RISK ANALYSIS OF SURVEILLANCE REQUIREMENTS INCLUDING THEIR ADVERSE-EFFECTS

Technical specifications for nuclear power plants require periodic surveillance testing of the standby systems important to safety. This regulatory requirement is imposed to assure that the systems will start and perform their intended functions in the event of plant abnormality. However, operating experience suggests that, in addition to the beneficial effects of detecting latent faults, the tests may have adverse effects on the plant's operation or equipment. This paper defines those adverse effects of testing from a risk perspective, and then presents a method to quantify their associated risk impact, focusing on plant transients and the wear-out of safety systems. The method, based on probabilistic safety assessment, is demonstrated by applying it to several surveillance tests conducted at boiling water reactors. The insights from this evaluation can be used to determine risk-effective intervals for surveillance tests.