FAILURE OF TWO DIESEL GENERATORS WHILE ROUTINE TESTING DURING UNIT MAINTENANCE
Monday, October 5, 1992
Restart operations were in progress at the unit with reactor at the minimum controlled power level. While testing safety system (SS) train 2 under the load sequencing program DG-2 failed to start. While testing SS train 1 under the above program DG-1 failed to start as well. In accordance, with the procedure the reactor was brought to subcriticality. Defect in SS train 1 was corrected (speed controller maladjustment at DG-1) and DG-1 was placed in expectation (hot standby) mode. After defect elimination (failure of 6 kV breaker's electric drive) and successful testing DG-2 was placed in hot standby. Breach of unit safe operation condition occurred due to failure of two trains of emergency power supply system. Basis for event rating: No real initiator. Failed safety system equipment is intended for expected initiator. Safety function availability - adequate. According to Table A1 - Level 1/2 (C-1P). Level 1 was chosen.