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Criticality Accident Experience - doe-std-1128-98_ch10200
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DOE Standard Guide of Good Practices for Occupational Radiological Protection In Plutonium Facilities
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Criticality Alarms and Nuclear Accident Dosimetry - doe-std-1128-98_ch10202


DOE-STD-1128-98
Moe (1988) noted that for an excursion of >1018 fissions, dispersion of the fissile
material and the fission products would occur, resulting in heavy local
contamination and a subsequent high residual dose rate. This dose rate was
estimated at >1000 rad/h at 100 ft shortly after the burst and >10 rad/h at 30 ft an
hour after the burst. This is the basis for instructing workers to immediately run
from the work area when the criticality alarm is sounded. Seconds can save
significant dose, if not from the excursion itself, then from any residual radiation
that is in the area.
7.3.2
Summary of Past Criticality Accidents
Historically, there have been a total of five criticality accidents involving
plutonium (Stratton, 1967). Three of the accidents involved plutonium in solutions,
with the other two involving metallic forms. Three of the accidents involved early
research activities and the other two were plutonium-processing accidents.
Summaries of these two accidents follow as derived from Stratton (1967) or Paxton
(1966). No criticality accidents have occurred regarding mechanical processing,
storage of plutonium materials, or transportation of plutonium materials.
7.3.2.1
Los Alamos Accident - December 30, 1958
A nuclear criticality accident occurred on December 30, 1958, at the Los
Alamos Scientific Laboratory, killing one worker and overexposing two
other workers. The criticality occurred in a 225-gal, 38-in.-diameter
stainless steel tank, with a thick organic layer containing 3.27-kg
plutonium floating on a dilute aqueous solution of 60-g plutonium in 330
L. The tank was cylindrical and water-reflected. The tank contents were
stirred, mixing the contents into a criticality configuration.
Microbubbles, thermal expansion, and continued mixing of the tank
eliminated the critical configuration. The excursion consisted of a single
pulse of 1.5 x 1017 fissions. The operator near the tank received a lethal
dose of 12,000 rem (50%), while two workers who assisted the operator
received doses of 134 rem and 53 rem. The tank was supposed to have
only 0.125 kg of plutonium; however, a gradual accumulation of solids
during the 7.5-year operating history of the plant resulted in 3.27-kg
plutonium in the tank.
7.3.2.2
Hanford-Recuplex Plant Accident - April 7, 1962
On April 7, 1962, a criticality accident occurred at a multipurpose
plutonium-recovery operation at the Recuplex Plant, Hanford,
Washington. During a clean-up operation, about 46 L of solution
containing 1400- to 1500-g plutonium was directed into a 69-L glass
transfer tank that led to the criticality accident. The tank was spherical,
93% full, and unreflected. Solutions in the tank generally contain only a
fraction of a gram per liter; however, in this situation apparently the
solution was drawn from a sump through a temporary line that was being
used for cleanup. The excursion had an initial pulse of about 1016
fissions. Following this spike, the tank was supercritical for 37.5 hours
with the power level steadily decreasing (Stratton, 1967). The total yield
of the accident was about 8.2 x 1016 fissions distributed over a 37-hour
7-9


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