PNNL

Abstract

Solution annealed(SA) 304 and cold-worked(CW) 316 austenitic stainless steels were irradiated with protons in order to study the potential effects of helium, irradiation dose, and irradiaiton temperature on microstructural evolution, especially void swelling, with relevance to the behavior of austenitic core internals in Pressurized Water Reactors(PWRs). These steels were irradiated at 300C with 1 MeV protons at doses up to 10 dpa. Both steels were irradiated either with or without 15 appm helium pre-implanttion. Irradiation was also conducted at 340C, but only with 15 appm helium pre-implantation. Transmission electron microscopy (TEM) revealed that small, heterogeneously distributed voids were observed in both alloys at 300C, but only after helium pre-implantaion. At 340C, however, both SA 304 and CW 316 steels exhibited homogenous void formation, suggesting a significant role of both helium and irradiation temperature in void nucleation. Compared with CW 316 voids developed sooner in the SWA 304 alloy at 300 and 340C, consistent with the behavior observed at higher temperature (>370C) in the EBR-II fast reactor, but the development of the Frank loop microstructure with increasing exposure with similar in both alloys. Helium pre-implantation had a measurable effect on the details of Frank loop formation.