Baseline Properties and DBTT of High-Burnup PWR Cladding Alloys

Pre-storage drying-transfer operations and early stage storage can subject cladding to high enough temperatures and hoop stresses to induce radial hydride precipitation during long-term dry-cask cooling. These radial hydrides would provide an additional embrittlement mechanism in response to hoop-stress loading during post-storage fuel retrieval and cask transport. Argonne has developed a test protocol for studying high-burnup cladding embrittlement: (1) radial-hydride treatment, during which high-burnup cladding is exposed to simulated drying-storage temperature and stress histories, including slow cooling, and (2) ring compression tests (RCTs), which induce hoop bending stresses in cladding rings that allow determination of strength and ductility as functions of RCT temperature, as well as the ductile-to-brittle transition temperature (DBTT). The protocol was used to generate DBTT data for high-burnup Zircaloy-4 (Zry-4) and ZIRLO™ for the U.S. Nuclear Regulatory Commission and high-burnup M5® for the U.S. Department of Energy (DOE). Under DOE sponsorship, Argonne has also generated baseline properties for the characterization of as-irradiated Zry-4, ZIRLO™, and M5® as well as their RCT strength and ductility. The baseline properties are presented along with a comparison between the strength and ductility of irradiated high-burnup cladding before and after exposure to simulated drying-storage temperature and stress histories.