Preliminary Analysis of Candidate Alloys for Use in the CANDU-SCWR

Abstract

The newly commissioned test loop at the University of New Brunswick was used to test two ferritic steels as potential candidates for use in the CANDU-SCWR. The first steel comprised of 14%-Cr was selected as the base metal for processing into an oxide dispersion strengthened (ODS) steel. Due to its good corrosion resistance but relatively low ductility, the second steel with 25%-Cr has been considered as a coating material. Coupons cut from both alloys were exposed to supercritical water in the as-cast, as-rolled, and rolled plus homogenized conditions. Corrosion experiments took place at 500 degrees C and 25 MPa for durations of 100, 250 and 500 hours. The purpose of this study was to examine the corrosion rate and oxide formation characteristics for these two steels. Preliminary weight change results indicate weight gain increasing with exposure time for the 14%-Cr steel. This correlates with the growth of a continuous dual layer oxide as seen in cross-sectional SEM work. The inner layer consists of a chromium-rich, iron-depleted oxide, while the outer layer is an iron-rich oxide deposited on the surface. For the 25%-Cr coupons, the weight change was very small, in agreement with the SEM work that showed very little oxide growth.