An application of PSA techniques to on-line maintenance program. A feasibility study of maintenance strategy during plant operation using PSA techniques

This study confirms an on-line maintenance possibility for a Japanese NPP from a plant risk management point of view. One-line maintenance has already been planned and executed in some NPPs in the United States. The problem preceding on-line maintenance is how to keep a certain level of plant safety with out of service condition, safety-related systems and components, during maintenance. Deterministically, the technical specification defines unplanned maintenance periods of safety related standby systems. Probabilistically, this principle is able to be verified by utilizing PSA technology. In this study a PSA method for Japanese PWR plants is applied to improve plant availability, and to investigate safety issues associated with on-line maintenance strategy, system configuration, management and financial advantage regarding Japanese plant constraints. On-line maintenance is one of the risk management activities to improve safety and manpower workload during shutdown. As a result of this study, core damage frequency can show that on-line maintenance of some safety related systems is able to be performed and that of other safety related systems, not. On-line maintenance for Japanese NPPs utilizing risk method, will be introducing maintenance programs during power operation, like as performed in the United States. It will be important to prepare guidelines for on-line maintenance principles for further risk management programs. (author)