somewhat larger than those in Table 6. I t is relevant to note that the vast majority of instalIed nuclear power will be in the northern hemisphere.

14

/

2. ESTIMATES OF FUTURE POWER REQUIREMENTS

2.2

86KrGeneration and Inventory t o the year 2000

Several estimates have been made of the quantity of * K r produced and accumulated by the world nuclear power generating capacity in the year 2000; these are listed in Table 7. Those of Coleman and Liberace (1966) are based on a world nuclear electric power capacity (presumably generating) of 1200 to 1800 GW and a reactor mix consisting of thermal burners, thermal converters, and fast breeders. They provide informaTABLE 7-Assumed nuclear reactor m i x and world accumulalion o f =KTin year 2000 Nichols and Binfordb

Coleman and Libera&

Electric Power (GW) Thermal Power (GW) Light Water and Other Thermal Reactors Percent of Nuclear Generating Capacity Percent Yield of "Kr: '3&U (Thermal Neutrons) a38U(Fission Neutrons) 230Pu (Thermal Neutrons) Fast Breeder Reactor Percent of Nucleai- Generating Capacity Percent of a6Kr: 236U(Fast Neutrons) 2aaU(Fission Neutrons) ~ P (Fast u Neutrons) 240Pu,a41Pu(Fast Neutrons) T h r m a l Converler Reactor Percent of Nuclear Generating Capacity Percent Yield of 28aU (Thermal Neutrone) S6Kr Produced Annually (MCi) a6Kr Accumulated (MCi) Coleman and Liberace, 1966. Nichols and Binford, 1971. TABLE8-Estimated production and accumulatwn of WKr in world nuclear power economys

World Nuclear Electric Power (GW) Annual Production B5Kr (MCi) Total Accumulated u6Kr (MCi) Nichols and Binford, 1971.

21 6.5 55

353 103 339

1660 461 2070

4500 988 6280

2.2

86Kr

GENERATION AND LNVENTORY TO THE YEAR 2000

/

15

tion on the fraction of pourer assumed to be contributed by each type of reactor and on the yield of 85Kr.Nichols and Binford (1971) base their projections on an installed world nuclear electric pourer capacity of 4500 GW. They assume a reactor mix consisting of light-water reactors and liquid metal fast breeder reactors (LMFBR's). The nuclear characteristics of the Diablo Canyon Nuclear Power Plant (burnup of 33,000 MW.days per metric ton and specific power of 30 MW per metric ton) and the Atomics International Reference Oxide LME'BR (proportionally mixed core and blanket with burnup in excess of 30,000 MW-days per metric ton and specific power of 58 MW per metric ton) were assun~ed for use as reference light-water and fast-breeder reactors, respectively (ORNL, 1970). Although the assumptions used in these two studies are different, the projected accumulations of 86Kr agree within a factor of 2. For the purpose of this study, the projections of Nichols and Binford (listed in Table 8) are chosen as the basis for analyses because their projections are based on more recent information of likely power requirements and reactor types to be used in the future, and also yield slightly larger results than those of Coleman and Liberate, providing a more conservative basis for 86Kr concentration projections.

3.

The Fate of "Kr Discharged to the Atmosphere

8aKrdischarged to the environment will disperse in the atmosphere and in other receiving bodies, such as the oceans and continents. The present section will discuss the environmental dispersal of 86Krand will project its concentration in the atmosphere to the year 2000.

3.1 The Oceans as a Sink for 8K.Kr

The eficiency of the oceans as a sink for 8bKr can be determined by examining the natural krypton contents of the atmosphere, the mixed layer of the ocean, and the total ocean. The relative amounts of krypton in these bodies will give an idea of the efficiency of the ocean as a l q p t o n sink, with any arguments generated in this manner easily extendible to 86Krthrough specific activities. A krypton concentration value of 1.113 X 1 P by volume of air has been reported recently (Keller, 1973). Using an atmospheric volume of 3.96 X loz4cmBat standard temperature and pressure (STP),and a deng/cm3, a total mass of 1.64 X l(Y6 g sity of krypton of 3.73 X krypton in the atmosphere is obtained. This can be compared with the amount of krypton in the mixed layer of the ocean by assuming that this layer extends down to 100 meters from the surface of the ocean, using the measured average krypton concentration value of 5 X lov8by volume in this layer of seawater (Bieri et al., 1966), and assuming a total ocean area of 3.6 X 1018 cm2. The result is a total mass of 6.7 X 1(Y2 g of krypton in the mixed layer of the ocean, or approximately 0.04 percent of the atmospheric mass of krypton. Similarly, the total mass of krypton in the oceans as a whole can be compared with the total atmospheric mass of krypton by using an average concentration by vol(Bieri et al., 1966), a total ume for krypton in the oceans of 9 X ocean volume of 1.4 X lP4cma, and a krypton density of 3.73 X g/cma at STP. This calculation results in a total ocean inventory of about 4.7 X 1014 g of krypton, or approximately 3 percent of the at16

3.2 WASHOUT AND DEPOSITION OF

/

17

TABLE 9-The oceans as a sink for UKra Medium

Atmosphere Mixed layer of the oceans (top 100 m) Oceans as a whole

Total Mass ol Krypton (9)

Percent oi Atmospheric Krypton

1.64 X 1018 6.7 X 10l2 4.7 X 1014

100.0 0.04 3.0

in the Medium

a Modified from Bieri et al., 1966. (Copyright held by American Geophysical Union. )

mospheric total. It should be noted that the average concentration of krypton in the oceans as proposed by Bieri et al. is similar to the value found by Hinterberger et al. (1964). These amounts of krypton and their corresponding percentages of the atmospheric total are summarized in Table 9. Clearly, the percentage which these numbers represent, relative to the atmospheric burden, indicate that the oceans, on the basis of any model's predictions, will be a trivial sink for the 86Krdischarged into the atmosphere.

3.2

Washout and Deposition of s6Kr

Tadmor (1973) has recently estimated the atmospheric deposition parameters for S6Kr, including those describing washout, dry deposition, and deposition through adsorption on particulate matter. In general, he h d s that these processes can act as a sink for only small portions of the total radioactive gas because of competition from the natural krypton in the atmosphere. I n considering washout of Tadmor assumes that the low solubility of krypton gas in water (1.85 X lWOa t equilibrium) will limit its sorption in rainwater, while the solubility of will be simultaneously limited by the much greater abundance of stable krypton. In the environs of a 10 ton/day reprocessing plant releasing 1 Ci/s of 85Krfrom a 100 m stack, the maximum concentration of S6Kr for average atmosg/m3 (Tadmor and Cowser, 1967), pheric conditions will be 2 X which is about six orders of magnitude less than that of stable krypton in the atmosphere. Using these numbers and an average rainfall figure of about 4 mm/h, Tadmor (1973) arrives a t a washout coefficient of A, = 4 X 10-l1 s-I. This would result in a negligible depletion of 86Kreven from a relatively concentrated cloud, such as was assumed. This phenomenon can be ignored in atmospheric dispersion calculations. The maximum amount of 85Kr which can be deposited on the soil via

18

/

3. THE FATE OF

86Kr

DISCHARGED TO THE ATMOSPHERE

dry deposition will occur if the interaction process between the soil and krypton is irreversible, in which case the flux to the surface would be independent of the amount already deposited there. However, there are indications that the soil-krypton interaction is not irreversible. The limiting capacity has been estimated to be about 9 X 10-0 g krypton/g mantle rock. If one assumes that the natural capacity of the mantle rock for krypton is 9 X 10-lo g krypton/g mantle rock and that diffusional penetration of 85Kroccurs uniformly throughout its radioactive life, an effective diffusion coefficient of 0.05 cm2/s would l e d to an estimated mean penetration of s % ~to a depth of about 60 m and a quantity of stable krypton for mixing of about 8 X 1012 g. This is about 0.05 percent of the total krypton in the atmosphere. The apparent deposition velocity of BKr to maintain steady state would be about 3 X lWBm/s. Long term studies estimate transfer velocities of 85Krto vegetation to be in the range of 10-lo to leg cm/s (Voilleqbe and Fix, 1975). Even if a deposition velocity as high as cmjs is assumed to be representative for terrestrial ecosyst.ems, and it is assumed that all transferred krypton is eventually deposited in the mantle rock t o a depth of 60 m, this would be equivalent to a loading of 3 X 10-la g krypton/g mantle rock and an effective sink for krypton equivalent of 2.7 X logg krypton. This is about 1.6 X 1W6 percent of the mass of krypton in the atmosphere. Tadmor (1973) suggests that the amounts of 86Kr absorbed by the soil a t equilibrium would be directly proportional to t.he ratio of radioactive and stable krypton in the atmosphere. This assumes complete exchange between the krypton absorbed in the ground and that in the air. Under this assumption, and since the concentration of stable krypton is about lo6 times that of 86Kr,under the conditions given above it is obvious that the mantle rock is of no importance as a sink for 8bKr. A final form of deposition considered by Tadmor (1973) is the adsorption of 86Kr on particulate matter and the subsequent deposition of the particles. Assuming the adsorption capacity of the particles for krypton to be identical to that of charcoal, or 2 X 1W6 g krypton/g particle (Tdmor and Cowser, 1967), and the average particulate content of g/m3 (the Environmental Protection average city air to be 0.5 X Agency secondary standard is 0.6 X lo-' g/m3 and "background" is usually estimated to be 0.3 X g/m3), an average krypton content on the particulate matter in air would be about 1.0 X 1W'O g krypton/ma air at equilibrium. However, the radioactivity of this particulate matter would be determined by the isotopic percentage of 86Kr. The degree of depletion of 85Krfrom the atmosphere by particulate adsorption would

3.3 ATMOSPKERIC DISPERSION OF 86Kr

/

19

be insignificant due to the fact that the capacity of 1.1 X 10-lo g krypton m3 air is less than lop7of the stable plus radioactive krypton in the atmosphere.

3.3 Atmospheric Dispersion of 861ir The dispersion calculstions discussed below treat two aspects of 8bKr concentrations: (a) global scale dilution leading to estimates of population-dosage for the world; and (b) estimates of the maximum concentration in the immediate vicinity of a nuclear fuel reprocessing plant. 3.3.1

Global Scale Dilution Leading to Estimates of Population-Dosage for the Wwld.

