Contamination Hazard from Accidental Non-Critical Detonation of Small Atomic Devices (Deleted)

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LOS ALAMOS SCIENTIFIC LABORATORY UNIVERSITY OF CALIFORNIA LA-2079-btL. This document consists of 3 m e s CONTAMINATION HAZARD FROM ACCIDENTAL OF SMALL ATOMIC DEVICES

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Two elements of risk my be involved i n the accidental non-critical detonation of atomic devices: (1) the immediate risk from inhalation of radioactive particles during cloud passage, and (2) the delayed or chronic risk frgm residual contamination. accidental detonation of maximum permissible levels at any distance. hazard seems t o be the limiting factor but use of the laboratory maximum permissible surface contamination level of 0.07 pc/M (1p g Pu/$) as the maximum acceptable limit of risk seems unrealistic. tory maximum permissible surface level is a "good house keeping" value related t o continuous operation rather than to isolated incidents and has no basis i n terms of the actual health hazard. Because of operati ve factors of resuspension and attenuation of surface radioactivity, ry 7 pc of alpha activity/$ (100 pg F'u/$) would seem t o be a more realistic value. A comparison of the relative contamination hazard from accidental detonation of the1,U The immediate hazard from type weapons prcibably would not exceed The chronic o r delayed

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weapon is l : l / h : l / 5O, respectively. The area of risk from an accident involving t h e core containing plutonium may not be too great t o cope with realistic Initial maximum permissible level for surface contamination. The area of concern in this case will probably be within 500 feet of the point of accident. Using the criteria of a relative hazard of 50 and a n allowable ground contamination of 5000 p g U235/M2, the area of concern will only be decreased by a factor of 4to6 (<25O feet from the point of detonation) for a substituted within this area can be effectively reduced by such practical procedures as washing down surfaced areas with fire hoses and plowing and revegetating unsurfaced areas. U235 core. The hazard

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2. General Statement of t h e Problem 7 2.1 Immediate o r acute hazard 2.2 Residual or chronic hazard Breaks and abrasions of the skin 4. Basis f o r and Calculation of Maximum Permissible Levels 4.1 Maximum permissible body burden Comparison of Hazard from Pu 239, U235 and U Maximum permissible concentrations inair 6 . htaluation of t h e Absolute Hazard from Fissionable 6.1 The immediate hazard 6.2 Chronic or delayed hazard 6.2.1 The surface tolerance ccmtarnination level for continuous exposure a s applied t o laboratory working surfaces Hazard from breaks and abrasions of the 6.2.3 Hazard from ingestion 3 1 6.2.4 Hazard from inhalation 33 0. ~ on clu a ions

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Maximum Permissible Body Burden f o r Plutonium and Uranium Based on t h e Gut, Lung and Skeleton as Critical Organs. Factors Required f o r Comparison of Relative Comparison of Relative Hazard of Various Correlation of Surface Activity with Acute Inhalation Dose during Cloud Passage. Maximum Permissible Initial Surface Contamination Levels under Various Conditions. Fig. 1 hximum permissible air concentrations as a function of time of exposure over a period Fig. 2 The relation between max’mum permissible lung burden and continued inhalation of a changing

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Potential application of small atomic devices planning necessitates an analysis of the fission able material contamination hazard associated with accidental detonation of the weapon under conditions such thE t the degree of critical it y produced is insignificant. Insignificant critical it yin this ca ~ emeans that the fission yield is so small that it contributes essentially nothing to the overall energy release compared t o that produced by t h e high explosive com2. General Statement of t h e Problem If sufficient energy I s released Inthe accident t o vaporize or Ignite the fission able material, a large fraction will be converted t o an oxide fume of relatively fine particle size. Much of the oxide may condense on or aggregate into larger particles. The radioactive material will be taken up inthe smoke cluud and produce afall - out condition inthe immediate vicinity, downwlnd from the point of origin.

