Shutdown risk impact assessment for extended containment leakage testing intervals utilizing ORAM{trademark}. Final report

This report documents a study of the shutdown risk implications of the implementation of proposed Option B to 10 CFR Appendix J using EPRI Outage Risk Assessment Management tool. The proposed revision would allow the extension of containment surveillance testing intervals based on the performance of this important fission product barrier. It was the objective of the study to take advantage of shutdown risk models developed in EPRI`s Outage Risk Assessment and Management software to evaluate a perceived shutdown risk benefit of increased surveillance test intervals. The methodology employed the review of initiating event data to determine if shutdown events related to ILRT/LLRT testing had occurred. A minimum of events (i.e., 7 in 436 shutdown events) were discovered. From this review and plant experience, a list of potential issues were identified for consideration. Engineering and operational experience from actual plants was used to revise the list of issues for consideration. The final quantification was reduced to two scenarios, one for the ILRT and one for the LLRT. The quantified risk benefit was on the order of 10{sup -7} per year of reduced shutdown related core damage frequency for both types of plant designs reviewed BWRs and PWRs. This supports amore » conclusion that there is a measurable risk benefit to the extension of the ILRT/LLRT test intervals specified for nuclear power plants. The estimated shutdown risk benefit was shown to be larger for BWRs, but given the uncertainties, this difference is judged to be insignificant. In conclusion, the original supposition that there is a shutdown risk benefit to the extension of containment surveillance test intervals has been supported by the evaluations documented in this study. The risk benefit, while not relatively large, is measurable. The insights documented in this report support an assertion that the reported risk benefit is also conservative and, depending on the plant, may be significantly lower.« less