85Krdisperses more or less uniformly over the entire globe because of its half-life, 10.7 years, and the lack of significant sinks. Most previous global dispersal schemes have assumed instantaneous dilution into the entire atmosphere. However, more sophisticated analyses are available in the literature (Knox and Peterson, 1972; Karol et al., 1972). The model used here (Machta et al., 1974) considers the transport and dispersion of a 86Krsta.ck emission in 4 phases, each requiring a different meteorologica.1 treat.ment. Phase 1is concerned with long-term air concentrations near a source (within about 100 km); Phase 2 estimates concentrations in the region from a few hours to several days travel from a source; Phase 3 deals with the remainder of the first plume traverse around the world; and Phase 4 estimates global air concentrations for the remainder of the pollutant's residence in the atmosphere. Details of the model are available in Appendix A and in Machta et al., 1974. The population-weighted concentration produced by the &st two phases (first three days of plume travel) is very sensitive to the location of the source. I n part, this is because meteorological differences produce different concent.ration patterns, but a much more sigmlicant factor is the dserence in population distribution. To illustrate the effect of site location, two cases will be examined. One site, in the midwestern U.S., produces a relatively high local population dose (the first phase affects a major city, and the second phase affects the populous east coast). The second site, in the southeastern U.S. near the Atlantic Coast, is remote from any large population center. Table 10 summarizes calculations of world population-weighted concentrations for the two selected sites and compares results with those obbined from a simple instantaneous global dilution model. A uniform

/

20

3. THE FATE OF

86Kr

DISCHARGED TO THE ATMOSPHERE

TABLE10-WorM populdions weighted concentration from uniform yelease rate of 1 curie of "Kr i n 1 year

Phase Plume Travel Period

Region ABected

Cumulative Exposure

Population X Annual Average Concentration ((10-1o Person .y/mg) Midwest

Site

E. coast Site

Population X Concentrahon X Exposure Time (10-10 person .ys/ma)

EpsT (Yean)

$:%,: -

&a days 3 3-30 dam

1.2

4 4 4

3Odaystol Ye= 1-2yesrs 248 yean

U.S. and Canada Mainly N. temperate latitudes World(main1yN. Hemisphere) World World

6.2

id-

west Sitc

E ~oa'st Site

FJ;

-

1.4 2.6

0.07

7.6

7.5

3.7

1

16.3

11.5

4.4

10 a.6

10 2.6

8.4

2 68

26.3 201

21.6 197

12.8 188

2.8

0.66

2.6

a Based on 1970 populations with 2 percent per annum incroase thereafter (from United Nations 1970).

release rate of 1. Ci over one year is assumed; for an actual plant, results should be multiplied by the total annual release rate (Ci/y). The table provides values for population multiplied by annual average concentration, from a uniform release rate of 1 Ci of a6Kr in 1 year (person.y/m3), for the areas affected by each phase of plume travel. Cumulative values of world-wide population exposure (person.y2/ma) are shown for periods of 1 year, 2 years, and 68 years (lifetime) on the right side of the table. The first 3 days of plume travel (Phases 1 and 2) affect only the eastern U.S. and Canada with nearly a fourfold (5.2 to 1.4) difference in population exposure for the two sites. Concentrations during the later phases of plume travel are not significantly affected by site location. Contributions from phases 1-4 are added to obtain the cumulative exposure for the first year. The cumulative world population exposure after 65 years differs by only about 2 percent (201 to 197) for the two sites. The simple instantaneous diffusion model greatly underestimates the population exposure from the early stages of plume travel; however, since most of the world population lifetime exposure occurs when the 86Kr is uniformly distributed t.hrough the atmosphere, the difference in cumulative exposure estimates is only about 6 percent after 68 years. I t is concluded that the early stages of plume travel must be considered in detail to assess accurately the cumulative doses to populations within a few hundred kilometers of reprocessing plants, but plant location and early plume history do not significantly affect the world-wide population lifetime exposure.

3.3 ATMOSPHERIC DISPERSION OF 86Kr

3.3.2

/

21

Estimates of the Maximum Concentration in the Immediate Vicinity of a Nuclear Fuel Reprocessing Plant.

Estimates of the maximum concentration in the immediate environs of a reprocessing plant are presented for two time periods: (a) maximum credible 24-hour concentration; and (b) maximum likely annual average concentration. An estimate of the maximum credible 24-hour concentration a t the plant boundary may be obtained with the following assumptions: the boundary of the controlled area is 1 km from the stack emitting 85Kr; the stack height plus plume rise is 100 meters above ground; wind speed is 1 m/s (2 lmots); dilution conditions correspond to Pasquill Stability Type C; the plume remains within a 22.5" sector throughout the 24-hour period and no unusual terrain features affect the plume. The meteorological assumptions and resultant calculations are those recommended in AEC Safety Guides for Water Cooled Nuclear Power Plants (USAEC, 1970b). The average 24-hour concentration, in units of Ci/m3 is approximately equal to 1 X 1e6 Q, where Q is the 24-hour average release rate in Ci/s. The maximum annual average concentration (again assuming no unusual terrain features) will be estimated a t a point 1 km downwind of the stack on t.he assumption that the wind blows the effluent toward this location 10 percent of the time (the maximum annual frequency of wind in a 22.5" sector is typically on the order of 10 percent in the U.S.). Assuming a typica.1 annual distribution of dilution conditions (Type A with a 2 m/s wind speed, Type C with 5 m/s, and Type F with 2 m/s, each prevailing one-third of the time), the average annual concentration (Ci/ma) averaged over the year is calculated to be 1.1 X lop7Q, where Q is in units of Ci/s. The average a n ~ u a lconcentration, for the same source strength, is about one-hundredth of the maximum 24-hour concentration.Usingmoredetailed meteorologicaldata, the maximum annual concentration from the Barnwell plant in South Carolina was calculated (Allied Chemical, 1968) to be 70 percent of the value computed here. Similar results a t other sites tend to confirm the validity of this simple approach.

c,

Six sources of radiation associated with 86Kr are considered below: (a) photons and beta rays emitted in air due to the radioactive decay of 85Kr present in the atmosphere; (b) bremsstrahlung emitted in air including both internal, emitted when the decay occurs, and external, emitted as the electrons move through the air; (c) bremsstrahlung produced by the beta rays as they move through the skin and subcutaneous tissues; (d) photons and beta rays emitted generally in the body due to 85Kr absorbed in the tissues of the body; (e) internal bremsstrahlung emitted by the beta rays as they pass through the tissues of the body; and (f) photons and beta rays emitted by 85Krpresent in the air passages of the lungs. The dosimetry appropriate to each of these sources is discussed briefly below, and the dose rates to skin, subcutaneous tissue (adipose tissue), lungs, active bone marrow, bone, and gonads and a general dose to soft tissue of the body are estimated for a person immersed in a semi-infinite cloud of radioactive emitter with a uniform source strength of 1 pCi/m3. The results are summarized in Section 4.6. The effect of exposure to a plume of 86Kris discussed briefly. For purposes of this report, anthropometric data are based on a standard man.

4.1 Dose from Photons Produced in a Semi-Idnite Cloud

The primary photons from s5Krdecays occurring in air will be scattered by the air, and thus a continuum of photons of lower energies will be produced. The energy spectrum of these scattered photons has been calculated by Dillman (1970) for the case of a monoenergetic gamma emitter uniformly distributed in an infinite unbounded cloud of air. Since the cloud is assumed i n k i t e and the primary photons are distributed isotropically, all subsequent generations of photons will be distributed isotropically also. Thus, this energy spectrum of scattered photons in space will have no angular dependence. The calculation was This section is based on work by Committee Consultant W. S. Snyder and his associates and subsequently ~ublishedin the Proceedings of the Noble Gas Symposium, Las Vegas, 1973 (Snyder el al., 1975). 22

/

4.1 DOSE FROM PHOTONS

23

to7

5

5

2

2

to6

5

5

--

'f

2

'

j -k

"

lo2

to5

5

Y

2

lo4

IO' 2

5

5

2

2

to3

0

i

{o0 20 40 60 80 400 PERCENT OF INITIAL PHOTON ENERGY (0.5 MeV)

Fig. 3. Energy spectrum for scattered photons. (Initial photon energy = 0.6 MeV, source intensity = 1 &i/g of air). Dillman (1970).

performed for twelve monoenergetic photon sources, and the energy spectrum for secondary photons and electrons, for a source intensity of 1 pCi per gram of air when the primary energy is 0.5 MeV, is shown in Fig. 3; this would be the spectrum resulting from each volume element of the infinite cloud. These data are applicable to the radiation from W r . The dose within a phantom irradiated from a source impinging on the

24

/

4.

DOSIMETRY

surface with the angular and spectral distributions given by the infinite cloud calculation has been estimated for each of the twelve monoenergetic original sources. These source energies extend from 0.01 to 4 MeV, spaced t o make interpolation possible. The methods used and the phantom are described in MIRD Pamphlet No. 5 (Snyder et al., 1969) although some changes have been made to provide a more realistic estimate of dose for the problem posed by atmospheric 8%r. These include a separation of the legs of the phantom, a region containing testes, and a rounded region for the cranium or top of the head. The use of an ellipsoidal shape for the head is due to the fact that the sliull contains about 13 percent of the red bone marrow of the adult, and thus the additional soft tissue present in the phantom, as described in MIRD Pamphlet No. 5, might somewhat shield this portion of the active marrow. Details of the phantom are given in Appendix B. Actually, one is concerned with a person on the surface of the ground, and thus a ground effect must be considered. For an energetic photon, i.e., one having a mean-free path in air which is many times the disrneter of the body, the presence of the man on the earth's surface means that essentially half the source in air to which he is exposed (half the infinite cloud) is missing. This assumes there are no surface deposits of s6Kr, and these would be expected to be negligible in view of the arguments made in Section 3.2 concerning the fate of 86Krdischarged to the atmosphere. There is some backscattering of photons from the earth, but direct measurement of 'j°Co sources in air indicates this ground effect is probably less than 20 percent (Haywood et al., 1964; Berger, 1957). Of course, the measurements are for essentially a point source, but summation of such sources indicates an increase of dose of this order due to scattering from the ground. Thus, one may use half the intensity of the energy spectrum for photons without any great error in estimating the dose received. The argument depends on the fact that even a t energies of 10 lceV, the mean-free path of photons in air is comparable to the body height, and hence, essentially half the source is missing for irradiation of the lower portions of the body, and about 25 percent is excluded by the ground for irradiation of the upper portions of the body. For higher energies, the ground interface essentially excludes half the source. The dose rate to the various body organs from photons emitted by s6Kr in air is included in the summary set out in Section 4.6 (line 1 of Table 12). A concentration of 1 &i/rn3 (STP) is assumed, and the dose is shown per year of the person's presence in this "infinite" cloud. The dose to skin from photons is an average over a thickness of 0.2 cm extending over the entire body.

4.3 DOSE FROM

4.2

S6.Kr

IN THE BODY

/

25

Dose from Bremsstrahlung Produced in Air or Skin

Brernsstrahlung is emitted whenever a beta ray is produced or whenever the electron passes through a medium. The so-called internal and the external brembremsstrahlung is emitted from the atom of B6Kr, sstrahlung is emitted as the beta ray passes through air or tissue. The energy spectra and intensities of the bremsstrahlung produced in air and skin (as weU as tissue, skeleton and fat), have been given by Snyder et al. (1975). The resultant doses are included in the summary set out in Section 4.6 (lines 3 and 4 of Table 12).

4.3 Dose from 86Krin the Body A person immersed in an atmosphere of 86& at, say, 1 ctCi/mawould rather quickly come into equilibrium with it. The concentration in the body tissues would be the concentration in air multiplied by Ostwald's coefficient. which is a volumetric partition coefficient. Thus, (tissue concentration in pCi/g) = 10-% L X (concentration in air in pCi/ma) where L is Ostwald's coefficient. A weight related coefficient, L,, is commonly used ia tissue studies where Lu = LL/ where p is the density of the absorber. Then: X (air concentration in (tissue concentration in &i/g) = pCi/m8). Some authors (Kirk, 1972; Yeh and Peterson, 1965) have used ra formula

where frat is the fractional content of fat in the tissue. This procedure is followed here. ?'he total body can be considered as composed of two tissues-fatty tissue and nonfatty tissue, although a more detailed model considers the percentage of fat, protein and water in each tissue and the non-neutral fat fraction (Kirk, 1975). On the basis of a few measurements and in vilro studies (Lawrence et al., 1946), the Ostwdd coefficient for these two types of tissue is about Lrat = 0.45 and

LnOnr.t

= 0.07

Using weight related coefficients the equation above becomes L w timue = Lfatl~fat x fret

+

L n o n f a J ~ n o n ~ aX t

(1 - ffat).

