EPR – Areva brochure

SAFETY> NUCLEAR SAFETY page 45THREE PROTECTIVE BARRIERS page 45DEFENSE IN DEPTH page 46NUCLEAR SAFETYThe fission of atomic nuclei, performed in reactors to generate heat, brings into play largequantities of radiation-emitting radioactive substances from which people and the environmentmust be protected.This explains the need for nuclear safety, which consists of the set of technicaland organizational provisions taken at each stage in the design, construction and operationof a nuclear plant to ensure normal service, prevent the risks of an accident and limit itsconsequences in the unlikely event of its occurrence.> EPR SAFETY page 47Golfech 2, France (1,300 MWe):reactor pressure vessel and internals.DESIGN CHOICES FOR REDUCINGTHE PROBABILITY OF ACCIDENTS LIABLETO CAUSE CORE MELT page 47DESIGN CHOICES FOR LIMITING THECONSEQUENCES OF A SEVERE ACCIDENT page 50Nuclear reactor safety requires that three functions should befulfilled at all times:• control of the chain reaction, and therefore of the power generated,• cooling of the fuel, including after the chain reaction has stopped,to remove residual heat,• containment of radioactive products.It relies upon two main principles:• the three protective barriers,• defense in depth.The three protective barriersTHREE PROTECTIVE BARRIERSThe concept of the “three protective barriers” involves placing,between the radioactive products and the environment, a seriesof strong, leak-tight physical barriers to contain radioactivity in allcircumstances:• first barrier: the fuel, inside which most of the radioactive productsare already trapped, is enclosed within a metal cladding,• second barrier: the reactor coolant system is housed within a metalenclosure which includes the reactor vessel containing the coreconstituted by the fuel within its cladding,• third barrier: the reactor coolant system is also enclosed within ahigh-thickness concrete construction (for the EPR, this constructionis a double shell resting upon a thick basemat, whose inner wall iscovered with a leak-tight metal liner).† The resistance and leaktightness of just one of these barriersis sufficient to contain the radioactive products.SteamgeneratorPressurizerReactorcoolantpumpControlrod drivemechanisms321FuelassemblyReactorpressurevessel1 Fuel cladding2 Reactor coolant boundary3 Reactor containment44 II 45