Effect of Irradiation on Terminal Solid Solubility of Hydrogen in Zr-2.5Nb

Knowledge of the temperature dependence of hydrogen solubility is used to define the conditions necessary for brittle hydrides to be present in reactor components during service. The terminal solid solubility (TSS) of hydrogen is affected by several factors, including irradiation, cold work, and decomposition of the beta phase in Zr-2.5Nb. TSS temperatures for specimens irradiated in Osiris, Halden, and CANDU (R) reactors are reported. TSS was measured on Zr-2.5Nb specimens using differential scanning calorimetry (DSC) to complete four heat-up/cool-down cycles (heat to a peak temperature and cool to room temperature at a rate of 10 degrees C/min) followed by a 1-h anneal at 500 degrees C, and then four more heat-up/cool-down cycles. As with Zircaloy, irradiation slightly decreases the TSS temperatures, but subsequent annealing increases them. These changes are attributed to an initial effect of irradiation damage and reconstitution of the beta phase and reversal of these effects by annealing, as indicated by X-ray diffraction data showing reduced dislocation density and higher beta-phase volume fraction after the specimens were annealed.