TABLE11-Percentage oj separable adipose tissue and nonfat tissues and the Ostwald coeficieni for subdivisions o j the human bodya Separable

Adipose Tissue

Total Mssa (kg) Fat Content (kg) Oatwald Coefficient (weight related) pCi/g tissue/fiCi/g air Tissue Content bCi) for 1 &i/g in air

12.5 10 0.41

3 . 2 X lo2 3.87 X 10"

Other

Skeleton

(Bone Plus Marrow)

Soft h e s

47.5 1.5 0.083

10 2

0.131 1.0 X 10' 9.28 X 10'

64

2.36 X 104

Modified from Snyder el a l . (1975).

The tissues considered are shown in Table 11 together with the fat content and the estimated Ostwvald coefficient. On this basis, an average coefficientfor the body is obtained. However, the concentration will not be uniform, the concentrations in adipose tissue being almost an order of magnitude higher than in most tissues. Rremsstrahlung will be produced in the body by the beta rays emitted from 85Krpresent in body tissues. Because of the greater concentration of 8sKr in fatty tissues, there will be a greater source of bremstrahlung in these tissues, and the production of bl.emsstrahlung is taken here as proportional to the concentration (i.e., the fact that some portion of the range of the beta rays is outside the organ or tissue of origin is ignored). Likewise, bremsstrahlung will be produced in the skeleton to a greater extent than in soft tissues because of the higher charge number of many of the constituents of bone. The body is considered as composed of fat and nonfat tissue with the values cited above for the Ostwald coefficient. According to Tipton (1975), the reference body contains about 15 kg of adipose tissue of which 12.5 kg is separable, i.e., occurring in easily distinguishable masses of adipose tissue such as the subcutaneous fatty layer, fat about the kidneys, etc. Of this mass, some 10 kg is fat. Using the formula cited earlier, one finds:

using pad = 0.92 g/cm3 and pu ,,,.= 1.0 g/cm8. This adipose tissue is distributed rather generally throughout the body and hence is assumed here to be contained in the total body minus the totality of spec5ed organs as defined in the phantom used in MIRD Pamphlet No. 5 (Snyder d al., 1969).

4.3 DOSE FROM g6Kr lN THE BODY

/

27

The skeleton, which here consists of bone plus marrow plus connective tissues, contains a total of 1900 g of fat, most of which is distributed among 1500 g of yellow marrow. Thus using p,k,l = 1.5 g/cmS,

Only a few measurements on bone have been reported, and these have been, for the most part, on the whole bone plus marrow. Since the value of L for fat is approximately an order of magnitude in excess of its value for other tissues, it is likely that the measurements reflect largely the uptake of 8 6 K r into the marrow. The soft tissues are not devoid of fat. In addition to interstitial fat, there is a lipid constituent of most tissues which includes the essential fat. I n the remainder of the body, that is, total body minus separable adipose tissues minus skeleton, there are about 1.5 kg of essential fat out of a total mass of 47.5 kg. Accordingly, the Ostwald (weight related) coefficient is given by

Thus, assuming a concentration in air of 1 pCi/m3 = 10-B pCi/ml, one should have, at equilibrium, concentrations of 0.41 X pCi/g of separable adipose tissue, 0.131 X 10-6 pCi/g of skeleton, and 0.083 X 1W6 pCi/g of soft tissue. As mentioned above, the concentration of adipose tissue is for the "other tissuesJ' of the body that remain after all designated organs are subtracted. This is equivalent to putting 0.083 X lFs X 70,000 = 5.8 X 10-SMCiin the total body, distributed throughout all tissues. 0.131 - 0.083 X 104 X 104 = 4.8 X IF4 pCi in the skeleton (in addition to the activity already there as part of the total body activity). (0.41 - 0.083) X 1F6 X 12,500 = 4.1 X 10-8 MCi in the "other tissues" (fat) compartment (in addition to those already there as part of the total body activity). When this is done, the photon, beta, and bremsstrahlung doses due to 86Krabsorbed in these tissues and present there at this equilibrium level are found to be the values given in the summary set out in Section 4.6 (lines 5, 6, and 7, respectively, of Table 12). Actually, the calculation of the dose from the bremsstrahlung is slightly more complicated in that it is not merely the total source strength that must be subtracted as above, but also the spectrum of the soft tissue dose with the proper weighting factor; that is, (0.131 X spectrum of skeleton - 0.083 X

spectrum of soft tissues) X X lo4 must be used t.o allow for the difference in spectra of these two media. A similar remark applies for separabIe adipose tissue.

4.4

Dose From Beta Rays in an Infinite Cloud

A calculation of the depth dose in skin and subcutaneous tissue from beta rays in the infinite cloud has been made by Berger (1974). A graph of the depth dose is shown in Fig. 4. The skin will be considered here as consisting of an epidermal layer (of which the first 10 percent, the stratum corneum, consists of dead tissue, on the average) and a deeper layer-the dermis. Values for the thiclmess of layers have been given by several authors for a variety of

DEPTH IN TISSUE (cm) Fig. 4. Depth dose in tissue from beta radiation (infinite cloud of uCi/ma) (Snyder el al., 1975).

86Kr,

1

TABLE 12-Equilibrium absorbed dose rate to body organs per unit air concentration (rads rna/j&i y)* from immersion in a semi-infinite cloud of =KT

I

organ

Source Skinb

=KT in air 1 Photons in air 2 Betas in air 3 Bremsstrahlung in air 4 Bremsstrahlung in skin in the body 5 Photons in the bodyo 6 Betas in the bodyo 7 Bremsstrahlung in the bodyo 8 Betas in airways of lung

Total

Adipose Tissue

Lungs

1 . b X 10-2 1 . 2 X 10-2 1.1 X 10-2 1.8 3.2 X loMa 2.1 X 10-8 1.9 X 10-8 6.9 X 1W6 4.0 X 10-8 5.8 X

Red Bone

Marrow

Skeleton

Ovaries

4.7 X l V a 1.3 1.4 X 1 V 2 1 . 5 X 3.6 X l W S 4.0 X lop8 1.1 X l(r8 2.5 3.7 X l C B 1.1 X 10-6 2.1 X lVB 9.9

Testes

Total Body

1 . 2 X 1W2 X X l V a 2.3 X loea 9.1 X 1 V 6 X

2.8 X lVB 3 . 1 X l V B 2.3 X l W B 2.2 X lVG 2.3 X 10-6 2.2 X 1&6 2.4X 10-6 2.3 X 7.7 X 10-4 3.7 X 1 V 4 3.7 X 1 V 4 3.7 X 1 V 4 7 . 3 X 1 V 4 3.7 X 3.7 x 10-4 1.1 X 4.0 X 10-7 7.7 X 10-7 6.9 X 10-7 1.1 X 1 V 6 9.1 X 10-7 7.7 X 10-7 9.1 X l V 7 7.7 X -

1.8

-

1.8 X 1W2

-

-

1 . 5 X 1 V 2 3 . 1 ~ 1 0 - 1~ . 8 X 1 V 8 1 . 9 X 1 0 - 2

-

-

6.2X1W8 l.6X10-z

-

1.5X10-2

For comparative purposes, since the Quality Factor (Q) equals one here, the absorbed dose in rads equals the dose equivalent in rems. b Thelensesof the eyes would be a t a depth of 3-4 mm and hence would receive essentially no irradiation from the betas emitted in air. The dose rate would be expected to be much the same as the average dose rate to the skin due to photons in air (i.e. 1.8 X 10-2 from lines 1 and 3 ) . a These values may be subject to adjustment.

30 /

x 1

b

31

?

.-

bbb

e 3 e . m

Lbb rlrld

NhlN

1'9'9

n

.- -

991 u

"

hlhlrl u

m

-?Z?K$

xxxxx 1 1 1

bbbbb

m

~ X X X ~ X X X

br13d

4. DOSIMETRY

gs

5"

35

.%.a

4

. I

; :1 : 2

4.6 SUMMARY OF DOSES

/

31

regions of the body (Southwood, 1955; Whitton, 1973). For example, a recent series of measurements of Whitton (1973) indicates values of 30 to 80 pm for the epidermis on various regions of the body, exclusive of hands and feet, with a mean thickness of perhaps 50 pm. This would indicate a somewhat smaller value for the stratum corneum of 5 pm. Thus, for an air concentration of 1 pCi/m3, an average dose rate to a h (50 pm) due to beta rays in air is about 1.8 rads/y as shown on line 2 of Table 12, with a maximum dose rate of 2.0 rads/y.

4.5

Dose from 86Krin the Airways of the Lungs

A certain amount of s6Kr will be present in the air passages of the Lungs. The volume of these air passages varies considerably as the person breathes, but an average value would be about (3.5 0.5) l i t e ~ = 4 liters, where the average functional residual capacity is 3.5 liters and the average tidal volume is about 0.5 liters for a standard man in the resting state (Morrow et al., 1966). The activity present in the lung air is 0.004 pCi, assuming that the air in these passages is a t the same concentration as the outside air. At equilibrium, the person would receive a lung dose rate of 1.8 X 1W2rads/y, as shown on line S of Table 12, this being essentially the dose rate from the beta radiation. The dose rate to lungs from the gamma radiation would be approxirna,tely 3 orders of magnitude less than this due to the low gamma yield and small absorbed fraction. The dose rate to ovaries and testes from thk source in lung is 8.8 X 10-8 rads/y and 1.5 X 1W8rads/y, respectivelv. The red bone marrow dose rate would be about 5.8 X lo-' rads/y.

+

4.6 Summary of Doses Table 12 summarizes the total equilibrium absorbed dose rates to various body organs, per unit air concentration, for immersion in a semi-infinite cloud of S6Kr. These quantities have also been calculated by others, using various approaches to the problem. The method to be used in any instance, in the absence of experimental data, is primarily a matter of choice. Table 13, adapted from Soldat et al. (1975), lists the results obtained by several workers. The assumptions used by the various authors were not always the same, this being especially true of the lung volume and the depth at which the 'skin' dose was calculated. When the variations in assumptions are taken into account, there is reasonable agreement among the values obtained by the different authors.

5. Projected "Kr Concentrations and Dose Commitments I n this section, the projected concentrations of 85Kr will be estimated for various times in the future, and these estimates d l then be converted into projections of annual population dose equivalent rates (personrem/y) to the various organs. The projections have been made only to the year 2000, because, as noted earlier, uncerta.inties of the estimates increase with time and we are of the opinion that no useful purpose would be served by projecting the concentrations and dose commitments beyond the end of the century. Such estimates will be more meaningful in five or ten years when additional data are available which, if necessary, can be used to modify the physical and biological models used in this report.

