Database of radiological incidents and related events--Johnston's Archive

Kurtchatov SF-7 criticality accident, 1971

compiled by Wm. Robert Johnston
last modified 14 September 2005

Date: 15 February 1971

Location: Kurtchatov, Russia, USSR

Type of event: criticality accident with uranium


An experimental configuration was being used to test the effectiveness of reflector materials in a power reactor core. The experimental core used uranium oxide (20% U-235) fuel rods immersed in water to induce critcality. The test on 15 February used beryllium as a reflector, which was erroneously expected to behave similarly to an iron reflector previously used. Before all experimenters had arrived, a supervisor began adding water to the core tank without control rods actuated. The supervisor and another scientist saw a blue glow reflected from the ceiling at the same time neutron detection alarms sounded; they both left the room. The first excursion boiled some of the water into steam, expelling additional water from the tank; however, the water pump was still on and continued filling the tank, causing additional excursions before electricity supply to the pump was cut off about 6 minutes later. The two individuals in the room received localized doses to their feet of about 1500 rem; one was assessed a whole-body dose of 330 rem.

Consequences: 2 injuries.


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