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Ha, Yoosung; Shimodaira, Masaki; Katsuyama, Jinya
no journal, ,
In Japanese surveillance program for RPV, the specimens are taken from base metal of a quarter thickness in a plate, weld metal and heat affected zone (HAZ) as representative materials. JEAC4201 specifies Embrittlement Trend Curve (ETC) for base metal but not for HAZ, because the fracture toughness of HAZ is considered to be generally better than that of base metal. However, since the microstructures in HAZ are inhomogeneous due to multi-pass welding, it is necessary to investigate the fracture toughness of HAZ with more specific basis. The Charpy impact properties and fracture toughness (T
and T
) derived from three representative positions in HAZ were compared with those of base metal. T and T of HAZ were lower than those of base metal, meanwhile the results of Charpy impact test and fracture toughness test for HAZ indicated a relatively large scatter.
Takamizawa, Hisashi; Nishiyama, Yutaka
no journal, ,
Irradiation embrittlement of reactor pressure vessel steels is usually predicted based on ductile-to-brittle transition temperature shift obtained by Charpy impact tests for unirradiated and irradiated specimens. It is important to understand the uncertainty in the evaluation by Charpy impact test when giving margins for structural integrity assessment using embrittlement trend curves and when discussing the need for surveillance specimens obtained from the weld heat affected zone. In this study, we modeled the temperature dependence of Charpy absorbed energy based on about 1900 datasets of unirradiated and irradiated Japanese and U.S. materials. Then we used Bayesian statistics to construct an evaluation model that could take into account the variation in absorbed energy, the number of tests, and test temperatures for each dataset. In my presentation, we will discuss the results of analyses for the effects of irradiation, difference between Japanese and U.S. materials, and product form on the uncertainty of the Charpy ductile-to-brittle transition temperature.