5.1 ssKr Concentrations

The historical concentrations of 85Kr in the atmosphere (UNSCEAR., 1972) can be projected into the future, assuming no control of SSKr emissions, from the material presented in Sections 2 and 3 on nuclear power projections and environmental dispersion. The past and projected concentrations are shown in Figures 5 and 6. Concentrations in 1970 are estimated to have been approximately 15 pCi/m3 (Shuping et al., 1970), with future concentrations projected to increase by a factor of about 100 by the year 2000. The variation in concentration with latitude shown in Fig. 6 is probably somewhat understated, as all 85Kr generation is assumed to occur in the northern hemisphere, between 35' and 45" N. The projected concentrations of 85Kr first given by Coleman and Liberace (1966) for dilution in the entire atmosphere are shown for purposes of comparison (Fig. 6). The present projections for the year 2000 are higher by from 25 to about 50 percent, depending on latitude. Much of the difference is accounted for by increases in the projected nuclear generating capacity. 32

5.1

86Kr

CONCENTRATIONS

/

33

YEAR

Fig. 5. Concentration of 86Kr measured in northern hemisphere air samples. (Assembled from various sources by UNSCEAR, 1972, p. 72.)

The difference in the present estimate for the year 2000, due to latitude, is only 20 percent, reflecting the long life of 86Krrelative to the equilibration time for hemispheric mixing. Estimates can be made of the uncertainties that, enter into the projections shown in Fig.6. Assumptions regarding reactor mix are important because of the fairly large variation in 86Kr generation per fission event, depending on the type of fission (see Section 1.2.3). Using the two sets of projections by Coleman and Liberace (1966) and by Nichols and Binford (1971) as a guide, a rough estimation of the maximum variation due to reactor mix yields a factor of a.bout 2 by the year 2000. Estimates for earlier years should be more reliable. Similarly, the uncertainties due to projections of installed nuclear power should be fairly small through t.he mid-19802s,but may grow to a factor of about 3 (estimated from Table 4) in the year 2000. Uncertainties due to meteorological calculations should not exceed a factor of 2 in terms of global concentrations.

34

/

5.

8LKr

CONCENTRATIONS AND DOSE C O M M I ~ N T S .

..

+Coleman & Liberace

1. Nichols and Binford (1971) nuclear power projections 2. Continuous releases of 86Kr throughout each year

1960

1970

1980 YEAR

1990

2000

Fig. 6. Predicted average concentrations and annual skin dose equivalent rates due to 86Kr in the atmosphere (1955-2000).

The uncertainty in the currently projected concentrations will be reduced markedly as the expected mix of reactor types and the projected generating capacit.y become more reliable. I n this report, the source strengths are those of Nichols and Rinford (1971), which tend to be higher than estimates derived from other sources. The dose estimates thus derived probably err on the high side.

5.2 PROJECTED POPULATION DOSE COMMITMENTS

5.2

/

35

Projected Population Dose Commitments

The method of computing the dose to the various organs, the projected.concentrations of sSKr, and the distribution of the world's population, enable one to compute the population dose commitments for each year of operation of the nuclear power industiy. This type of analysis proceeds naturally from the data present in Table 10 for cumulative exposures from a release of 1 curie of "Kr. Those data, for cumulative exposures of 1, 2, or 68 years, yield world population dose commitments over those time spans if corrected to the appropriate base year population estimate, and then multiplied by the dose rate for a particular organ times the number of curies released in the base year as given in Table 8. This has been done and the results for skin, skeleton, and red bone marrow are given in Table 14. The most significant population dose commitment, that to the skin, grows from 2.4 X lo6personrem (for a 68-year period) for the year 1970 release to a 6.6 X lo7 person-rem commitment for the year 2000.

TABLE 14--Estimated world populalion dose commitments from annual worldwide 8 6 Kreleases. ~ Year

Assumed Annual World sbKr Po ulataon Produc(''lions) lion

A n n u l Population ~ o s Commibnenb e (103 person-rems) -

Skin 1 Year

68 Yeam

Refw t o Fig. 6 for estimates of the mean skin dona

Skeleton 1 Year

68 Yean

Red Bone Marrow l Year

68 ~

e

i

6. The Biological Significance of the Absorbed Dose The biological effects to be expected from long-term exposure of the population to low-level environmental radiation have been critically reappraised in recent reports by the National Academy of Sciences--National Research Council Committee on the Biological Effects of Ionizing Radiations (NAS-NRC, 1972), and by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 1972). As has been concluded in similar reviews during the past two decades, both Committees reported that the principal potential risks from exposure to ionizing radiation are genetic effects and carcinogenic effects. The risks cannot be assumed to disappear entirely at low doses; i.e., to follow a threshold type of dose-response relation. Although each report emphasized the uncertainty pertaining to dose-response relationships a t the low doses and low dose rates of interest, and the corresponding reservations that must be attached to any estimates of the risks of low-level irradiation, numerical estimates of genetic and carcinogenic effects were presented only in the NAB-NRC report. The NAS-NRC estimates of carcinogenic risk were at radiation levels far below the observed data levels. These estimates were made in response to the charge given the Committee to provide numerical estimates at such exposure levels. The Report extrapolated by a factor greater than 1,000 with respect to dose and by factors from 100 million to a billion with respect to dose rate. The body of the NAS-NRC Report stresses the possible factors that might invalidate strict use of linear extrapolation, but the Committee justified its use on pragmatic grounds as a means of estimating risks a t low doses and dose rates. The same extrapolation models may, with the reservations inherent in such extrapolation, be applied to estimates of the maximum biological effects associated with estimated doses from 86Kr.

6.1 Genetic Etrects As an example, to illustrate the maximum possible genetic effects of exposure to radiation a t low doses and dose rates, an upper limit can be

6.2 OVERALL CARCINOGENIC EFFECTS

/

37

inferred from the NAS-NRC Report which estimates that exposure of the population to a gonadal dose equivalent of 5 rem per generation (roughly equivalent to 170 mrem per year for 30 years) could cause up to 60-1000 cases of genetic detriment per lo6offspring in the FI generation and 30Cb7500 cases per lo6offspring in later generations after atta.inment of genetic equilibrium. The NAS-NRC Report assumed that these cases will occur against a natural incidence of 60,000 cases per lo6 offspring (see their table No. 4, p. 57). We find that the world mean annual gonadal dose from 85Kr is estimated to have been 2 X loL4mrad in 1970 and will increase to about 2 X mrad in 2000 A.D., a factor of 100. If the maximum frequency of genetic disabilities were to vary as a linear function of dose, then the corresponding maximum frequencies for the estimated doses attributable to *bKr in the year 2000, derived by direct extrapolation from the above values, would be about 100 times the values in 1970. If, for a mean annual mrad from 8bKr,there might be a maximum of gonadal dose of 2 X 0.07-1.2 cases of genetic disability per lo9offspring, this should be compared with 60-1000 cases per lo6 offspring from 170 mrem, a factor of about lo6. While the 53-1320 genetic disabilities predicted for the year 2000 seem small, these would continue to grow in magnitude if no controls urere imposed on 85Kr releases. We do not endorse this kind of calculation, but it does serve to illustrate, even in the extreme, the relatively small contribution of effects from 85Kras compared witjh other possible sources of deleterious effects.

6.2 Overall Carcinogenic Effects Based on the excess mortality from cancer in atomic bomb survivors, patients treated with radiation for various non-neoplastic diseases, and certain other irradiated human populations, the NAS-NRC Report (1972) estimated that the maximum risk of malignant growths due to continuous whole body irradiation might be as high as 150-200 cases per million people per rad per year. If this held a t the levels of exposure due to natural radioactivity, it could account for as much as 1 percent of the cancer death rate. If the frequency of cancer deaths is assumed to vary as a linear function of the mean dose to the whole body, irrespective of the dose rate, then the corresponding frequencies of cancer death in the U.S. for doses attributable to 86Kr in 1970 and 2000, derived by direct extrapolation from the above values, would be 0.007 and 1.1 respectively against a baclcground of about 600,000 cases per year. These estimates assume no change in the present cancer death rate of 1600 cases per million, and a

38

/

6. BIOLOGICAL SIGNIFICANCE OF THE ABSORBED DOSE

U.S. popula,tion of 300 million in the year 2000. Again, even using these risk coefficients, which we believe lead to overestimation of the risk, the contribution from 85Xris seen to be very small compared to that from other radiation sources.

6.3 Carcinogenic Effects on Skin Because of the relatively higher dose that 86Kr can be expected to deliver to the skin, as compared with other tissues of the body, the risk of carcinogenic effects of 86Kron the skin deserves special consideration. Numerical estimation of the risk of induction of skin cancer is complicat,ed, however, by the deart,h of dose-response data for this effect in human beings. The absence of an observed excess of skin tumors in A-bomb survivors and certain other irradiated human populations, in which an excess of other types of neoplasms has been well documented, argues that the skin is appreciably less susceptible to radiation carcinogenesis than are several other tissues of the body (e.g., bone marrow, bronchi, breast, thyroid, bone). Even in view of the comparatively higher doses the skin may be expected to receive in comparison with deeper tissues of the body (Table 12), it is questionable whether the skin is sufficiently susceptible so that the risk of cutaneous carcinogenesis would contribute significantly to the total cancer risk. It should also be noted that while this is a very serious disease, it is one of the most easily controlled of all the malignancies.

6.4

Possible Interaction of Ionizing and Ultraviolet Radiation

The possible interaction of the radiation from 85Kr and solar ultraviolet radiation should be mentioned. The issue of co-carcinogen interactions is probably significant in the quantitative msessment of cancer risks from most environmental carcinogens. It may be entirely fallacious, for example, to assume that the hazard from a given atmospheric level of 85Kris the same for dark-skinned persons, who have a very low natural incidence of skin cancer, as for such fair-skinned persons as live in certain regions in Australia where 25 percent of white males develop one or more basal cell carcinomas by 65 years of age (Silverstone and Gordon, 1966). That the interaction of ultraviolet and ionizing radiation is important for the induction of skin cancer is suggested by an ongoing follow-up study of children who received x irradiation of the scalp as an epilation

6.4 IONIZING AND ULTRAVIOLET RADIATION

/

39

procedure in the treatment of tinea capitis. The incidence of basal cell carcinoma of the scalp in the irradiated population 25 years after treatment is 1.5 percent. However, all of the cancers have developed in the irradiated white population while both the irradiated negroes and whites show an equal amount of radiation-induced hair damage (Shore and Albert, in press 1975). I t is impossible to predict the impact of low-level 86Krexposures on the induction of skin cancer by ultraviolet radiation in the absence of direct evidence. Both agents are mutagenic and carcinogenic. However, their modes of action are different in that W causes thymine dimer formation in DNA whereas ionizing radiation causes DNA strand breakage. At one extreme, the carcinogenic effects of the two agents may be independent so that a negligible carcinogenic risk from would add a negligible excess risk to the already substantial burden of UV-induced skin cancer. At the other extreme, small exposures to sSKrbeta radiation in combination with UV would have the same d e c t as a large increase in W exposure. W exposures vary considerably according to geographic region, occupational and personal habits. The estimation of cancer risk from 86Krdepends on learning how ionizing radiation interacts in the skin with different levels of W exposures as well as chemical carcinogens, since the latter must also make some contribution to t>heexisting burden of skin cancer. In order to understand better the implications of long-term 8SKrreleases to the atmosphere, epidemiological and laboratory studies should be undertalcen to define the nature and degree of interaction, if any, of W radiation with ionizing radiation in the induction of skin cancer.

