Radiation-induced segregation in heavy ion irradiated stainless steels. 1. Grain boundaries analysis by FE-TEM and an application of the segregation prediction code

Radiation-induced segregation (RIS) which occurs near grain boundaries (GBs) in alloys has been considered as one of the major factors of the life degradation which occurs in the reactor internals of nuclear reactors. It is important for the elucidation of RIS mechanism. In this study, grain boundaries (GBs) analysis using by transmission electron microscope equipped with field emission gun (FE-TEM) are conducted for heavy ion irradiated solution-annealed and thermally sensitized 304 stainless steels (SSs) at various conditions. The applicability of RIS prediction code which was developed by CRIEPI is investigated by comparing with the measured data. Main results are as follows: (1) In solution-annealed SS, chromium enrichment, iron and nickel depletion at GB before irradiation were observed, while chromium depletion, nickel and silicon enrichment at GB were detected after irradiation. (2) In thermally sensitized SS, chromium concentration at GB after irradiation decreased, and nickel and silicon enrichment were observed in comparison with unirradiated condition. (3) In both solution-annealed SS and thermally sensitized SS, the calculated chromium concentration profile near GB indicated good agreement with measured data, but the calculation for iron and nickel is not good. It was found that the optimization of physical parameter for the prediction code was required in order to improve the precision of the prediction code. (author)