Risk-based evaluation of AOT and STI requirements at ANO-1 nuclear power plant

Technical specifications of nuclear power plants contain the requirements for surveillance test intervals (STIs) of various standby components and establish the allowed outage time (AOT) for the on-line repair of components detected inoperable during testing. The objective is to assure that standby safety systems and components are available for accident mitigation conditions. Until now, these requirements have been determined primarily on the basis of engineering judgment; currently efforts are under way to develop a risk basis for AOT and STI modifications in nuclear power plants. In this paper, the risk impacts of various AOT and STI requirements are determined using probabilistic risk assessment (PRA) models. The methodology for evaluating the impacts of testing and maintenance activities is presented and its application to the Arkansas Nuclear One Unit 1 (ANO-1) power plant is demonstrated