7. Status of "Kr Removal from Waste Gases The extent to which S6Krfrom reactor operations or reprocessing of irradiated fuels can be controlled will depend on the availability of equipment to remove 86Krfrom the various effluents. Slansky et al. (1969) examined the characteristics and costs of the several processes available for krypton holdup and recovery. IIis results are summarized in Table 15. All processes except those involving entrapment by clathrates have been found to remove more than 90 percent of 86Kralthough, as he points out, pilot plant scale experience was limited and was nonexistent with several processes. Also, the capital and operational costs listed for a threc metric ton per day plant can only be considered approximations, since sufficient information was not available to make detailed cost comparisons. Slansky (1971) subsequently updated his review of the separation processes for noble gas fission products, adding considerable details on each process. His tabular comparison of processes remains essentially unchanged (with only the addition of electrostatic diffusion) and he again emphasized that detailed cost comparisons require more data (Slansky, 1971). These cost estimates may escalate depending upon the need for such things as redundant process lines, extensive pre-purification of the gas, and additional containment structures. I n a more recent survey, Nichols and Binford (1971) also summarized the development status of processes that are potentially applicable for holdup or decay of krypton and xenon. The results of their survey are in agreement with thosc of Slansky and their summary which follows, provides a brief elaboration of all but one of the processes included in Table 15.

7.1 Adsorption at Ambient Temperature

The adsorption of noble gases on charcoal or molecular sieves a t ambient temperatures is the process that has been studied most extensively 40

7.2 CRYOGENIC ADSORPTION

/

41

(Slansky, 1971;Nucleonics Week, 1971a). This method is effective for interim holdup of xenon and krypton because selective adsorption and desorption causes these gases to move much more slowly through a packed bed than the air or other carrier gas. The process is not suitable for recovery of krypton and xenon since it does not provide for withdrawal of a concentrated product. In short, this method is suitable for delaying the release of waste gases for a period s&cient to allow for decay of the shorter-lived nuclides of the noble gases. It is not effective for control of sSKr. The primary disadvantage of room temperature adsorption is that very large bed volumw are required to provide appreciable holdup. Also, a fire hazard exits from the use of charcoal, which has low thermal conductivity, in an environment that includes oxygen and heat production by radioactive decay. The use of molecular sieves, typically inorganic zeolite-type (metal alumino-silicate)materials, avoids the fire problems, but the materials are expensive and require the use of beds that are two to four times larger than charcoal beds of comparable holdup ability. The ambient-temperature adsorption process has been used in a number of U.S. research reactors and has been in use since 1966 in the KRB reactor in Germany. Another power reactor in Germany has used this system since 1968, and a third German reactor using this system is due to come on line. The German company that markets the system can fumish a charcoal system that will reduce t,he radioactivity of BWR effluent by a factor of 2000 by providing three days of holdup for krypton and 70 days for xenon (Nucleonics Week, 1971a). Such a system for an 1100-MW electric power BWR requires five cha.rcoaJ tanks, each 1.8to 2.7 meters in diameter and 15 meters long. Somewhat smaller and less bulky charcoa.1 absorption systems that provide radioactivity reduction factors up to 200 are available.

7.2

Cryogenic Adsorption

Adsorption on charcoal at liquid nitrogen temperatures permits the use of a smaller adsorption bed and is adaptable for recovery of krypton and xenon by a process of temperature cycling (Wirsing et al., 1970; Offutt and Bendixsen, 1969). This process for recovery of -ton and xenon was demonstrated on a large scale at the Idaho Chemical Processing Plant (ICPP) about 15 years ago. Because the beds are cooled and heated alternatively, the refrigeration costs are very high. Other disadvantages are the fire hazard and the possibility of explosion of hydro-

42 /

7. STATUS OF

REMOVAL FROM WASTE GASES

Permselective membranes Clathratt! precipitation

99 per cent

Bench scale work only; no engineering UnLaboratory studies known only; engineering tests needed

mKr is collected aa a storable solid

Membranes sensitive t chemical High power costs Needs concentrated feed gas Crystallization step slow

1500

'

200

Not trvnilable Not available

A11 of the processes for the removal of 86Kr from off-gases from nuclear fuel reprocessing plants require some pretreatment of the dissolver gas except possibly the selective absorption process. The cost data presented are for a plant which processes three metric tons per day of uranium. Comparative costs for alternatives to off-gas treatment for the control of radioactive stack emissions are available. For instance, disposal of the gases to ground reservoirs would require a capital cost of $345,000 for a plant of the same size, and operating costs would range between $75-100 per metric ton of uranium. Facilities for the storage of tho off-gas during meteorological conditions unfavorable for safe atmospheric dispersal would cost $1 million and operating costs could run t o $100 per metric ton of uranium, depending on the length of storage time. The most drastic alternative, shutdown of the plant during unfavorable conditions, would involve a loss of $15,000-$30,000 per metric ton of uranium capacity for the duration of the S ~ I U ~ ~ O W ~ .

Adapted from Slansky et at., 1969. [Reprinted with permission from Environmental Science and Technology 3. 446 (1969). Copyright held by the American Chemical Society.]

2 $'

d0 M

44

/

7. STATUS O F

REMOVAL FROM WASTE GASES

carbons, nitrogen oxides, and ozone (produced by irradiation of oxygen). The system also requires prior removal of gases that would freeze a t liquid nitrogen temperatures and plug the adsorbers. The disadvantages of the cryogenic system are such that it cannot now be recommended for recovery of krypton and xenon, but the process does have potential application for interim holdup of effluent gases.

7.3 Cryogenic Distillation

Cryogenic distillation provides an effective, continuous, small-size system for separation of gases based upon their relative volatility (Offutt and Bendixsen, 1969; Nucleonics Week, 1971b; Holmes, 1971). This type of process is used commercially for isolation of the components of air a.nd is being used intermittently to remove radioactive xenon and krypton from an off-gas stream at ICPP. The process is capable of recovering krypton and xenon in a relatively pure form suitable for direct bottling in gas cylinders. A serious concern in this process, particularly when applied to a fuel reprocessing plant, is the explosion hazard that results from the presence of ozone or mixtures of liquid oxygen with hydrocarbons and nitrogen oxides. The L i d e Division of the Union Carbide Corporation has a contract to supply cryogenic distillation systems for 99.9 percent recovery of noble gases from the effluent of three BWR units at the proposed Limerick station. I n addition, they have designed a cryogenic distillation system for use in the proposed Newbold Island plant (Nucleonics Week, 1971b). Cryogenic distillation is considered to be one of the more promising processes for krypton and xenon recovery.

7.4 Selective Absorption The study of the separation of noble gases from air streams by adsorption in (or extraction by) chlorofluoromethanes has progressed to the nonradioactive pilot plant stage at the Oak Ridge Gaseous Diusion Plant (Merriman et al., 1970; Stephenson et al., 1970). The system is versatile, continuous, and adaptable to scaleup. It also appears to be considerably less subject to fire and explosion than the previous processes. Primary questions that remain to be resolved in further development work relate to the tolerance of the system to con tarn in ant,^ in the off-gas streams, the effects of radiation damage on the solvent, and corrosion

7.6 CLATHRATE

PRECIPITATION

/

45

problems that may result from the evolution of fluorine and chlorine. Selective absorption is a promising method for recovery of krypton and xenon from both reactors and reprocessing plants.

7.5 Permselective Membranes The permselective membrane process for recovery of krypton and xenon from air has been investigated on the laboratory scale a t Oak Ridge National Laboratory (Rainey et al., 1971). This process, which is based upon selective permeation of gases through silicone rubber membranes, operates at ambient temperatures but requires differential pressures across the 0.7 mil (0.18mm)-thick membranes of as much as 50 psi (0.34 MPa). The process requires many stages for effective separation. A workable large-scale process would require the development of a method for packaging the membranes to densities of several hundreds of square feet (-30m2) of active membrane area per cubic foot ( 4 . 0 2 8 ma) 3f volume. The economic viability of the process would require a very large production of membranes to reduce substantially its price below the present value of $10 per square foot (930 cm2). Some questions wilh respect to the radiation stability of the membranes for some reactor applications also remain. The Oak Ridge National Laboratory development tvorli on this process has been curtailed in favor of the fluorocarbon absorption process.

7.6 Clathrate Precipitation The precipitation of noble gases from organic solvents as solid clathrates has been investigated on a laboratory scale (Keilholtz, 1966-1967; Clark and Blanco, 1970). The process requires prior absorption of the krypton and xenon in an organic liquid at a pressure of about 1000 psi (6.89 MPa). The clathrates form very slowly, even a t these high pressures, and are known to be decomposed by radiation and heat. The clathrates, as well as all of the known compounds of krypton, are unstable at temperatures higher than about 50°C (327°K). At present this process can be regarded as little more than a laboratory phenomenon. In the future it may have application to the solidification of radioactive noble gases for storage.

8. Discussion The biological significance of the 8% accumulation is the basic factor that should influence policies governing the extent t o which release of 86Krto the general atmosphere should be reduced. I t has been shown that fuel reprocessing plants will be the main source of this nuclide. Minor amounts will issue from the reactors of the world, but i t appears that this will be far less than 1 percent of the total. Thus, as an interim policy which should certainly be suitable for the next ten years, the releases from reactors can be given lower priority and attention directed at the fuel reprocessing plants. Research and development programs of practical systems for the removal of 85Krare making progress, and prudence would seem to dictate that the fuel reprocessing plants be equipped with 85Kr removal systems as soon as the technology is practicable. The significance of the projected doses to human populations, for the levels of 85Xr discussed above, cannot be evaluated with confidence because of a lack of information on the biological effects of low levels of radiation. Well-designed experiments must be conducted during the next decade to add to our present knowledge. The most pressing issue is whether the build-up of 85Krwill increase the incidence of skin cancer in the world's population. The projected skin dose will average about 2.0 mrem/y by the year 2000 and could be 10 to 100 times higher by the year 2050, assuming that all 86Kr in gaseous wastes from the nuclear industry is not contained, but is released to the atmosphere. By the year 2050, the sldn dose from 85Krcould thus begin to approach the exposure received from the external component of natural radiation, which averages about 75 mrem/y. Since skin cancers are the most common form of neoplasm, it would seem worthwhile to undertake epidemiological studies of the incidence of skin cancer in otherwise comparable populations exposed to different levels of ionizing radiation. There are wide variations, from 60 mrads/y to several hundred mrad/y (Eisenbud, 1973). Additionally, hundreds of thousands of radiation workers (Klement et al., 1972) annually receive whole-body doses several times greater than the absorbed dose from natural background. The question of whether there might be an interaction between ultraviolet radiation and ionizing radiation is one which can be answered in 46

DISCUSSION

/

47

studies on experimental animals and it is recommended that such research be initiated. I n this report the subject has been addressed from the point of view of the United Statea atomic energy program. It is estimated that by the year 2000, the United States installed nuclear electric power capacity will be about 1000 GW compared to nearly 5000 GW for the world. Any policy adopted by the United States would thus deal with about 20 percent of the B6Kr generated in the year 2000. This is clearly a general question that requires careful international collaboration and the NCRP urges that the International Atomic Energy Agency and the International Commission on ~ o l o g i c a Protection l give prompt attention to the need for developing policies that will be acceptable on an international scale.

