Characteristics of the New Embrittlement Correlation Method for the Japanese Reactor Pressure Vessel Steels

Neutron irradiation embrittlement of reactor pressure vessel steels is an important aging issue for the long-term operation of light water reactors. A new embrittlement correlation method was developed by Central Research Institute of Electric Power Industry and the Japanese electric utilities in 2007. This method is primarily based on the fundamental understandings on the embrittlement mechanisms, i.e., microstructural changes were modeled by the mathematical form of rate equations, and the predicted microstructural changes were further correlated with the mechanical property changes in transition temperature region. The coefficients of the rate equations were optimized using the Japanese surveillance data of RPV embrittlement. This method was adopted as the revision of the Japanese code, JEAC4201-2007, in 2007. In this paper, after a brief explanation on the new correlation method, the predictions of the new method will be investigated through comparisons with the previous correlation, JEAC4201-2004, and the U.S. surveillance data in order to identify the characteristics of the new method.