| Abstract | One of the major challenges for the Canadian Gen IV Super-Critical Water-cooled reactor (SCWR) concept is the selection of fuel cladding materials. The Canadian SCWR concept will operate at a core outlet temperature of 625 oC and 25 MPa of pressure with peak cladding temperature reaching as high as 850 oC. Corrosion resistance is an important factor for materials selection. Austenitic stainless steels that contain Cr contents greater than 18 wt% are generally considered to provide adequate corrosion resistance. In this work, an austenitic stainless steel 310 containing 24 wt% Cr is assessed for corrosion resistance at 625 C for 1000 hours in superheated steam, in water at 8 MPa (subcritical) and at 25 MPa (supercritical). Results indicate that the material exposed to subcritical water has the thickest oxide, at 10 micrometer, while that exposed to supercritical water has a 1 micrometer thick oxide, and the oxide exposed to superheated steam was 0.2 micrometer thick. Transmission Electron Microscopy (TEM) revealed that 310 exposed to different pressure conditions at 625 oC. (i.e., superheated steam, subcritical and supercritical water conditions) had generally the same type of the oxide structure, i.e., a Cr rich spinel structure on the top surface. Cr-depleted recrystallized austenite grains were underneath the spinel structure. The adjacent large-grained austenite substrate had M23C6 carbides in the grain interior. The implications of these results are discussed. |
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