Survey and evaluation of aging risk assessment methods and applications

The Nuclear Regulatory Commission (NRC) initiated the nuclear power plant aging research (NPAR) program about 6 years ago to gather information about nuclear power plant aging. Since then, this program has collected a significant amount of information, largely qualitative, on plant aging and its potential effects on plant safety. However, this body of knowledge has not yet been integrated into formalisms that can be used effectively and systematically to assess plant risk resulting from aging, although models for assessing the effect of increasing failure rates on core damage frequency have been proposed. The purpose of this review is to survey the work conducted to address the aging of systems, structures, and components (SSCs) of nuclear power plants (NPPs), as well as the associated data bases. The review takes a critical look at the need to revise probabilistic risk assessment (PRAs) so that they will include the contribution to risk from plant aging, the adequacy of existing methods for evaluating this contribution, and the adequacy of the data that have been used in these evaluation methods. A preliminary framework is identified for integrating the aging of SSCs into the PRA, including the identification of needed data for such an integration