Power pressure relief function

The safety/relief valves are dual-function valves discharging directly to the pressure suppression pool. The safety function provides protection against overpressure of the reactor primary system. The relief function provides power-actuated valve opening to depressurize the reactor primary system. The valves are sized to accommodate the most severe of the following two pressurization transient cases determined by analysis ... 

Valves. Valves control the way the gas is used, stopped, or directed. They must function under a variety and range of temperatures. Control or proportional valves in a process system are power-operated mechanisms able to alter fluid flow. A pneumatic valve actuator adjusts valve position by making the air pressure either linear or rotary motion. Ball valves provide the shutoff capability. Gas valves are specialized to control the flow of another medium, such as natural gas. A pressure relief valve is a self-actuated safety valve that relieves pressure. A butterfly valve controls the flow of air or a gas through a circular disk or vane by turning the valve s pivot axis at right angles to the directing flow in the pipe. 

Diversion of flow safely All the above systems discussed are part of electronic system requiring power. As a next layer of protection there are mechanical devices (requiring no power to meet power failure situations) to divert the flow safely. Safety and relief valves are used to in case to depressurize when SIS fails to take care (e.g., say due to control power failure). Pressure relief valve diverts the fluid for safe passage. These relief valves are spring force to close so that when pressure is below setting it is closed. Many cases rupture discs are used but in that case system needs to be closed to attain the disc. To a certain extent quartz bulb in sprinkler system does the same function. 

The function of the control system is to regulate the operation of the pump. The latter pumps fluid from an infinitely large reservoir into the tank. We shall assume that it takes 60 s to pressurize the tank. The pressure switch has contacts, which are closed when the tank is empty. When the threshold pressure has been reached, the pressure switch contacts open, de-energizing the coil of relay K2 so that relay K2 contacts open, ranoving power from the pump, causing the pump motor to cease operation. The tank is fitted with an outlet valve that drains the entire tank in an essentially negligible time the outlet valve, however, is not a pressure relief valve. When the tank is empty, the pressure switch contacts close, and the cycle is repeated. 

Selected safety/relief valves are associated with the automatic depressurization of the primary system under assumed LOCA conditions. These valves have two independent logic channels powered from different power sources, either of which can initiate depressurization. Valves open automatically and remain open imtil the pressiue falls to a preset closure pressure. These valves open automatically upon signals of high drywell pressure and low reactor water level and confirmation of one LPCI function of the RHR system or LPCS system running. Initiation signals need not be simultaneous. The valves remain open until the primary system pressure is reduced to a point where the LPCI function of the RHR system and/or the LPCS system can adequately cool the core. The initiation of automatic depressurization is delayed from 90 to 120 s to allow the operator to terminate the initiation should the HPCS system initiation and acceptable reactor vessel level have been confirmed. 

In the analysis of CR ejection at hot standby , the inserted reactivity is set as 2.8%dk/k. The peak fuel enthalpy is below 150 cal/g. The increase in the pressure is more extensive compared to the full power case. The active initiation of the SRVs (in their relief valve function) is not credited. The SRVs are assumed to open passively as the safety valve function. The peak pressure is 27.2 MPa. 

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