85Kris a beta-emitting fission product with a half-life of 10.7 years. Because of the characterietic inertness of the noble gases, this radionuclide tends to accumulate in the atmosphere with the concentration at any given point being determined by the rate at which it is introduced to the atmosphere, by meteorological diffusion, and by radiological decay. Neither the oceans nor the land surfaces act as significant sinks. Naturally-occurring 85Kr due to spontaneous fission of uranium and cosmic ray-induced atmospheric reactions occurs only in insignificant traces, and has been overwhelmed in recent years by production of this nuclide in weapons testing, reactor operation, and fuel reprocessing. The principal sources of 86Kr to date have been production of plutonium for military purposes and the atmospheric testing of nuclear weapons. I t is estimated tha.t approximately 5 megacuries of 86Krwere introduced into the atmosphere from weapons testing between 1945 and 1962. Plutonium production in the United States introduced about 15 megacuries as of 1966, by which time the process was sharply curtailed. Additional 85Kr has been contributed by plutonium production in other countries. Emission of 85Krfrom the nuclear fuel cycle will increasingly become the dominant source of this nuclide. Emissions from operating reactors are and will continue to be insignificant compared to the releases from fuel reprocessing plants. I n the absence of emission control, the 86Kr content of the atmosphere can be expected to increase for the remainder of this century and beyond due to the burgeoning nuclear energy industry. An additional source of 85Kr may be the utilization of nuclear explosives for peaceful purposes. Depending on one's assumptions as to the size of the nuclear power program and the types of reactors to be utilized, it is estimated that the atmospheric inventory of 8% by the year 2000 from reactors throughout the world will be between 3600 and 6200 megacuries. The dose to humans results from their immersion in the atmosphere containing 85Kr. The critical organ is the skin, with the dose to the gonads and whole body being lower by orders of magnitude. I t is estimated that the skin dose from ddiffused in the atmosphere in 1970 was about 0.02 rnrem/y, and that it will increase more than one hundredfold to about 3 mrem/y by the year 2000. This assumes no efforts to control 48

SUMMARY

/

49

releases of the 86Kr. The whole body dose is estimated to have been 2 X mrem in 1970 and may increase to 0.02 rnrem/y in the year 2000. 86Krcan be eliminated from gaseous waste streams to the extent of 98-99% by several processes now in various stages of development. These include fluorocarbon extraction, cryogenic distillation, low ternperature adsorption on charcoal or silica beds, use of selective membranes, and precipitation as a clathrate. The most pressing question is whether the low level skin dose resulting from the build-up of 86KrwiU increase the incidence of skin cancer in the world's population. I t is not possible to answer this question unequivocally, but the sldn has proven to be a relatively radioresistant organ and it is significa.nt that an increase in skin cancer has not been observed among the Japanese atomic bomb survivors. The dose from 86Kr for the next several years will be of such a low order as to preclude the need for installation of recovery systems. Rowever, as such systems become available for full-scale application, their installation in fuel reprocessing plants should be considered in relation to the costs of such installations and the benefits, if any, that would result.

Calculation of Long-Term Air Concentrations The f i s t phase deals with the f i s t 6 hours of plume travel, or distances to about 100 km. A local wind-rose is used to assign material emitted during the year to directional sectors in proportjon to the frequency with which the wind blows into each sector. In the second phase climatology of air trajectories is used to estimate the dispersal of source material for travel times up to 5 days and distances up to a few thousand kilometers. The third phase deals with the remainder of the k s t plume paasage around the earth (about 30 days). In this phase an effective diffusion coefficient (time dependent) is used to estimate the lateral spread of the plume about an average trajectory derived from clirnatological flow patterns in the lower atmosphere. This trajectory carries the plume from the east coast of the U.S.across the Atlantic to Europe, Asia, the Pacific and back over North America. The fourth phase (beyond 30 days) involves a computer model of global diffusion in which uniformity around circles of latitude is assumed. During phase four, there is continued dilution due to north-south and upward mixing. It is estimated that after about two years, the 85Kr becomes nearly uniform throughout the atmosphere, so that subsequent concentration changes are due almost entirely to radioactive decay. Mean annual pollutant concentrations are combined with demographic data to estimate population exposure for each phase and total worldwide population lifetime exposure. To illustrate the use of the model, we will assume a hypothetical nuclear fuel reprocessing plant in lllinois with 8 uniform release rate of 1 Ci/y of 86Kr. In this example, air concentrations resulting from 1 year of operation (total release of 1 curie) are calculated. Realistic estimates for an actual plant can be obtained by multiplying by the actual emission rate (Ci/y).

In this earliest phase of plume travel, a local wind rose is used to determine the horizontal distribution of the average annual concentration 50

CALCULATION OF LONG-TERM AIR CONCENTRATIONS

/

51

a t ground level. Material emitted continuously throughout the year is assigned to each sector in proportion to the frequency of time during which the wind direction lies in the sector. The vertical distribution of material is given by a half-Gausian distribution whose mean is at ground level; the standard deviation (a,) of the Gaussian curve can be related to the vertical diffusion coefficient as shown below. The standard formula (Turner, 1970) for the mean concentration at. ground level (Ci/ma) from a continuous point source, is

el

where a. K,

=

vertical diffusion coefficient = 5m2/s emission rate = 1 Ci/y = 3.2 X 1F8Ci/s f = frequency of wind in sector fi = mean .wind speed in sector (m/s) e = sector width: 22% degrees or a/S x = distance from source (m) t = plume travel time (s) The value chosen for the vertical diffusion coefficient (K, = 5 m2/s) is considered to be a reasonable day-night, all-weather annual average for the lower troposphere (Machta, 1974). However, there is considerable variability with altitude, season, and weather conditions, and the appropriate mean value is uncertain. Values of ti and f are obtained from wind-rose statistics. The calculated air concentration pattern for the assumed source in Illinois is shown in Fig. A-1.

&

=

=

Phase I The second phase deals with plume dispersion at distances to a few thousand kilometers or several days travel time. At this range, singlestation wind data are no longer applicable and the model uses a climatology of air trajectories to estimate lateral dispersion and long-term concentrations. A computer program has been developed to construct trajectories from historical wind data tapes and calculate air concentrations along each trajectory. For the illustration provided here, trajectories mere calculated 4 times per day for one month out of each season to obtain an approximation of the average annual air concentration. Plume concentrations (Ci/ma) were calculated from

52

/

APPENDIX A

Fig. A-1. Mean annual surface air concentration contours the release of 1 Ci/y of 86Krat Morris, Illinois (Phase 1).

where u

Ci/ma) for

wind speed along the trajectory (m/s) distance perpendicular to the trajectory (m) standard deviation of the plume in the direction perpendicular to the trajectory (rn);[a, in nautical miles (1.852 km) is assumed numerically equal to plume travel time in hours] Other symbols and parameter values are the same as in Eq. (A-1). The computer calculated mean annual air concentration pattern over the United States and Canada is shown in Fig. A-2. =

y

= a, =

Phase 3 The third phase deals with the remainder of the first plume passage around the earth (about 30 days). Mean annual air concentrations are

CALCULATION OF LONG-TERM AIR CONCENTRATIONS

Fig. A-2. Mean annual surface air concentration contours Phase 2.

/

53

Ci/ma) from

calculated from the spread of the plume about a single average trajectory derived from the 12 mean monthly 850 mb wind charts. The annual average concentration a t any point was calculated from Eq. (A-2) as in phase 2 except that for phase 3 it was assumed that a, (nautical miles) = 2 (1) where t is travel time in hours. Actually, available tracer information suggests that u, = t is a good approximation for individual clouds of material (instantaneous releases) (Heffter, 1965). This rate of lateral spread has been arbitrarily doubled to account for the effects of longterm meander of a continuous plume. However, after 15 days of lateral

54

/

APPENDIXA

Fig. A-3. Mean annual surface air con~ent~ration contours (lo-" Ci/ma) from Phase 3.

spread, the growth with time of the lateral standard deviation is stopped to prevent an unrealistically wide north-south spread from 15 to 30 days. A study of the dispersion of computer-calculated trajectories will be used to obtain more satisfactory estimates of the effectivelateral spread of the long-term mean plume during this phase. The average trajectory carries the plume from the east coast of the U.S.across the Atlantic to Europe, Asia, the Pacific and back over North

CALCULATION OF LONG-TERM AIR CONCENTRATIONS

/

55

America, as shown by the dashed centerline in Fig. A-3. Concentrations in the shaded area of Fig. A-3 were calculated in earIier phases.

Phase 4 In the fourth phase (beyond 30 days) concentrations are calculated using a computer model of global diffusion (Machta, 1974). During this period, concentrations are assumed to be uniform around the latitude circles and diffusion takes place only in the north-south and vertical directions. This assumption is also made in other global diffusion models (Karol et al., 1972; MacCracken, 1973). Values of the diffusion coeficients (K, averages 3 X 106m2/s)are varied with latitude, altitude and season in accordance with experience in fitting tracer data on a global scale. Resultant mean annual surface air concentrations for the source assumed in this example (1 Ci of s% emitted uniformly over 1 year) are shown in Table A-1 for 20" latitude bands. As early as the second year TABLE A-l-Phase 4 average surface air concerrtration

Ci/ms) of a6Kr( I C i emitted uniformly over 1 year i n 6&60nN latitude bands) Latitude

Year

'09 70"N

70% 50"N

50"-

30°N

30'10"N

10°N10"s

1030%

30'-

5O0-

505

70's

7O0905

All Latitudes

Year

Average Surface Air Concentration

Year

Average Surface Air Concentration

Year

Average Surface A!r Concentrabon

First year values are acti~allymean annual concentrations from the end of the first month t o the end of one year.

56

/

APPENDIX A

the north-south gradient is very small and after that latitudinal differences are too small to record. Virtually all of the decrease in concentration after two years is due to radioactive decay rather than further dilution from vertical mixing through the model which extends upward to 40 krn. The ma11 annual concentration during the first year, a t a spec8c location is obtained by adding the value from Figs. A-1, A-2, or A 3 (first plume traverse around the globe) t,o the appropriate first year value from Table A-1. For succeeding years only Table A-1 is used.

APPENDIX B

Phantom Description The legs are described by the following inequalities (see Fig. B-l), using the coordinake axes defined in MIRD Pamphlet No. 5 (Snyder et al., 1969):

where the plus or minus sign in the y direction corresponds to the left or right leg, respectively. The testicular region is defined by the following inequalities : -4.8 5 z 5 0 z 1% 100 >= 0

+

+

and

The volume of the genital region, including skin and testes, is 196 cma, and the mass is 194 g. The volume of both testes is 38.6 cma, and the mass is 37.1 g. About 23 cm3of the genital region is skin, a horizontal layer of thickness 0.2 cm and volume 7.2 cm3forming the horizontal base of the genital region in Fig. 13-1, and the frontal skin formed by the layer between the planes z

+ 1%+ 100 = 0

and z 3. 106y

+ 98 = 0

and bounded by

-4.65150

and

-(lO+$)~X510+

but outside the legs, i.e., and 'X

+ Y'

= -X

Z 10

58

/

APPENDIX B

Fig. B-1. Legs and male genitalia of phantom (Snyder el al., 1976).

