This paper presents issues associated with Chilled water system operations at a Nuclear facility that experiences problems with the cooling water flow control valves during the cold season under low load conditions. The system is used to provide safety related functions of cooling rooms such as the control rooms due to radioactive and toxic gas hazards. The valves experience excessive cycling under low load conditions during the cold seasons leading to maintenance and availability problems with the system. This problem is driven by the current system design and the need to utilize a chilled water system during times when natural ambient temperature conditions are low. The Chilled water system uses refrigeration units to cool the chilled water and service water to provide the heat sink for the refrigeration condensing units. The focus of the discussion is the cooling water (service water) flow control valves, which are the major source of the maintenance problem. The paper presents the integrated behavior of the Chilled water system to properly characterize the issue and the solutions. The paper will present the system details and performance parameters necessary to evaluate the problem. The behavior of the valves will be evaluated based on the system operations. This paper evaluates the technical merits of several options to provide stable control of the flow control valves, prevent high-pressure chiller unit trips and solve flow control valve actuator excessive wear.

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