Study of effect of carbon on irradiation-induced grain-boundary phosphorous segregation in reactor pressure vessel using first-principles-based rate theory model

Ebihara, Kenichi   ; Yamaguchi, Masatake   ; Nishiyama, Yutaka ; Onizawa, Kunio ; Matsuzawa, Hiroshi*

The experimental results on neutron-irradiated reactor pressure vessel (RPV) steels have revealed grain boundary (GB) segregation of phosphorous(P) causing GB embrittlement. Since the dependence of the segregation on dose and dose-rate is unclear due to the lack of experimental database, the estimation of the irradiation-induced GB P segregation by the rate theory model is desired. In this presentation, we incorporated the effect of carbon(C) into the model by considering C as the trap of vacancies(Vs) and self-interstitial atoms (SIAs), and evaluated the GB P coverage in the RPV steels. As a result, by selecting the proper sink strength of V and SIA, the simulation reproduced the experimental GB P coverage. It was confirmed that C hardly influences the dose rate dependency of the GB P coverage. It was found that C influences the GB P coverage by mainly slowing the V migration. Therefore it is considered that V is necessary for simulating GB P coverage even though V hardly transports P.