STUDY ON PROMOTING USE OF REPAIR, REPLACEMENT AND MITIGATION TECHNIQUES IN MAINTENANCE ACTIVITIES OF NUCLEAR POWER PLANTS

摘要

Maintenance of nuclear power plant facilities involves activities comprising a large system composed of both plant hardware and human subsystems to assure safe and reliable operation. Maintenance activities are composed of inspection, evaluation and corrective measures. Corrective measures are countermeasures for aging degradation, e.g., resetting the inspection period based on the results of inspection and evaluation; mitigation of degradation phenomenon; repair or replacement; preventive maintenance; etc. The corrective measures merit special attention as they are important and valuable actions in order to promote continued efficient and safe plant operations. It is necessary to develop a set of regulatory and industrial technical requirements for a well-structured, documented set of standards, so that corrective measures can be used and applied uniformly and effectively. Currently the code and standard system is less developed in Japan than in the United States. In this study, the authors considered the relationship between degradation and maintenance and the difference of performance requirements between the plant construction stage and the in-service stage. This effort is intended to clarify the issues of regulation for maintenance activities, with an objective to help develop structured regulatory/industrial requirements with a code and standards consistent with appropriate corrective measures. The Nuclear Regulation Authority (NRA), the regulatory body in Japan, has reviewed the present Japanese inspection system in response to suggestions from the Integrated Regulatory Review Service (IRRS) mission established by International Atomic Energy Agency (IAEA). The NRA has also been developing a new regulatory inspection system similar to the Reactor Oversight Process (ROP) used in the United States. The expectation for the new Japanese inspection system is to focus regulations on plant issues with higher risk importance, considering both plant hardware and human subsystems. The new Japanese regulatory system addressing maintenance is also expected to enhance electric utilities ability to assure safely is self-motivated and sustained.