This frontal skin has a volume of about 16 cm3.Thus, the skin of this portion of the genitalia has a mass of about 23 g. The mass of the region, exclusive of skin and testes, is about (194 - 37 - 23)g = 134 g. Occasionally, the dose to the larger mass of the genitalia minus skin may be useful as an approximation to the dose received by the t ~ tThis . larger region has a mass of 175 g.

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USAEC (1962). Civilian Nuelear Power, A Report to the President, 1962: Appendices Attached (U.S. Atomic Energy Commission, Washington). USAEC (1965). Estimated Growth of Civilian Nuclear Power, WASH-1055 (U.S. Atomic Energy Commission, Washington). USAEC (1967a). Sz~pplementlo Civilian Nuclear Power, A Report to ON President, 1962: Appendices Attacl~d(U.S. Atomic Energy Commission, Washington). USAEC (1967b). Forecast of Growth o j Nuclear Power, WASH-1084 (US. Atomic Energy Commission, Washington). USAEC (1970a). U.S. Atomic Energy Commission, Chart of the Atoms, Knolls Atomic Power Laboratory, General Hectric Company (Educational Relations, General Electric Company, Schenectady, New York). USAEC (1970b). Assumptions Used for E v a l d i n g the Potential Radiological Consequences of a Loss of Coolant Accident for Bdling Water Reactors, Safely Guide 3 (U.S. Atomic Energy Commission, Director of Regulatory Standards, Washington). USAEC (1970~).Potential Nwlear Power Growth Patterns, WASH-1098 (U.S. Atomic Energy Commission, Washington). USAEC (1971). Forecast o j Growth o j Nuclear Power, WASH-1139 (U.S. Atomic Energy Commission, Washington). USAEC (1974). Final Enwironmenld Stalement Relaled lo Constrmclion and Operation at Barnwell Nuclear Fuel Plant, Docket No. 50-332, p. V-15 (Division of Technical Information, U.S. Atomic Energy Commission, Washington). VOILLEQUE,P . G. AND FIX,J. J. (1975). "Transfer of airborne krypton-85 to vegetation," The hroble Gases, Moghissi, A. A. and Stanley, R. E., Eds. (U.S. Government Printing Office, Washington). WEAST,R. C. AND SELBY,S. M. (1971). Handbook o j Chemistry and Physics, 52nd ed. (Chemical Rubber Co., Clevebnd, Ohio). WHITMAN,M. J . , TARDIFE',A. N. AND HOFMANN, P. L. (1972). "U.S. civilian power cost benefit analysis," p. 475 in Peaceful Uses o j Alomic Enmgy, Vol. 2 (Uriited Nations, New York and International Atomic Energy Agency, Vienna). W F ~ I ~ J. NT , . (1968). Dose Arising j r m Inhalation of Noble Gases, CEGB Report RD/B/N-1274 (Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire, U. K.). W H I ~ NJ., T. (1973). "New values for epidermal thickness and their importance," Health Physics 24, 1. WIRSING,E., JR.,HATCH, L. P. AND DODGE,B. F. (1970). L020 Temperature Adsorption o j Krypton on Solid Adsorbents, BNL-50254 (Brookhaven National Laboratory, Upton, New York). YEH, S. Y. AND PETERBON, R. E. (1965). "Solubility of krypton and xenon in blood, protein solutions and tissue homogenates," J. Appl. Pliysiol. 20, 1041.

The NCRP The National Council on Radiation Protection and Measurements is a nonprofit corporation chartered by Congress in 1964 to: 1. Collect, analyze, develop, and disseminate in the public interest information and recommendations about (a) protection against radiation and (b) radiation measurements, quantities, and units, particularly those concerned with radiation protection; 2. Provide a means by which organizations concerned with the scientific and related aspects of radiation protection and of radiation quantities, units, and measurements may cooperate for effective utilization of their combined resources, and to stimulate the work of such organizations; 3. Develop basic concepts about radiation quantities, units, and measurements, about the application of these concepts, and about radiation protection; 4. Cooperate with the International Commission on Radiological Protection, the International Commission on Radiation Units and Measurements, and other national and international organizations, governmental and private, concerned with radiation quantities, units, and measurements and with radiation protection. The Council is the successor to the unincorporated association of scientists known as the National Conmittee on Radiation Protection and Measurements and was formed to carry on the work begun by the Committee. The Council is made up of the members and the participants who serve on the fifty-four Scientific Committees of the Council. The Scientific Committees, composed of experts having detailed knowledge and competence in the particular area of the Committee's interest, draft proposed recommendations. These are then submitted to the full membership of the Council for careful review and approval before being published. The following comprise the current officers and membership of the Council : Officers President Vice President Secretary and Treasurer Assistant Secretary Assistant Treasurer

LAWRISTON S . TAYLOR E . DALETROUT W. ROGERNEY EUGENER. FIDELL HAROLD 0.WYCKOFF

Members

Honorary Members

EDGAR C. BARNES CABLB. BRAESTRUP AUSTINM. BRUES L. DUNHAM CHARLES D. EVANS ROBLEY PAULC. HODGES KARLZ. MORGAN EDITHH. QUIMBY SHIELDS WARREN

Currently, the following Scientific Committees are actively engaged in formulating recommendations:

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SC-1: Basic Radiation Protection Criteria SC-7: Monitoring Methods and Instruments SC-9: Medical X- and Gamma-Ray Protection up to 10 MeV (Structural Shielding Design) SC-11: Incineration of Radioactive Waste SC-18: Standards and Measurements of Radioactivity for Radiological Use SC-22: Radiation Shielding for Particle Accelerators SC-23: Radiation Hazards Resulting from the Release of Radionuclides into the Environment SC-24: Radionuclides and Labeled Organic Compounds Incorporated in Genetic Material SC-25: Radiation Protection in the Use of Small Neutron Generators SC-26: High Energy X-Ray Dosimetry SC-28: Radiation Exposure from Consumer Products SC-30: Physical and Biological Properties of Radionr~clides SC-31: Selccted Occupational Exposure Problems Arising from Internal Emitters SC-32: Administered Radioactivity SC-33: Dose Calculations SC-34: Maximum Permissible Concentrations for Occupational and Non-Occupational Exposures SC-35: Environmental Radiation Measurements SC-36: Tritium Measurement Techniques for Laboratory and Environmental Use SC-37: Procedures for the Management of Contaminated Persons SC-38: Waste Disposal SC-39: Microwaves SC-40: Biological Aspects of Radiation Protection Criteria SC-41: Radiation Resulting from Nuclear Power Generation SC-42: Industrial Applications of X Rays and Sealed Sources SC-43: Natural Background Radiation SC-44: Radiation Associated with Medical Examinations SC-45: Radiation Received by Radiation Employees SC-46: Operational Radiation Safety SC-47: Instrumentation for the Determination of Dose Equivalent SC-48: Apportionment of Radiation Exposure SC-49: Radiation Protection Guidance for Paramedical Personnel SC-50: Surface Contamination SC-51: Radiation Protection in Pediatric Radiology and Nuclear Medicine Applied to Children SC-52: Conceptual Basis of Calculations of Dose Distributions SC-53: Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Radiation SC-54: Bioassay for Assessment of Control of Intake of Radionuclides

h recognition of its responsibility to facilitate and stimulate cooperation among organizations concerned with the scientific and related aspects of radiation protection and measurement, the Council has created a category of NCRP Collaborating Organizations. Organizations or groups of organizations which are national or international in scope and

are concerned with scientific problems involving radiation quantities, units, measurements and effects, or radiation protection may be admitted to collaborating status by the Council. The present Collaborating Organizations with which the NCRP maintains liaison are as follows: American Academy of Dermatology American Association of Physicists in Medicine American College of Radiology American Dental Association American Industrial Hygiene Association American Insurance Association li\ American Medical Association @ /$ American Nuclear Society , jr, L b American Occupational Medical Association American Podiatry Association American Public Health Association American Radium Society American Roentgen Ray Society American Society of Radiologic Technologists American Veterinary Medical Association Association of University Radiologists Atomic Industrial Forum Defense Civil Preparedness Agency Genetics Society of America Health Physics Society National Bureau of Standards National Electrical Manufacturers Association Radiation Research Society Radiological Society of North America Society of Nuclear Medicine United States Air Force United States Army United States Energy Research and Development Administration United States Environmental Protection Agency United States Navy United States Nuclear Regulatory Commission United States Public Health Service

The NCRP has found its relationships with these organizations to be extremely valuable to continued progress in its program.

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The Council's activities are made possible by the voluntary contribution of the time and effort of its members and participants and the generous support of the following organizations: Alfred P. Sloan Foundation American Academy of Dental Radiology American Academy of Dermatology American Association of Physicists in Medicine American College of Radiology American College of Radiology Foundation American Dental Association American Industrial Hygiene Association American Insurance Association American Medical Association American Mutual Insurance Alliance American Nuclear Society American Occupational Medical Association American Osteopathic College of Radiology American Podiatry Association American Public Health Association American Radium Society American Roentgen Ray Society American Society of Radiologic Technologists American Veterinary Medical Association American Veterinary Radiology Society Association of University Radiologists Atomic Industrial Forum Battelle Memorial Institute College of American Pathologists Defense Civil Preparedness Agency Edward ~Mallinckrodt,Jr. Foundation Genetics Society of America Health Physics Society James Picker Foundation Nat.iona1 Association of Photographic MeuufacL~~em National Bureau of Standards National Electrical Manufacturers Association Radiation Research Society Radiological Society of North America Society of Nuclear Medicine United States Energy Research and Development Administration United States Environmental Protection Agency United States Public Health Service

To all of these organizations the Council expresses its profound appreciation for their support. Initial funds for publication of NCRP reports were provided by a

THENCRP

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grant from the James Picker Foundation and for this the Council wishes to express its deep appreciation. The NCRP seeks to promulgate information and recommendations based on leading scientific judgment on matters of radiation protection and measurement and to foster cooperation among organizations concerned with these matters. These effo& are intended to serve the public interest and the Council welcomes comments and suggestions on its reports or activities from those interested in its work.

