Ensuring MOV reliability through material qualification and testing

Safety systems in nuclear plants must have a high degree of assurance of operability when called upon. In turn, the individual safety system components must have a high degree of reliability. Motor Operated Valves (MOV5) are of particular concern. To ensure reliable operation over the entire operating life of the plant, these major components require sound material qualification and test support data. Over the past 10 years, Atomic Energy of Canada Limited (AECL) has worked in partnership with the station design and maintenance support groups to address generic MOV material qualification issues. Recent technological advancements have helped to ensure reliable MOV operation. These include diagnostic equipment, improved lubrication, better elastomers, proven packing materials and configurations, validated coefficient of friction (COF) data for hardfacing materials and computer software to perform thrust and torque calculations. The knowledge gained has resulted in significant improvements to the design specifications used to purchase new valves and spare parts. This paper highlights the work on coefficient of friction (COF) for nickel-based hardfacing alloys, the improvements in valve stem packing and the valve stem nut lubrication studies. These research and development (R and D) efforts illustrate the importance of working with station maintenance and engineering staff to address all critical MOV components. Application of the knowledge gained in support of improving CANDU station reliability is discussed. (author)