Terminal solid solubility of hydrogen of optimized-Zirlo and its effects on hydride reorientation mechanisms under dry storage conditions

Abstract

TSSD, TSSP, and TSSP2 of hydrogen for optimized-Zirlo (Zirlo (TM)) alloy were measured by DSC in the range of 53-457 wppm. Solvus curves of the TSSs are derived and proposed in this study. The results show that the temperature gap between TSSD and TSSP solvus lines of Zirlo (TM) are similar to those of other zirconium alloys, but another gap between the TSSD and TSSP2 line differs significantly. In particular, the TSSP2 solvus line becomes closer to the TSSD solvus line than to TSSP unlike Zircaloy-4, so Delta TTSSD-TSSP2 of Zirlo (TM) decreases with decreasing temperature. This implies that hydride reorientation can take place more significantly in Zirlo (TM) than in Zircaloy-4, and the limited temperature variation of 65 degrees C during the vacuum drying and the cooling-down process may not be sufficient to prevent the triggering of hydride reorientation in Zirlo (TM) cladding under long-term dry storage.