NESC VII Synthesis: A European Project for Application of WPS in RPV Assessment Including Biaxial Loading

Abstract

The Reactor Pressure Vessel (RPV) is an essential component liable to limit the lifetime of PWR plants. The assessment of defects in RPV subjected to pressurized thermal shock (PTS) transients made at a European level does not necessarily take into account the effect of load history (warm pre-stress WPS) on the resistance of RPV material regarding to 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 and significant increase of the material resistance regarding to the risk of brittle failure. NESC VII, a new project dealing with WPS, launched in 2008 with the participation of numerous international organizations (involving R&D, Utilities and Manufacturers, Technical supports, Regulatory), is now finished. Based on experimental, analytical and numerical tasks, the project focused on topics generally not covered by past experience on WPS: biaxiality of loading on small and large-scale specimens, effect of irradiation, modeling (including analytical and numerical models) … Among these tasks, new original WPS experiments have been conducted on small and large scale specimens to study the influence of biaxial loading on WPS effect, using a fully representative RPV steel. All WPS experiments have been interpreted with a wide panel of methods, including analytical, engineering and numerical analyses. A description of NESC VII project is presented in this paper including a synthesis of the available experimental, analytical and numerical results.