NCRP Reports NCRP Reports are distributed by the NCRP ~ublications' office. Information on prices and how to order may be obtained by directing an inquiry to: NCRP Publications P.O. Box 30175 Washington, D.C. 20014 The extant NCRP Reports are listed below. NCRP Report No. 8

Title Control and Renwval of Radioactive Contamination i n Laboralories (1951) Reunnmendations for W a s k I)isposal of Phosphorus-32 and Iodine-131 for Medical Users (1951) Radiological Monitoring Methods and Instruments (1952) Recammendatirms for the Disposal of Carbon-14 Wastes (19531 Protection Against Betatron-Synchrotron Radialions Up To 100 MiUion Electron Volts (1954) Radioactive Waste Disposal in the Ocean (1954) Maximum Pemissible Bodg Burdens and Maximum Permissible Cbneentrations of Radionuclides in Air and in Water jor Occupational Exposure (1959) [Includes Addendum 1issued in August 19631 Measurement of Neutron Flux and Spectra for PhysS1caland Biological Applications (1960) Measu~ementof Absorbed Dose of Neulrons and of Mixtures of Neutrons and Gamma Rays (1961) Stopping Powers for Use wilh Cavity Chumbers (1961) A Manual of Radioactivity Procedures (1961) safe Handling of Radioactive Materials (1964) Shielding for High-Energy Electron Accelerator Installations (1964)

Radidion Protection i n Educalimal Instilutions (1966) Medicd X-Ray and Gamma-Ray Protection for Energies U p lo 10 McV-Equipment Design and Use (1968) Medical X-Ray and Gamma-Ray Protection for Energies U p 72

NCRP REPORTS

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to 10 MeV-Stmdural AhieLding Design and Evaluath (1970) Dental X-Ray Protection (1970) Radiation Protection i n Veterinary Medicine (1970) Precaulions in the Management of Patieds Who Have Received Therapeutic Amounts oj Radwnuclides (I 970) Prolection Against Neutron Radiation (1971) Basic Radiation Protection Criteria (1971) Protection Against Radiation From Brachytherapy Sources (1972) SpeciJication of Gamma-Ray Brachytherapy Saurces (1974) Radiological Paetors Affecting Decision-Making in a Nuclear Attack (1974) Review of the Current State of Radiation Protection Philosophy (1975) Krypton-86 I n the Atmosphere-Accumulation, Biological Significance, and Control Technology ( 1 975)

Binders for NCRP Reports are available. Two sizes make it possible to collect into small binders the "old series" of reports (NCRP Reports Nos. 8-31) and into large binders the more recent publications (NCRP Reports Nos. 32-44). Each binder will accommodate from five to seven reports. The binders carry the identification "NCRP Reports" and come with label holders which permit the user to attach labels showing the reports contained in each binder. The following bound aets of NCRP Reports are also available: Volume I. NCRP Reports Nos. 8, 9, 10, 12, 14, 16, 22 Volume 11. NCRP Reports Nos. 23, 25, 27, 28, 30, 31 Volume 111. NCRP Reports Nos. 32, 33, 34, 35, 36, 37 Volume IV. NCRP Reports Nos. 38, 39, 40, 41 (Titles of the individual reports contained in each volume are given above.) The following NCRP reports are now superseded and/or out of print: NCRP Report No. 1 2

Title X-Ray Protection (1931). [Superseded by NCRP Report No. 31 Radium Protection (1934). [Superseded by KCRP Report

No. 41 3 4

X-Ray Protection (1936). [Superseded by NCRP Report No. 61 Radium Protection (1938). [Superseded by NCRP Report No. 131

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5 6

7

11 13 15 17

18 19 20 21 24

26 29

Safe H a d i n g of Radioactive Luminous Compounds (1941). [Out of print] Medical X-Ray Protection u p lo Two Million Volts (1949). [Superseded by NCRP Report No. 181 Safe Handling of Radioacliw Isotopes (1949). [Superseded by NCRP Report No. 301 Maximum Permissible Amounts of Radioisotopes in the Hunlan Body and Maximum Permissible Concentrations in Air and Water (1953). [Superseded by NCRP Fkport No. 221 Protection Against R a d i a t i m ~from Radium, Cobalt-60 and Cesium-137 (1954). [Superseded by NCRP Report No. 241 Safe Handling of Cadavers Containing Radioactive Isotopes (1953). [Superseded by NCRP Report No. 211 Permissible Dose from External Sources of Ionizing Radialion (1954) i~lcludingMaximum Permissible Exposure to Man, Addendum to National Bureau of Standards Handbook 69 (1958). [Superseded by NCRP Report No. 391 X-Ray Protection (1955). [Superseded by NCRP Report No. 261 Regulation of Radiation Exposure by Legislative Means (1955). [Out of print] Protection Against Neutron Radiation Up fo 30 Million Electron Volts (1957). [Superseded by NCRP Report No. 381 Safe H a d i n g of Bodies Codaining Radioaelive Isotopes (1958). [Superseded by NCRP Report No. 371 Protection Against Radiations jrom Sealed G a m m Sources (1960). [Shperseded by NCRP Reports Nos. 33, 34 and 401 Medical X-Ray Prokclion U p to Three MiUion Volts (1961) [Superseded b y NCRP Reports Nos. 33,34, 35 and 361 Exposure to Radiation in an Emergency (1962). [Superseded by NCRP Report No. 421

The following statements of the NCRP were published outside of the

NCRP Report series: "Blood Counts, Statement of the National Committee on Radiation Protection," Radiology 63,428 (1954) "Statements on Maximum Permissible Dose from Television Receivers and Maximum Permissible Dose to the Skin of the Whole Body," Am. Jr. of Roentgenol., Radium Therapy and Nucl. Med. 84,152 (1960) and Radiology 75,122 (1960) X-Ray Protection Standards for Home Television Receivers, Intenam Stale ment of the National Counnnnlon Rudiation Protection and Measurements (National Council on Radiation Protection and Measurements, Washington, 1968)

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Spe&$cdion of Units for Natural Uranium and Natural Thorium, (National Council on Radiation Protectiion and Measurements, Washington, 1973)

Copies of the statements published in journals may be consulted in libraries. A limited number of copies of the last two statements listed above are available for distribution by NCRP Publications.

INDEX Absorption a t ambient temperature, 40 Charcoal, 40 Molecular sieves, 40 Adsorption on charcoal, 40,41 Ambient temperatures, 40 Cryogenic temperatures, 41 Atmospheric dispersion calculations for 86H, 19 Eatimate of population dosage for the world, 19 Global scale dilution, 19 Maximum annual average concentration near a fuel processing plant, 21 Maximum concentration, 19 Maximum credible 24-hour concentration near a fuel processing plant, 21 World populstion weighted 8 q r concentrations, 20 Atmospheric krypton, 18 Atmospheric volume, 16 Biological properties of krypton, 4 Anesthetic action, 4 Blood solubility, 4 Diffusion in tissue, 4 Lipid solubility, 4 Radioprotection action, 4 Biological significance of absorbed dose, 36 Carcinogenic effects, 36 Genetic effects, 36 Calculation of dose from 86Kr in the

Clathrate precipitation 2, 45 Concehtrationa of 86Kr measured in northern hemisphere, 33 Cryogenic adsorption, 41 Cryogenic distillation, 44 Deposition of 8bKr on the soil, 17 Dose from bremsstraMung, 25 External bremsstrahlung, 26 Internal bremstraMung, 25 Dose from 85Kr in the airways of the lungs, 31 B~~~marrow, 31 Lung, 31 Ovaries, 31 Testes, 31 from photons produced in a semiinfinite cloud, 22 Dose rate, 22, 29, 30 Dose rate to active bone marrow, 22, 29,30 Dose rate to bone, 22, 29, 30 Dose rate to gonads, 22, 29, 30 Dose rate to lungs, 22,29, 30 Dose rate to skin, 22, 29, 30 Dose rate to soft tissue of the body, 22, 29, 30

Dose rate to subcutaneous tissue, 22, 29,30 Dose rate from beta rays in an infinite cloud, 28 Dosimetry, 22 Environmental dispersal of 8sKr, 16 Absorption by the soil, 18 Adsorption onto particulate matter, 18 Atmosphere, 19 Deposition through adsorption on particulate matter, 17 Dry deposition, 17 Ocean, I6 Waehout of a'%, 17

body, 25 Formulae, 25 Calculation of long-term air concentrations, 60 Carcinogenic effects, 36 Carcinogenic effects on skin, 38, 46 Chemical properties, 1 Chemical reactions, 2 Clathrate formation, 2 Ionic or covalent bonding, 1 Solubility, in nonpolar solvents, 2

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INDEX

Exposure t o the public from stimulation of natural gas, 8 Exposure to 9 Exposure to tritium, 9 Future power requirements, 10 United States energy requirements, 11 World energy requirements, 11 Genetic effects, 36 Hazards in BsKroff-gas removal systems, 41, 44, 45 Interaction of ionizing and ultraviolet radiation, 38,46 Induction of skin cancer, 38 Interim holdup of xenon and krypton, 41 Krypton concentration in air, 16 Krypton in vegetation, 18 86Kr generation and inventory to the year U)o,14 Nuclear reactor mix, 14 World nuclear electric power capacity, 14 86Kr inventory, 10 86Kr releases, 10 86Kr removal from waste gases, 40 Adsorption a t ambient temperatures, 40 Clathrate precipitation 46 Cryogenic adsorption, 41 Cryogenic distillation, 44 Permselective membranes, 45 Selective absorption, 44 Mantle rock capacity for krypton, 18 Mass of K r in atmosphere, 16 Mass of Kr in the mixed layer of oceans, 16 Molecular sieves, 40, 41 Ambient temperature, 40 Cryogenic temperature, 41 Natural sources of 86Kr, 6 Neutron capture reactions, 5 Spontaneous and neutron-induced fissions, 5 Steady-state environmental inventory from natural sources, 5 Nuclear reactor mix, 14 Fast brecder reactor, 14 Light water reactor, 14 Liquid metal fast breeder reactors, 15 Thermal converter reactor, 14

Nuclear weapons testing and production of S 6 K r , 5 Current B6Krinventory, 5 Integrated generation, 5 86Kr generation from U.S. plutonium production, 6 Specific yield of abKr, 5 Underground weapons tests, 6 Off-gas treatment processes for 42 Ostwald coefficient, 25 Peaceful uses of nuclear explosives, 8 Gas well stimulation, 8 Project plowshare, 8 Permselective membranes, 45 Phantom description, 57 Physical properties of krypton, 2 Atomic number, 2 Atomic radius, 2 Atomic weight, 2 Boiling point, 2 Critical point, 2 Demity, 2 Isotopic natural abundance, 2 MeItiog point, 2 Radioactive isotopes, 2 Triple point, 2 Power reactors, 7, 14 Projected carcinogenic effects, 37 Projected genetic effects, 36 Projected 86Kr concentrations, 32, 34 Projected nuclear electric power capacity, 47 Projected skin dose, 46 Projected world population dose commitments, 36 RRd bone marrow, 35 Skeleton, 36 Skin, 35 Properties of Kr and S6Kr, 1 Biological properties, 4 Chemical properties, 1 Physical properties, of krypton, 2 Radiological properties, 3 Radioactive isotopes of krypton, 2 Radiological properties of 86Kr, 3. Decay scheme, 3 Endpoint energies, 3 Fission yields, 4 Half-life, 3

INDEX Radiological properties of a K r (Conlind)

Mean /? energies, 3 Primary radiations, 3 Secondary radiations, 3 Recommended interim policy for reactor releases, 46 Recommended policy for releases from fuel reprocessing plants, 46 Reprocessing plants, 7, 21 Release rate of s6Kr, 7 Maximum annual average 8'Hr concentration, 21 Maximum credible 24-hour 86Kr concentrations, 21

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Selective absorption, 44 Skin dose equivalent rates due to 86Krin the atmosphere, 34 Soil-krypton interaction, 18 Sources, of S6Kr,5 Natural sources, 5 Naval propulsion reactors, 8 Nuclear weapons testing and production of e%-, 5 Peaceful uses of nuclear explosives, 8 Power reactors, 7 Reprocessing plants, 7 Ultraviolet radiation, 38, 46 Washout of S6Kr, 17 Washout coefficient, 17