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.
Event date: Mon, 06-07-1992