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The shape of the fall - out pattern and the length of the downwind vector m y be expected t o depend on specific meteorological conditions a t the time of the accident, the particle size distribution and the height t o which the smoke cloud rises. material per unit volume of air during the fall-aut and the amount of radioactive contamination deposited per unit of surface area will be directly proportional tothe amount of radioactivity in the weapon, and inversely proportional to the dilution factor which i;l turn will depend on the height of the cloud (energy release), the meteorological conditions atthe time, and the distance from the point of accident. The amount of fission able Ideally, the shape of the primary fall - out plane would be a long cigar-shaped area extending downwind i n keeping with predictions based tamination pattern, as observed i n one-point detonation experiments a t In actuality, the primary fall-aut and conthe Nevada test site, i s far from the idealized picture since Sutton's fomla assumes that fall - out of particulates from the cloud is i n accordance with Stokes' law. Since the fissionable material i s converted t o an oxide fume, a high percentage of the particles appear t o be too small t o obey Stokes' law, and local turbulence, eddy currents and effects of local terrain dominate the gravitational settling. These conditions result in deposition of relatively higher concentration of radioactivity at much greater distances from the point of accident than predicted on the bases of the idealized model.

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I n the event the fission able material does not vaporize or ignite and burn t o the oxide, no fall - out condition will be produced and only a very local contamination problem will result. The fall - a utc on di tim will produce two different types of hazard: (a) immediate or acute, during cloud passage, and (b) residual or chronic as a result of surface deposition of the fissionable material. 3-1 Immediate o r acute hazard Within the limits of the fall - out area, including the downwind vector, there will be relatively high concentrations of fissionable material Inthe air for a few minutes after the accident. These concentrations might create an immediate or acute inhalation hazard t o anyone caught i n or entering the area before all of the particulate matter has settled tothe ground. Since the particles are composed of insoluble oxide, radiation exposure of the lung by inhalation and deposition of the radioactive particulates will be the primary hazard. The magnitude of the exposure will depend on the concentration of fission able material per unit volume of air, its specific activity, the respiratory rate of the individual, the time in the fall - out and t o some extent on the size distribution of the particles carrying the

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2.2 Residual or chronic hazard Residual contamination i n the fall-out plane may result In a potential radiation hazard t o persons living or working inthe area for a relatively long time after the accident. The primary surface contamination pattern will be spread and diluted with tfme in relation to the degree of disturbance of the surface area. Meteorological conditions (leaching from rainfall, wind dispersal, etc.) will be the major factor contributing tothe spread and dilution. Dilution with time will result in a much smaller hazard toa larger are alpha emitters,the radiation hazard will be essentially an internal one. Under these conditions, s h m l d bec emphasized strongly -that any amount -of alpha-active material deposited on the surface constitutes -no -hazard s o long as it remains deposited. The actual hazard t o persons---- inhabiting a n area contaminated with fission able material is, therefore, directly dependent on the fraction of the surface contamination which is subsequently disturbed and resuspended i n a manner enabling it t o gain entrance Into the body.

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no hazard when deposited on the surface of the unbroken skin because the particle ranges are less than the thickness of the cornified layer. Such materials are hazardous, therefore, only when indirect contact vith epithelial surfaces (i.e., surfaces of the gastrointestinal tract and lung) or when deposited directly in the tissues (i.e., inthe Fissionable materials m y contact or enter these damage-prone areas (a) by ingestion, (b) through -f r e s h breaks and abrasionsIn three ways: of t h e skin surface, and ( c ) by inhalation. Ingestion of fission able material will produce two potential radiatinuous passage of swallowed insoluble material (in this ca8e the total weight or a fraction of the gastrointestinal tract is taken as the (a) radiation of the gastrointestinal mucosa from con-

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critical tissue IPBSS), and (b) radiation of tissues and organs from absorption i n t o the blood and subsequent deposition. For Pu239 and isotopes of uranium the absorbed material deposits largely in bone, and the skeleton becomes the critical tissue ma88 which absorbs most of the radiation energy. soluble form is only about 0.0034 and of uranium about O.O5$. absorption of insoluble plutonium and uranium oxides from t h e gut would probably be about equal and would be even less t h a n t h e values The absorption of plutmium ingested i n for soluble forma . 7.2 Breaks and abrasions of the skin Fresh breaks and abrasions of the skin inflicted by contact with contaminated surfaces possibly could be contaminated. material could be absorbed into the blood from a contaminated wound and be deposited subsequently in the tissues, thereby contributing t o a systemic burden. If not absorbed, the msterial could remain a t the site of injury and produce radiation changes locally, as for example, A major part of both the immediate and residual hazard associated with the fall - aut of fission able material is associated with inhalation of the insoluble radioactive particles.

