Effect of Nb addition on the terminal solid solubility of hydrogen for Zr and Zircaloy-4

The terminal solid solubility of hydrogen (TSS) for pure Zr, Zr–Nb binary alloys with different Nb concentrations, and Nb added Zircaloy-4 was examined from the view point of the integrity of new-type nuclear fuel cladding. These alloys were hydrogenated by a modified UHV Sieverts’ apparatus at 973 K. The hydrogen concentration and the hydride dissolution temperature of specimen were measured by using a hydrogen analyzer and a differential scanning calorimeter (DSC), respectively, and then the terminal solid solubility of hydrogen was determined. The TSS of the α single-phase Zr–0.3Nb (Zr–0.3 wt.% Nb) specimen appeared to be almost same as that of pure Zr. On the contrary, the TSS of the Zr–1.0Nb and Zr–2.5Nb alloys, which were α + β biphasic specimens, were larger than that of pure Zr and slightly increased with Nb concentration. The increment of TSS by Nb addition was slightly larger than that by the traditional additive elements of Sn, Ni, and Cr in Zircaloys. The Nb added Zircaloy-4 had higher TSS than the Zircaloy-2 and -4, which was attributed to the further additive effect by βZr precipitation in Zircaloy besides the traditional additive element effects.