Surveillance test and monitoring strategy for the availability improvement of standby equipment using age-dependent model

• An age-dependent unavailability model for standby equipment was investigated.
• An Online Monitoring-based Inspection Method was suggested.
• Changing the test interval for each standby turn was suggested.
• The effectiveness of the suggested methods was analyzed quantitatively.

In many cases, the safety of a nuclear power plant greatly depends on the successful operation of specific standby equipment at the time of demand arrival. For the effective management of safety-critical standby equipment, unavailability measures are introduced and widely applied. In this study, we propose an age-dependent unavailability model for standby equipment that considers aging-relevant information, such as the number of actual operations, the elapsed time from installation, and maintenance activities, in an integrated manner. Based on the proposed model, we present two availability enhancement strategies: the Online Monitoring based Inspection Method (OMIM) and the Shortening Surveillance Test Interval Method (SSTIM). In the OMIM, ‘elapsed-time sensitive׳ elements are monitored, without actual operation, at the differentiated monitoring interval with the help of sensing devices. For the remaining parts of the elements, actual testing is performed with an adaptive interval for each standby turn by the SSTIM. The effectiveness of the proposed enhancement schemes is demonstrated through a case study for the motor-operated valve (MOV). It is our belief that the proposed schemes can be widely applied in areas such as equipment testing, maintenance strategies, dynamic probabilistic safety assessment (PSA), and risk-informed regulations.