Calculating margin for valve operation under design basis conditions requires evaluation of the stem loads required to operate the valve and the load capability of the actuator. These evaluations require justified and validated methodologies with verified inputs to implement the methodologies. The lack of validated methodologies in the past led to plant events and issues that prompted three NRC generic letters for MOVs and numerous generic correspondence documents from the NRC on AOV and MOV

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... formance. Over the past 25 years, EPRI has performed extensive research to better understand the performance of valves and power operators. This research has been used to develop predictive methods for the evaluation of valve required operating loads and actuator output capability. This paper summarizes EPRI's research related to the development of predictive methodologies for valves and power operators and methods that are available, specifically methods for: • Predicting required operating loads under design basis conditions, • Predicting actuator output capability, • Addressing thermal binding of gate valves, and • Addressing the rate-of-loading phenomenon for MOVs. This paper also describes a recent project to develop and validate a method for predicting the required thrust to overcome friction between the valve disk and body due to disk sideloading in cage-guided balanced disk globe valves.