Contribution to the study of the pseudobinary Zr1Nb–Oxygen phase diagram by local oxygen measurements of Zr1Nb fuel cladding after high temperature oxidation

This work is concerned with measurement of oxygen concentrations and construction of the pseudobinary Zr1Nb–O phase diagram, acceptable for diffusion models predicting the oxidation behavior of Zr1Nb fuel cladding during thermal transients such as LOCA. Oxygen concentrations were measured in existing phases in the wall of Zr1Nb nuclear fuel cladding tubes after the high-temperature oxidation. The oxygen concentrations at the α/α + β phase boundary in the α-Zr(O) layer have been determined using WDS method. Oxygen concentrations in the prior β-Zr were measured using two experimental methods (SIMS and TEA). Consequently, the ceiling of the oxygen concentration in β-Zr has been assessed based on the results of SIMS, TEA, and microhardness measurements. Eventually, the experimental results were compared to the pseudobinary Zr1Nb–O phase diagram, calculated using CALPHAD software, with satisfactory agreement. The effect of hydrogen was also examined.

► Oxygen concentrations inside oxidized fuel claddings were measured.
► A part of pseudobinary Zr1Nb–O phase diagram has been constructed.
► The phase diagram can be constructed up to a few units of wt.% of O.
► The hydrogen effect on the oxygen concentration was assessed.