Development of NRC requirements for standby diesel generators based on recent operating experience

NRC's regulatory requirements pertaining to emergency diesel generators will continue to evolve. The need for enhanced maintenance and surveillance programs has clearly been identified. The reliance upon qualification testing and periodic surveillance testing has been retained but the test frequencies and conditions have been reduced to minimize the potential for creating new problems. An analysis of the requirements imposed by the Japanese and the resulting reliability levels achieved by them indicates that the NRC requirements appear to be headed in the right direction. The Japanese require EDGs to be routinely tested every two (2) weeks but do not require these to be fast/cold starts. A fast start is only performed at each refueling onstage. Between refuelings they do not change the frequency of surveillance tests based on the number of past failures and they do not require additional special tests when either an EDG or an offsite power circuit is lost. In addition, each EDG is completely overhauled and inspected every two (2) years. These requirements have resulted in almost failure free diesel operation at their nuclear plants