Plutonium Dispersal by Accidental or Experimental Low-Order Detonation of Atomic Weapons

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LOS ALAMOS SCI ENTlFlC LABORATORY University of California by Accidental or Experimental Low-Order Detonation of Atomic Weapons ATOMIC ENERGY COMMISSION

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authorr and doeta not neceeaorily reflect the opinions or Hews of the Lo8 Alamos Scieuttflc Laboratory. Printed fn USA. Price $2.00. Available from the Clearinghouse €or Federal ScientLfic and Technical Information, National Bureau of standards, United lstates Department of Commerce, Springfield, Virginia

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UC-41, HEALTH AND SAFETY 10s ALAMOS SCI ENTIFK LABORATORY University of California Report written: December 1955 Revised edition distributed: February 1966 by Accidental or Experimental Low-Order Detonation of Atomic Weapons

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Accidental or exper imental detonation of 8tomic weapons that contain plutonium under conditions such that the degree of critical it y produced is Insignificant may create an imme - diate and a residual or delayed plutonium health hazard. Uranium, which is also consistently present, i6 not a radioactive health hazard. The immediate hazard is associated with the inhalation of.plutonium during cloud passage and on the basis of theoretical considerations appears to be relat iv ely insignificant. The delayed hazard results from residual plutonium deposited in the fall - out pattern, which may produce chronic contamination over a long period of time. The magnitude of the residual hazard is not easily evaluated on a theoretical basis, since it depends on a number of parameters which are not readily established. curves for maximum allowable air concentrations as a function of time of exposure, based on the assumption of a maximum permissible level of 0.008pc of plutonium inthe lung and a maximum permissible total body level of 0.5Fg, have been developed. These curves may be quite uae ful in assessing the magnitude of the immediate and residual hazards. Suggestions are made as tothe course of action that should be followed in the event of an accidental detonation of the type under

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2. General Statement of the Problem 2.1 Immediate or acute hazard 3. General Considerations of the Fall-Out and Con4. Biological Considerations of Maximum Permissible 4.1 Biological fate of Inhaled radioactive 4.2 Calculation of the maximum permissible level in the lung 4.3 Calculation of maximum permissible level for total body burden 4.4 Calculation of the maximum permissible level in air based on lung exposure 4.5 Calculation of the maximum permissible level in air based on maximum permissible total body burden 5.2 Course of action indicated by existing information in the event of accidental or experimental low order detonations 6. Proposals for Experiments to Evaluate Certain

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tion pattern as might be expected from Sutton's formula, assuming release at ground level and wind speed of 11 mph Fig. 2 General model for the fate of radioactive particles (0.5-10 u) in the lung Fig. 3 Maximum permissible air concentration as a function of time of continuous exposure using the lung as the critical organ Fig. 4 Maximum permissible air concentration as a based on maximum permissible level of 0.5 Crg for the total body 25 Fig. 5 Maximum permissible air concentration as a function of time of continuous exposure assuming the more conservative of the two limiting conditions F i g . 6 Change in total body burden as a function of time of continuous exposure using maximum permissible amount in the lung as t h e limiting factor for air concentration

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Recent shots fired at the Nevada Test Site (NTS) enable a preliminary analysis of the hazards from accidental or experimental detonation of atomic weapons when little or no fission occurs, i.e.8 when the yield is essentially that of the high explosive component. The health hazard arises from the plutonium which may be present. Uranium, although cons is tent ly present, affords no radiological health hazard i n the quantities and degree of dispersion involved because Of its very much lower specific activity and because of its behavior in biological systems. 2 . General Statement of the Problem The majority of the plutonium undoubtedly will be conThe heatverted tothe oxide by the heat of the explosion. of the explosion and the pyrophoric nature of plutonium metal may result i n the generation of a n oxide fume consist - ing of a high relative percentage of fine particles, The oxide produced will be carried out in all directions by the shock front and taken up in the cloud which will produce a fall - out condition in the immediate vicinity and downwind from the point of detonation. The fall - out condition will produce two different types of plutonium hazard, (1) fmmediate or acute, and (2) residual.

