Date: 5 April 1968

Location: VNIITF, Chelyabinsk-70, Chelyabinsk, Russia, USSR

Type of event: criticality accident with uranium assembly

Description:

A criticality accident occurred with an assembly comprised of a highly enriched uranium sphere (90% U-235) with a polyethylene-filled cavity in the center, all to be surrounded by a natural uranium reflector. Two experimenters were conducting an experiment comparable to one conducted earlier in the day with no polyethylene in the core cavity, erroneously expecting little difference in the system performance. While lowering the upper hemisphere of the outer reflector, the system became critical and produced high power readings, prompting the emergency system to lower the lower hemisphere of the outer reflector, ending the excursion. The experimenters called for help and completed dose estimates. The individual closest to the assembly received a dose of 2000 to 4000 rem and died 3 days later; the other received a 500-1000 rem dose and died 54 days later.

Consequences: 2 fatalities.

References:

• McLaughlin, Thomas P., Shean P. Monahan, Norman L. Pruvost, Vladimir V. Frolov, Boris G. Ryazanov, and Victor I. Sviridov, May 2000, A Review of Criticality Accidents, 2000 Revision, Los Alamos National Laboratory (Los Alamos, NM), on line at CSRIC [http://www.csirc.net/docs/reports/la-13638.pdf].

© 2004, 2005 by Wm. Robert Johnston.
Last modified 14 September 2005.
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