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.
The â€oeB― virus (strain no. 1) was isolated from the spleen and central nervous system of patient B and maintained since the original isolation in 1932 by serial passage in rabbits. The virus is extremely pathogenic for rabbits by most routes of inoculation. Following intracutaneous injection, a hemorrhagic necrotic area develops around the site of inoculation. About one to two days before paralysis occurs, most rabbits exhibit a tendency to bite the local lesion (Sabin and Wright, 1934). The present study was undertaken to compare the sus ceptibility of Syrian hamsters exposed by various routes to the rabbit-adapted strain and mouse-adapted strain (Reagan et al., 1952) of the virus. METHODS
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