A new approach to description of in-service embrittlement of WWER-1000 reactor pressure vessel materials

Based on available published data and experimental findings, the in-service embrittlement of materials has been analyzed. The contributions of thermal ageing and neutron irradiation to embrittlement of the base and weld metals of WWER-1000 reactor pressure vessels are discussed. Equations have been derived which describe the shift of the critical brittle temperature depending on the irradiation time and neutron fluence. For a nickel-rich weld metal a relation between the radiation embrittlement coefficient and the amount of alloying elements Ni, Mn, and Si has been defined.