Health Physics Following a Nuclear Excursion

Abstract

On 26 March 1963 at approx. 0000 hours a nuclear excursion occurred in a shielded vault designed for critical assembly experiments. The excursion was estimated at 4 x lo1' fissions, and was followed by oxidation of the enriched uranium metal in the assembly. The fire was observed via closed circuit TV; later entry established that burning was limited to the assembly. Nearby combustibles did not burn or scorch.Disaster plans were immediately implemented to determine: (1) radiation exposures to personnel directly involved, (2) the possibility of recurring criticality and (3) the extent of release of radioactive materials to the Laboratory and to the off-site environment.Air and surface contamination levels were determined in the building housing the vault and at other points within the Laboratory perimeter. Air, vegetation, and soil samples, obtained within hours following the excursion, were analyzed for fission product and alpha activity fallout. Results indicated the release of small amounts of short-lived, high-yield gaseous fission products and their daughters. No detectable alpha activity was released to the environment.The maximum exposure to any of the four persons in the building at the time was 120 mrems penetrating gamma radiation. All neutron exposures were less than detectable limits, i.e. 50-mrem fast neutrons and 1-mrem thermal neutrons. Urinalyses, nasal wipes and thyroid scans were all negative, indicating no internal exposure.An air sample taken from within the vault 57 hr after the excursion showed levels of -2 x 1W6 pc/cm3 of short-lived fission products. Radioactive decay and changing the vault air reduced these levels to below MPC values. The air exhausted from the vault was filtered and scrubbed with caustic before release to the atmosphere.The initial vault entry was made to size up and-if necessary-to eliminate t t e possibility of a further excursion. The gross amounts of all fissile material were removed before decontamination operations were begun. The building, exclusive of the vault, was reoccupied 6 days after the incident.This incident reaffirms for us the value of carefully designed vault facilities for critical assembly work.

Preliminary report of the past and present uses, storage, and disposal of hazardous materials at the Lawrence Livermore National Laboratory

“…Air, vegetation, and soil samples obtained from within the Laboratory perimeter showed a small release of short-lived, high yield gaseous fission products and their daughters. No detectable alpha activity was released to the environment (Kathern 1963). The contamination inside the vault was cleaned up and fixed by painting the surfaces of the concrete .blocks.…”

Agricultural Implications of a Release of Fission Products from a Criticality Incident

“…The heat developed as a result of incidents of, say, lo1' fissions and over is certainly sufficient to make this possible and, as an example, in an accident involving enriched uranium at the Lawrence Radiation Laboratory on 25 March 1963, about 10 kg of metal were melted in an incident of just under 4 x lo1' fissions. (2) In such situations there is a likelihood not only of the release of the volatile fission products produced but also some of the fissile material itself, probably as oxide smoke particles.…”