Reliability assessment and maintenance planning of air-operated control valves used in a nuclear power plant

Air-operated valves (AOVs) are used to control and isolate different process systems in a nuclear power plant. The performance of an AOV is adversely affected by degradation in the pneumatic actuator and other control components of the valve. Therefore, valve overhauls (OH) are performed at a fixed interval that is mainly based on the vendor’s recommendations and the experience of the plant personnel. This paper presents a probabilistic approach to assess valve reliability and uses it as a basis to plan maintenance. The paper presents a Bayesian approach to model the valve lifetime distribution and update its parameters based on the in-service data available from the plant. Using this model, the valve OH interval is determined to achieve a target reliability level over the interval. A practical case study is presented that utilizes maintenance data from a fleet of 32-level control valves connected to steam generators at a Canadian nuclear power station. The proposed approach demonstrates that the satisfactory functioning of an in-service valve provides valuable information for extending its OH interval. Thus, the proposed approach can significantly improve the efficiency of the valve maintenance program.