A Review of Criticality Accidents A Review of Criticality Accidents

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B. BARE AND REFLECTED METAL ASSEMBLIES 1. Los Alamos Scientific Laboratory, 21 August 194537,44 Plutonium core reflected with tungsten carbide; single excursion; one fatality, one significant exposure. 2. Los Alamos Scientific Laboratory, 21 May 194637,44 Plutonium core reflected with beryllium; one fatality, seven significant exposures. Two accidental excursions occurred with the same core and were, in several respects, quite similar. The core consisted of two hemispheres of δ-phase plutonium coated with 5 mils of nickel. The total core mass was 6.2 kg; the density was about 15.7 g/cm 3 . 74 In the first accident, a critical assembly was being created by hand stacking 4.4 kg tungsten carbide bricks around the plutonium core. Figure 41 shows a reenactment * of the configuration with about half of the tungsten blocks in place. The lone experimenter was moving the final brick over the assembly for a total Figure 41. Plutonium sphere partially reflected by tungsten-carbide blocks. * The Los Alamos National Laboratory archives include some data and comments about a rerun performed 2 October 1945 to determine the radiation dose received in the accident of 21 August 1945. The yield of the rerun was about 6 × 10 15 fissions, but the prompt critical state was not reached. The maximum reactivity of the system during this experiment was about 60 ¢ above delayed criticality.
eflector of 236 kg when he noticed from the nearby neutron counters that the addition of this brick would make the assembly supercritical. As he withdrew his hand, the brick slipped and fell onto the center of the assembly, adding sufficient reflection to make the system superprompt critical. A power excursion occurred. He quickly pushed off the final brick and proceeded to unstack the assembly. His dose was estimated as 510 rem from a yield of 10 16 fissions. He died 28 days later. An Army guard assigned to the building, but not helping with the experiment, received a radiation dose of approximately 50 rem. The nickel canning on the plutonium core did not rupture. In the second accident, the techniques involved in creating a metal critical assembly were being demonstrated to several people. The system consisted of the same plutonium sphere reflected, in this case, by beryllium. The top and final hemispherical beryllium shell was being slowly lowered into place; one edge was touching the lower beryllium hemisphere while the edge 180° away was resting on the tip of a screwdriver (Figure 42). The person conducting the demonstration was holding the top shell with his left thumb placed in an opening at the polar point. The yield of this excursion was 3 × 10 15 fissions; again, there was no rupture of the nickel canning. The eight people in the room received doses of about 2100, 360, 250, 160, 110, 65, 47, and 37 rem. The man who performed the experiment died nine days later. The results of fission rate calculations in this sphere, as a function of time for several values of excess reactivity, are shown in Figure 43. Figure 44 represents the total number of fissions to be expected as a function of time for the same excess reactivities. These data are applicable to both accidents because the difference in reflector material has only a small effect on the neutron kinetics. In the first excursion, if the excess reactivity did not exceed 15 ¢, the assembly must have been together for several seconds, which is not unreasonable. In the second event, the experimenter was better prepared to disassemble the material, and it is thought that this was done in a fraction of a second, perhaps
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LA-13638 Approved for public releas
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A Review of Criticality Accidents 2
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PREFACE This document is the second
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Tom Jones was invaluable in generat
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C. OBSERVATIONS AND LESSONS LEARNED
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FIGURES 1. Chronology of process cr
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51. MSKS and assembly involved in t
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A REVIEW OF CRITICALITY ACCIDENTS A
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3 Black Sea Baltic Sea Obninsk Norw
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North Atlantic Ocean Irish Sea Wind
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1. Mayak Production Association, 15
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time of the accident. However, the
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determined by a radiation control p
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consequences of this accident, the
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Figure 10. Drum in which the 1958 Y
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The entire plutonium process area h
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During the next shift, radiation sa
Page 37 and 38: 9. Siberian Chemical Combine, 14 Ju
Page 39 and 40: The accident investigation determin
Page 41 and 42: 10. Hanford Works, 7 April 1962 18,
Page 43 and 44: heater and stirrer were turned off
Page 45 and 46: vessel 64-A was added. The dissolut
Page 47 and 48: additional reflection afforded by t
Page 49 and 50: 15. Electrostal Machine Building Pl
Page 51 and 52: 16. Mayak Production Association, 1
Page 53 and 54: ased on a radiation survey, that th
Page 55 and 56: 0.5 m 0.5 m 0.5 m 0.5 m 3.0 m 1.4 m
Page 57 and 58: The investigation identified severa
Page 59 and 60: 19. Idaho Chemical Processing Plant
Page 61 and 62: 20. Siberian Chemical Combine, 13 D
Page 63 and 64: To Glovebox 6 7 8 6 From Glovebox 6
Page 65 and 66: on a 0.4 m square pitch grid. The b
Page 67 and 68: competing reactivity effects proved
Page 69 and 70: Figure 35. The precipitation vessel
Page 71 and 72: B. PHYSICAL AND NEUTRONIC CHARACTER
Page 73 and 74: Material Fissile Mass: Fissile mass
Page 75 and 76: 235 U Spherical Critical Mass (kg)
Page 77 and 78: Table 10. Accident Fission Energy R
Page 79 and 80: • Accidents in shielded facilitie
Page 81 and 82: • Senior management should be awa
Page 83 and 84: Table 11. Reactor and Critical Expe
Page 85 and 86: 3. Oak Ridge National Laboratory, 2
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Page 91 and 92: 3. Los Alamos Scientific Laboratory
Page 93 and 94: At the equatorial plane, the two ha
Page 95 and 96: Figure 48. The Los Alamos Scientifi
Page 97 and 98: Figure 50. Burst rod and several se
Page 99 and 100: On 11 March 1963, the facility chie
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Page 103 and 104: 14. Aberdeen Proving Ground, 6 Sept
Page 105 and 106: completed the construction of the l
Page 107 and 108: C. MODERATED METAL OR OXIDE SYSTEMS
Page 109 and 110: 63,65,66, 67 4. Chalk River Laborat
Page 111 and 112: 7. Centre dÉtudes Nucleaires de Sa
Page 113 and 114: a technician prescribing the loadin
Page 115 and 116: the room to drain the water out of
Page 117 and 118: In the final experiment, the critic
Page 119 and 120: 3. Los Alamos Scientific Laboratory
Page 121 and 122: III. POWER EXCURSIONS AND QUENCHING
Page 123 and 124: Figure 64. Energy model computation
Page 125 and 126: References 1. Stratton, W. R. A Rev
Page 127 and 128: 50. Paxton, H. C. “Godiva Wrecked
Page 129 and 130: 92. Stone, R. S., H. P. Sleeper, Jr
Page 131 and 132: criticality accident: The release o
Page 133 and 134: prompt criticality: State of a fiss
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5. Los Alamos Scientific Laboratory
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9. Siberian Chemical Combine (Tomsk
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13. Siberian Chemical Combine, 2 De
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15. Electrostal Machine Building Pl
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19. Idaho Chemical Processing Plant
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21. Novosibirsk Chemical Concentrat
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