Terminal Solid Solubility of Hydrogen in Hafnium

The terminal solid solubility (TSS) of hydrogen during hydride dissolution/precipitation is determined by differential scanning calorimetry technique for nonirradiated hafnium (Hf) that is used as control rods of light water reactors. The hydrogen concentration in hydrogenated Hf samples ranged from 27 to 300 wt ppm. The reliability of the TSS data obtained for Hf was confirmed using those for Zircaloy-2 (Zry-2) obtained in this study with the literature data, and best-fit equations for the obtained TSS curves for Hf are derived. The TSS for Hf at 573 K, which corresponds to an operational temperature of control rods in boiling water reactors, is in the range of 10–15 wt ppm, and is found to be 1/5–1/7 of the TSS for Zry-2.