Summary of Past Criticality Accidents - doe-std-1128-98

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

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