Functional tests of French safety valves, type SEBIM, for their fitness for use in the primary system of German pressurized water reactors

Abstract

Several safety requirements are made to the operativeness of the relief and safety valves of the pressurizer of German pressurized water reactors. Reliable pressure limitation and - if necessary - reduction to the required pressure must be warranted by them under any transient plant conditions, in case of operational transients and accidents. In addition, the valves must reliably close again if there are requirements for opening and in the event of malfunction in order to avoid loss of coolant accidents. These different requirements result in the fact that the valves must be able to discharge different media such as hydrogen, steam and water. To enable the valves of the pressurizer to meet all specific requirements made to them, retrofittings and modifications to a different extent are required for German pressurized water reactors. In doing so it must be warranted that the valves used will neither show any instable behaviour due to the different discharge media nor cause any relevant strain produced by pressure waves on the adjacent conduits. For retrofitting of the safety valves of the pressurizer, the French company SEBIM, too, proposes a concept for the protection of the primary circuit against exceeding pressure. To prove the functional reliability of safety valves, type SEBIM, under the thermohydraulic conditions prevailing in German pressurized water reactors, an extensive test programme was carried out on the CUMULUS test facility (true scale [1:1] of the real plant) of Eléctricité de France. Due to the positive results obtained in these tests it is to be stated that the safety valves, type SEBIM, stand for an interesting solution for the protection devices of the primary system of German pressurized water reactors (DWR) against exceeding pressure.