Keywords: RPV steel, reactor pressure vessels, WWER reactors, chemical composition, copper, phosphorus, nickel, manganese, radiation embrittlement, nuclear power plants, NPP, nuclear energy, nuclear safety, safety assessment, matrix damage, irradiation-induced precipitation, element segregation
The role of chemical composition in WWER RPV irradiation embrittlement
The main chemical elements influencing WWER RPV steel radiation embrittlement are copper, phosphorus, nickel and manganese. Copper and phosphorus are the main influencing elements for WWER-440 RPVs. The influence of copper is implemented in the forming of nanocluster centres rounded by other elements which are the effective barriers to dislocation movements. Phosphorus segregates inside the grains, interacting with matrix defects and attracted to the Cu-type precipitates. Phosphorus also migrates to grain boundaries through diffusion processes. Due to the higher nickel content and very low copper and phosphorus present in WWER-1000 RPV steel, the main influencing element for this RPV type is nickel. The manganese content also has to be taken into account due to synergism of Ni and Mn. The semi-mechanistic model is based on key embrittlement mechanisms of chemical elements influence: matrix damage, irradiation-induced precipitation and element segregation proposed.