The primary function of valves is to control the flow of fluids. Valve functions include the following:
1. Starting and stopping flow
2. Regulating flow-throttling
3. Preventing reverse flow-checking reverse flow
4. Changing flow direction
5. Limiting pressure-pressure relief
Valves are selected to perform these functions in fluid systems for nuclear power plants. The valves control the flow through these nuclear plant fluid systems and thus the operation of the systems. Nuclear plant fluid systems have varying degrees of importance depending on their function. The reactor cooling system is critical to maintaining the temperature of the fuel charge and transferring energy to the steam generator. The steam system transfers energy from the steam generator to the turbine and then to the condenser. In addition to these primary fluid systems there are many others that provide for operation of the plant. Some of these systems are related to the safe operation of the power plant. Others are not safety related and therefore are not covered by the requirements of the Code. This commentary will explain how the ASME Boiler and Pressure Vessel Code (BPVC) requirements are implemented for safety-related nuclear valves.