ABSTRACT
The reactor was shut down at the time. There were neither casualties nor contamination. The incident had been reported under reportable incidents’ procedures and appropriate modifications made.
Fuelling machine
In November 1978, on-load refuelling at full power was suspended when one fuel assembly gave difficulty during its discharge from the reactor. Inspection of the fuel assembly during discharge using remote viewing equipment and with the reactor shutdown revealed that the graphite sleeves of three of the eight fuel elements which make up the fuel stringer had been severely damaged. Examination of the graphite sleeve debris recovered from the reactor indicated that one sleeve had been broken by the differential pressure which exists across the pressure dome and which is imposed upon the fuel assembly during initial loading. This damaged sleeve allowed a partial bypass of the coolant during its subsequent irradiation and probably caused overheating of the lower fuel elements which eventually led to premature fuel pin failure. The fission product gas leakage into the coolant was detected by the gas activity monitoring equipment and action was taken to discharge the fuel assembly which led to this incident.
