The capability of nuclear electricity generation by French Utility’s EDF (Electricite´ de France) is 75% of global generation, 58 PWR units are in operation, 34 units three-loop, 20 units four-loop (1300MWe) and 4 units four-loop (1450MWe). The French Utility methodology to justified reactor vessel assessment on specific plants is to verify, for a known defect (real or hypothetic), safety margin to non ductile failure for each transient and for case of loading. The demonstration must be done for each instant of the reactor vessel life, and must include material embrittlement caused by irradiation degradation. This paper will describe EDF methodology aging assessment for at least 40 years, comparing: • The boundary RTNDT (Reference Nil Ductility Transition Temperature) support by reactor vessel. • The estimated RTNDT at 40 years. Estimated RTNDT for 40 years is determined with a prediction formula that needs following input parameters: • The initial RTNDT during the construction. • Fluence assessment received by reactor vessel during 40 years in operation. • Chemistry material composition. The Boundary RTNDT supported by reactor vessel is determined with a mechanical analysis that needs the following input parameters: • Defect characteristics. • Transient definition. The determination of each parameter will be described, and an experimental program to verify the conservatism of methodology will be presented (Irradiation Surveillance Programme).

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