French nuclear plant life management program reactor pressure vessel integrity assessment

The process used by French utility, concerning the Reactor Pressure Vessel assessment, applied on 58 PWR NPPs 3 loops and 4 loops Reactor, involves the verification of the integrity of the component by finite element mechanical studies, in all conditions of loading in relation with RTNDT (Reference Nil Ductility Transition Temperature), and considering all of parameters. This approach, is based on mechanical safety studies, to demonstrate the absence of risk of failure by brittle fracture. For these mechanical studies two major input data are necessary: 1. the fluence distribution and the Fluence values and RTNDT during the lifetime in operation for each NPPs, 2. the thermal-hydraulic and mechanical evaluation and temperature distribution values in the downcomer. The main results must show significant margins The major tasks and expertise engaged by EDF were: - more precise assessment of the fluence and neutronic calculations; - better knowledge of the vessel material properties, including the effect of radiation; - the NDE inspection program based on the inspection of the vessel wall, with a special NDE tool to inspect the area in subcladding zone. (author)