Overpressure discharge lines

Each cylinder discharge line should have a relief valve located upstream of the cooler. Like all reciprocating devices, the piston will continue to increase pressure if flow is blocked. The relief valve assures that nothing is overpressured. It must be located upstream of the coolers as icc can form in the coolers, blocking flow. 

On French plants, cold overpressure protection is provided by pilot operated safety valves on the pressurizer when the RHR system is isolated. When the RHR system is operating, the protection is provided by pilot operated safety valves on the discharge lines from the RHR pumps. All these valves are qualified to operate in water conditions. In addition, specific requirements have been included in the Technical Specifications. 

For the Rovno NPP Unit 4, two new safety valves are to be installed which are provided by the Russian manufacturer according to the national standards to protect against cold overpressure. The actuation pressure is 20 bars since the design pressure of the discharge line of the RHR system is 22 bars. 

Overpressure relief systems, including safety and/or relief valves, valve discharge lines and any associated equipment ... 

A pressure relief function is used to control large pressure transients. This system will operate safety/relief valves following closure of the main steam isolation valves or the sudden closure of the turbine admission or stop valves and failure of the turbine bypass system to relieve the excess pressure. For this fimction, the safety/relief valves discharge steam from the steam lines inside the drywell to the suppression chamber. Each safety/ relief valve is operated from its own overpressure signal for the relief fimction, and by direct spring action for the safety function. 

L-35 malfunctions open or bypass open on line 53 from discharge of relief caustic pumps Tubing compression fittings become loose or tubing and fittings are overpressured from a relief into caustic relief/ drain header... 

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