Uncertainty evaluation of Charpy ductile-to-brittle transition temperature using Bayesian inference

Takamizawa, Hisashi ; Nishiyama, Yutaka 

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.