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

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UNIVERSITY OF CALIFORNIA fisbg b - / q 4 y f document consists of 41 pages This document contains restricted mittal or the disclosure of its Act of 1954. Its transperson is prohibited

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AEC Classified Technical Library AFSWC, Kirtland (Col. Karl Houghton) for: Everett Cox University of California Radiation Laboratory, Livermore Los Alamos Report Library

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Accidental or experimental detonation of small atomic weapons under conditions such that the degree of criticality produced is insignificant may create an immediate and a residual or delayed plutonium health hazard. hazard is associated with the inhalation of plutonium during cloud passage and on the basis of theoretical considerations appears to be relatively insignificant, 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 09 parameters which are not readily established. The delayed hazard Theoretical curves for maximum allowable air concentrations 8s a function of time of exposure, based on the assumption of a maximum permissible level of 0.008 uc of plutonium in the lung and a maximum permissible total body level of 0.5 rig, have been developed. These curves may be quite useful in assessing the magnitude of the immediate and reaction that should be followed in the event of an accidental detonation of the type under consideration. Suggestions are made as to the course of

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General Statement of the Problem 2.1 Immediate or acute hazard General Considerations of the Fall-Out and ConBiological Considerations of Maximum Permissible Biological fate of inhaled radioactive Calculation of the maximum permissible level in the lung Calculation of maximum permissible level for total body burden Calculation of the maximum permissible level in air based on lung exposure 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 31 6. Proposals for Experiments to Evaluate CertainSpecific Conditions 38

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tion pattern as might be expected from Sutton's formula, assuming release at General model for the fate of radioactive particles (0.5-10 p) in the lung Maximum permissible air concentration as a function of time of continuous exposure Maximum permissible air concentration as a function of time of continuous exposure based on maximum permissible level of 0.5 ugfor the total body 24 ground level and wind speed of 11 mpb 10 using the lung as the critical organ 22 Maximum permissible air concentration as a function of time of continuous exposure assuming the more conservative of the two limiting conditions 25 Change in total body burden as a function of time of continuous exposure using maximum permissible amount in the lung as the limiting factor for air concentration 28

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1. Intro duct io n----- Recent experiments atthe Nevada Test Site (NTS) have necessitated a preliminary analysis of the plutonium hazards associated with the accidental or experimental detonation of small atomic weapons under conditions such that the degree of critical it y produced is insignificant.In sign if i - cant critical it yin this case means that the fission yield is so low that it contributes essentially nothing tothe overall explosive yield compared t o that produced by the high explosive component of the weapon. 2. General Statement of t h e Problem- -.-- The majority of the plutonium undoubtedly will be converted t o the oxide by the heat of t h e explosion. The heat of the explosion and the pyrophoric nature of plutonium metal may result in the generation of a n oxide fume consist - ing of a high relative percentage of fine particles. oxide produced will be carried out in all directions by the shock front and taken up inthe cloud which will produce afall - out condition in the immediate vicinity and downwind from the point of detonation. produce two different types of plutonium hazard, (1) i m - mediate or acute, and (2) residual. The fall - out condition will

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2.1 Immediate or acute hazard- Within the limits of the fall-out pattern including the downwind vector, there may be high plutonium concentrations (in fine particulate form) in the air for several minutes after the detonation. This high concentration of plutonium in the air will create an immediate or acute plutonium inhalation hazard to anyone caught in or entering the area before all of the particulate matter has settled to the ground. in the air may be primarily in the form of fine insoluble A s the majority of the plutonium suspended plutonium oxide particles, radiation exposure of the lung probably will be the primary hazard. The magnitude of the immediate hazard will depend on the plutonium concentration per unit volume of air, the respiratory rate of the individual, the time the individual is in the fall-out, and to the radioactive material. Settling of the suspended matter in the fall-out pattern will result in a primary area of surface contamination essentially the shape and size of the original fall-out plane. This residual contamination will result in a potential plutonium health hazard to persons living or

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working in the area for a relatively long time after the hazard whatsoever so long as it remains deposited. actual plutonium hazard to persons living or working 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 resuspended in a manner which will enable it to gain entrance into the body. Plutonium may enter the body in three different ways, by ingestion, by inhalation, and through fresh breaks and abrasions of the skin surface. Since the absorption of plutonium from the gut is extremely small compared to absorption from the lung (about 0.003% of the ingested dose from the gut, compared to 2-102 of the inhaled dose from the lung), and since the possibility of contaminated cuts and wounds is low, the residual hazard to persons living or working in a 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 in the area, and the degree of disturbance or resuspension of the deposited 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 ares, contamination and ingestion of food and water could become a small contributing factor to the hazard. 3. General Considerations of the Fall-Out--and A s mentioned earlier, an accidental or experimental explosion of the type being considered will result in plutonium being carried out in all directions by the shock front and taken up into the cloud which will produce a fallout condition in the immediate vicinity and downwind from the point of detonation. An idealized picture of the fallout and contamination pattern might be expected to be similar to that shown in Figure 1. This illustration was modeled after a similar one dethe situation as it might be expected to occur, based on Sutton's formula, applied to the iqstantaneous condition, assuming release at ground level and a wind speed of 11 mph. of Documents, U. S. Government Printing Office, glashington Report AECU 3066, July 1955, for sale by the Superintendent