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The retention and elimination of insoluble particles by the lung is extremely complex and has been sham to be dependent on particle size, hygroscopicity, wetting, concentration, respiration rate, particle density, flocculation, solubility and chemical nature of the material inhaled. Because of the complexity of the problem, the lack of specific information and the need fora basis for calculating maxlruum permissible air concentrations, a general model for the fate of radiaactive particles in the lung has been proposed From limited experimental data on animals. According to the generalization, if 100 insoluble particles are inhaled, 254 are exhaled without deposition i n the respiratory system. Of the 7% deposited Inthe lung, 50 particles (50$ of the originally inhaled dose) deposit inthe upper bronchial tree and are eliminated by ciliary action and swallowed. be deposited on the alveolar surfacee. "insoluble" (as would be the case for uranium and plutonium oxides), 1 5 are phagocytized or otherwise removed up the bronchial t r e e and eliminated via the gut with an elimination half-time of about 6 - into the blood wlth a half-time of about 1 day where they contribute - tothe systemic burden. As far as the lung i s concerned, there would be essentially no difference i n the fate of particles of uranium The half-time of elimination i s The 25 particles remaining i n the lung are assumed t o If these particles are The remining 10 particle e pass through the alveolar wall

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and plutonium oxides. The above situation poses two different radiation hazards. first is the direct radiation of the lung by the deposition of 75% of the inbaled dose, taking into consideration the respective abundance8 and t h e half-times of the three components of the elimination process. The eecond is that produced by absorption of lo$ of t h e inhaled dose and eubeequent deposition of 70$ of t h e absorbed plutonium and 2C$ of the absorbed uranium inthe skeleton. values, it is possible to calculate the magnitude of the two hazards as a function of air concentration and time of exposure. On the basis of the above 4. Basis f o r and Calculation of Maximurn Permissible Levels of Exposure 4.1 Maximum permissible body burden The maximum permissible body burdens of internally-deposited radioactive Isotopes are derived by comparison with human experiences with Xray and radium. 0 . 3 r/wk of high energy X or gam rays is expected t o produce no bodily Injury if taken every week of one's life. I n the Utter case, past experience8 with the radium dial painters and with radium given for medical purposes has l e a d t o the conclusion that 0.1 pc of radium fixed in the body for a life-time will produce no significant Injury. The method of calculating internal tolerances for other substances is In t h e former case, human experience indicates that

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t o relate them theoretically to one or both of the above base llnes, taklng advantage of animal experimentation wherever poeeible. Inthe caee of alpha-emitting ieotopee that localize in bone, the comparison ie usually made vith radium, using the following formula taken from the Recolnmendatione of the International Commission on Radiological i n which q le the pc of the ieotope i n question in the total body when the radiation expoeure tothe ekeleton i e equivalent t o that delivered by 0.1 pc of fixed radium plus 5% of i t 8 daughter products, f2 le the fraction in the critical organ of that i n the total body, and rE(RBE)N is a weighted energy absorption term [weighted far average energy for all dieintegrations ( =E) i n Mev, the relative biological effectiveneee (RBE) i n rem/rad and for non-uniformity of distribution In the critical tie eu c me8 (N)]. I n calculating the dose t o moet eoft tieeuee, euch as the lung and the gut, the following expreeeion taken from t h e Recommendations of the Inter Dati om lCds ei on on Radiological Protection (2) is used:

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(g) In which the mterlal deposits, f2 = fraction in critical organ of total in body, andLE(RBE)N = the weighted energy absorption term. In this case, q becomes the pc of the isotope which will deliver 0.3 rem/wk tothe critical tissue mass of m (g). Using Equations (1) and/or (2) and the factors recamended inthe I. C . R. P. report (2), values for q may be calculated for t h e various isotopes based on the gae tro intestinal tract (Q) ,the lung (qL) and the bone (B) a8 the critical organs. These values are the same as TABLE I. Mtximum Permissible Body Burden for Plutonium and- -Uranium Based on the Gut, Lung and Skeleton as Critical Organs- * Half the value iven by uation (1) because of direct comparison of toxicity of Ra228 and Pu237 i n laboratory animals.

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Because of the very low absorption r a t e of plutonium and uranium from the gut and the rapid rate of …