INES-event
INES 2

REACTOR COOLANT LEAK DURING ON POWER REFUELLING DUE TO FUELLLING MACHINE DROP

During routine refuelling at full power, a reactor coolant leak of 1.4 Mg/hr developed in the fuelling vault. Operators determined that the east fuelling bridge had dropped 40 cm. The reactor was shutdown and cooled. Coolant pressure was maintained by transfer from other units and recovery from sump. Total leakage was 22 Mg ( approx. 10% of inventory). No safety system operation was required with the exception of containment box-up on high activity after one hour. There was no abnormal release of radioactivity to the environment.
BASIS FOR RATING: Defence-in-depth degradation. 0/1 real, expected - 1.4 Mg coolant leak, -full safety system availability, - short time scale, no difficulty. +1 -design anomaly (F/M Interlocks) not discovered by Surveillance Programme,-could have been worse if channel plugs had been removed.
DIFFICULTIES IN RATING:

Location: BRUCE-4
Event date: Tue, 23-01-1990
Nuclear event report
Legenda & explanation