The Reactor Pressure Vessel (RPV) is an essential component liable to limit the lifetime duration of pressurized water reactor (PWR) plants. The assessment of defects in RPV subjected to PTS (pressurized thermal shock) transients made at an European level does not necessarily take into account the beneficial effect of load history (warm pre-stress WPS) on the resistance of RPV material regarding the risk of brittle failure. Numerous experimental, analytical and numerical results are available, which confirm the beneficial effect of warm pre-stress on RPV steels, with an effective increase of the material resistance regarding the risk of brittle failure.

NESC VII (Network for Evaluating Steel Components), a new project dealing with WPS, has been launched in 2008 (in link with the European Network of Excellence NULIFE) with the participation of international organizations (involving R&D and Technical support, Utilities, Manufacturers, Safety & Regularory organizations). Based on experimental, analytical and numerical tasks, the project is focussed on topics generally non covered by past experience on WPS : biaxiality of loading on small and large-scale specimens, influence and effect of irradiation, applicability to intergranular fracture, modeling (including analytical and numerical models) … Among these tasks, new original WPS experiments are conducted on small, medium and large scale specimens to study the influence of biaxial loading on WPS effect, using a fully representative RPV steel (18MND5 steel similar to A533B steel).

A full description of NESC VII project, including the present status, is presented in this paper.

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