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In actuality, the primary fall-out and contamination pattern may be far from the idealized picture given in Figure 1, which requires the assumption that the fall-out of the particulate matter in the cloud is in accordance with Stokes' law. If, however, much of the plutonium oxide is formed as a fume, a high relative percentage of particles will be too fine to obey Stokes' law, and local turbulence, small-scale eddy motions, and effects of local terrain may completely dominate the gravitational settling. The above conditions may result in the deposition of relatively high concentrations of plutonium at 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 fallout and the amount of plutonium contamination deposited per unit of surface area would be expected to be directly proportional to the amount of plutonium involved in the detonation, and inversely proportional to the dilution factor which might be expected to depend on the size of the detonation and the specific meteorological conditions.

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The primary surface contamination pattern may be spread and diluted with time in relation to the degree of disturbance of the surface area. Meteorological conditions and the amount OP personnel activity in the area will be the principal contributing factors to the disturbance of the surface and, thus, to the spread of the contamination field. Specific answers as to the magnitude of air and surface contamination as a function of distance from the detonation and the effect of wind, etc., on the size and spread of the contaminated area can best be obtained by experimental firing of actual and tracer mock-up weapons under a variety of anticipated meteorological and other applicable conditions. 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 careiul consideration to the biological fate o€ 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 presect problem will be considered. A t the Harriman Tripartite Conference held in September

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of 1954, representatives of the United States, Canada and Great Britain, on the basis 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 the optimum range for the production of a health hazard. ing to this figure, when 100 particles are inhaled, 25 are exhaled without deposition on the respiratory surfaces. viously, 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 the bronchial tree and are worked up and out of the bronchi by the ciliary epithelium and swallowed, passing out of the body via the gut. Figure 2 shows the general The half-time of elimination of these 50 particles from the bronchial tree is estimated at about 18 hours. Twenty-five of the original 100 particles are deposited on the alveolar surfaces of the lung, where no ciliary epithelium exists. If these particles are insoluble (which is the case 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

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originally inhaled dose) are absorbed or otherwise taken from the lung into the blood stream where they contribute to 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 7556 of the originally inhaled dose, taking into account the respective abundances and the half-times of the three components of the elimination process. The second hazard is that produced by absorption into the blood stream and subsequent deposition of 10% of the originally inhaled dose in the skeleton. possible to calculate the magnitude of these two hazards as EL function of air concentration and time of exposure. On the basis of this model, it is It is imperative, therefore, to know the plutonium air concentration during the fall-out period in order to assess the immediate hazard 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 area, in order to assess the residual or long-term hazard.

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4.2 Calculation of the maximum permissible level in theIf the lung itself is considered to be the critical organ, the maximum permissible level in the lung will depend upon the concentration of the radioactive material 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 bIPL is given by the criteria for such a determination. The the following formula: total pc of activity allowable effectiveness of alpha particles = 20 fractional absorption of energy = 1 for energy in Mev = 5.16 for Pu fraction in critical organ of that in total body = 1 in the present case 3National Bureau of Standards Handbook 52, March 2 0 , 1953, for sale by the Superintendent of Documents, 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 particles is assumed 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 bodx The presently accepted MPL for deposition of plutonium in the total body is 0.5 pg (0.036 pc) . On the basis of the human experience resulting from the radium dial painting industry, the maximum permissible body burden for radium was set at 0.1 pc. The maximum permissible (total body) level for plutonium was established by estimating the amount of plutonium equivalent biologically to 0.1 vc of radium. estimation was based on the following considerations: monly used to designate that material which has been absorbed into the blood stream and subsequently deposited in the tissues, It does not, therefore, include unabsorbed material residing in the lungs or the gut.

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I n the above expression I6pLp, is the maximum permissible total body level for plutonium; ti ve biological effectiveness of plutonium when compared with radium in chronic experiments i n mice when radium and plutonium were injected in equal amounts; FPu is the fraction of plutonium retained in the mouse - 0.75; FRa is the fraction of radium retained in the mouse = 0.25 ; %a is the energy of the radium alpha particle ; FRna is the fraction of radon retained by the human - 0.5; FRnM is the fraction …