Summary of Past Criticality Accidents

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

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

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