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2.1 Immediate or acute hazard Within the limits of the fall - out pattern tAClUding the downwind vector, there may be high plutonium concentfations (in fine particulate form) inthe air for several minutes after the detonation. This high concentration of plutonium i n the air rill create an immediate or acute plutonium inhalation hazard t o anyone caught in or entering the area before all of the particulate Plotter bas settled tothe ground. As the majority of the plutonium suspended In the air map be primarily in the tom of Ziae insoluble plutonium oxide particles, radiation exposure of the lung probably rill be the primary hazard. The magnitude of t h e Immediate hszard rill dopond on the plutonium concentration per unit volume of air, .the respiratory rate of the lndivi dual, the time the individual is in the fall - out, and t o aOme extent the size distribution of the particles carrying the radioactive material. Settling of the ruspended matter inthe fall-out pat - tern rill resu2t in a primary area o f surface contamination essentially the mbpe m d rize of the original fall - out plane. This residual contamination rill result In a potential plutonium health hazard to persons living or

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working in the area for a rehtlvely long time after the detonation. It should be emphasized strongly that any omOUnt of plutonium deposited on the surface constitutes no hazard rhataoever ao long as it remains deposited. actual plutonium hazard to persons living or workfng In the contaminated area is, therefore, directly dependent on the amount of plutonium on the surface and the fraction of the surface contamination which is subsequently disturbed and rcsuspended in a manner which will enable it to gain entrance Into the body. Plutonium may enter the body in three different m y S , by ingestion, by inhalation, and through -f r e s h breaks and abrasions of the s k i n surface. Since tbe absorption of plutonium from the &t i s extremely amall compared to absorption from the lung (about 0.0032 of the ingested dose from the gut, compared to 2-10% of the inhaled dose from the lung), and since the possibility o f contaminated cuts and wounds is l o w , the residual hazard to persons living or working in P contaminated area is primarily one of inhalation. The inhalation hazard produced in such a contaminated area is, therefore, directly dependent on the plutonium concentration in the area, the time one remains i n the area, and the degree of disturbance or resuspension of the dcposited plutonium into the atmosphere. Especially is the above

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statement true for persons entering and working in the area, performing operations that produce considerable dust. In the case of persons living indefinitely in such a contaminated area, contamination and Ingestion of food and water could become a -11 contributing factor to the hazard. As mentioned earlier, an accidental or experimental explosion of the type being considered w i l l result in plutonium being carried out in a l l directions by the shock front and taken up into the cloud which rill produce a f a l l - out condition in the immediate vicinity and downwind from the point of detonation. An idealized picture of the f a l l - out and contamination pattern might be expected to be similar to that shown in Figure 1. This illustration was modeled after a similar one depicted in "Meteorology and Atomic Energy"* and represents t h e situation as I t might be expected to occur, based on Sutton's fonnulrr, applied to the instantaneous condition, assuming release at ground level and a rind 8peed of 11 mph. *Report AECU 3066, July 1955, for Sal0 by the Superintendent of DOctaments, U. 9. Government Printing Office, Washington

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tern may be far from the Idealized picture given In Figure 1, which requires the assumption t bt the fall - out of the particulate matter inthe cloud is in accordance with Stokes: l a w . I f # however, much of the plutonium oxide is formed as a fume, a high relative percentage of particles rill be too fine to obey Stokes' law, and local turbulence, small-scale eddy motions, 8nd effects of local terrain map completely dominate the gravitational settling. The above cond ft ions ray result In the deposition of relatively high concentrations of plutonium a t much greater distances from the point of detonation than would be expected on the basis of the The length and the shape of the downwind vector may be expected to be dependent on the specific meteorological conditions at the time of the detonation,the particle size distribution, and the height to which the cloud rises. The amount of plutonium per unit volume of air during the fall - out and the amount of plutonium contamination deposited per unit of marface area would be expected to be directly proportion alto the amount of plutonium involved in the detonation, md Inversely proportional tothe dilution fact o r which might be expected t o depend on the size of the detonation 8nd the specific meteorological co adit fons.

