EPR – Areva brochure

■ EPR NUCLEAR ISLANDPRESSURIZER†CHARACTERISTICSDATAPressurizerDesign pressure176 barDesign temperature 362 °CTotal volume 75 m 3Total length14.4 mBase material18 MND 5 (low alloy ferritic steel)Cylindrical shell thickness140 mmNumber of heaters 108Total weight, empty150 tTotal weight, filled with water225 tNumber and capacity of safety valve trains 3 x 300 t/hDepressurization valves capacity900 t/hComputer-generated image of the EPR pressurizer head with its safety and relief valves.The pressurizer (PZR) role is to maintain the pressure of theprimary circuit inside prescribed limits. It is a part of the primarycircuit, and is connected through a surge line to the hot leg ofone of the four loops of that circuit.The pressurizer is a vessel containing primary water in its lower part,and steam water in its upper part. To accommodate some primarycoolant volume variation, the pressurizer is equipped with electricheaters at its bottom to vaporize more liquid water, and with a spraysystem at its top to condense more steam. Compared to previousdesigns, the volume of the EPR pressurizer has been significantlyincreased in order to smooth the response to operationaltransients. This improvement provides a gain in terms of equipmentlife duration and a gain in terms of time available to counteractpotential abnormal situations in operation.Relief and safety valves at the top of the pressurizer protect theprimary circuit against overpressure. Compared to previous designs,the EPR features an additional set of motorized valves; in case ofpostulated accident with a risk of core melting, these valves wouldprovide the operator with an additional efficient mean to rapidlydepressurize the primary circuit and avoid a high pressure core meltsituation.A number of construction provisions have improved maintainability.In particular, a floor between the pressurizer head and the valveseases heater replacement and reduces radiological dose duringvalve service.All the pressurizer boundary parts, with the exception of the heaterpenetrations, are made of forged ferritic steel with two layers ofcladding. The steel grade is the same as that for the reactor pressurevessel. The heater penetrations are made of stainless steel andwelded with Inconel.Pressurizer erection in a reactor building.The pressurizer is supported by a set of brackets welded to the mainbody. Lateral restraints would preclude rocking in the event of apostulated earthquake or accident.† The pressurizer has a larger volumeto smooth the operating transientsin order to:• ensure the equipment 60-year design life,• increase the time available to counteractan abnormal operating situation.† Maintenance and repair (concerningsafety valves, heaters) are facilitatedand radiological doses are reduced.† A dedicated set of valves for depressurizingthe primary circuit is installed on thepressurizer, in addition to the usual reliefand safety valves, to prevent the risk ofhigh pressure core melt accident.32 II 33