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The primary surface contamination pattern may be spread and diluted with time in relation to the degree of disturb - ance of the surface area. Yeteorological conditions and the mount of personnel activity in the area will be the pri nci - pal contributing factors to the disturbance of the surface and, thus, tothe spread of the contamination field. Specific answers as tothe magnitude of air and surface contamination as a fu qc tion of distance from the detonation and the effect of wind, etc., on the size and 6pread of the contaminated area can best be obtained by experimental firing of high explosives with plutonium under a variety of antic - ipa ted meteorological and other applicable conditions. 4. Biological Considerations of Maximum Permissible 4.1 Biological fate of inhaled radioactive particles As indicated previously,the principal hazards involved in the situation being discussed are respiratory. It is necessary, therefore, to give careful consideration to the biological fate of inhaled radioactive particles. The fate of particulates In the lungs is obviously an extremely complex subject and only the general aspects which are essential to the present problem will be considered. Atthe Harriman Tripartite Conference held in September

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of 1954, representatives of the United States, Canada and Great Britain, on the b a s i s of the best available experimental information, devised a general model for the fate of radioactive particles in the lung. model adapted to the problem of inhaled soluble and insoluble particles of plutonium of 10 microns or less, which is t h e optimum range for the production of a health hazard. ing to t h i s figure, wben.100 particles are inhaled, 25 are exhaled without deposition on the respiratory surfaces. vio us ly, these are of little or no concern to the question of the production of a health hazard. Of the 75 particles that deposit on the respiratory surfaces, 50 deposit out in t h e bronchial tree and are worked up and out of the bronchi by t h e ciliary epithelium and swallowed, passing out of the body v i a the gut. The half-time of elimination of these 50 particles from the bronchial tree is estimated at about 18 hours. Twenty-five of t h e original 100 particles are deposited on the alveolar surfaces of the lung, where a0 ciliary epithelium exists. If these particles are insoluble (which is the ea88 in the problem under consideration), 15 (15% of the originally inhaled dose) are phagocytized and otherwise removed up the bronchial tree and eliminated from the body via the gut with an elimination half-time estimated to be about 140 days. The remaining 10 particles (10% of the Figure 2 shows the general

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originally inhaled dose) are absorbed or otherwise taken from the lung into the blood stream where they contribute t o the systemic or total body burden, about 80% of which is fixed in the skeleton. The absorption half-time of these 10 particles is estimated to be about 60 days. The above situation creates two different hazards, the first of which is the direct radiation hazard to the lung by the deposition of 75% of the originally inhaled dose, taking into account the respective abundances and the half-times of rhe three components of the elimination process. The second hazard i s that produced by absorption into the blood stream and subsequent deposition of 10% of the originally inhaled dose in the skeleton. On the basis of this model, it is possible t o calculate the magnitude of these two hazards as & function of air concentration and time of exposure. It is fmperatlve, therefore, to know the plutonium air concentration during the fall-out period in order to assess the immediate bazlrrd produced by experimental or accidental one-point detonation of the weapons under consideration, and it is likewise imperative to know the chronic plutonium air concentration created in the environment of persons working and living in the contaminated amp, i n order to amess the residual or long-term hazard.

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4.2 Calculation of the maximum permissible level in the If the lung itself I s considered to be the critical organ, the maximum permissible level (MPL) In the lung Will depend upon the concentration of the radioactive aPateria1 per gram of tissue and the effectiveness of the radiating particle so that the dose will not exceed 0.3 rem/week under continuous exposure. *The information given in Handbook 52 must be used as the criteria for such a determination. The MPL is given by the following formula: where q - total uc of activity allowable RBE - effectiveness of alpha particles - 20 b = fractional absorption of energy - 1 for = fraction in critical organ of that in total body = 1 in the present case '*National Bureau of Standards Handbook 52, baarch 20, 1953, for sale by t h e Superintendent of bcuments, Washington

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’ mass. This value is, therefore, the maximum permissible level for continuous exposure to insoluble Pu239 over a lifetime. The above value is probably extremely conservative in that continuous exposure is assumed and the RBE of the alpha PaFtiCleS is as sued to be 20, which from present experimental Information appears to be too large by as much as a factor of 4.3 Calculation of maximum permissible level for total body The presently accepted YPL for deposition of plutonium in the total body …