Combined effects of temperature and of high hydrogen and oxygen contents on the mechanical behavior of a zirconium alloy upon cooling from the βZr phase temperature range

Abstract During hypothetical loss-of-coolant accidents (LOCA), zirconium-based nuclear fuel claddings can be exposed to high temperatures in the βZr phase domain and absorb substantial amounts of hydrogen (up to about 3000 weight ppm) and oxygen (up to about 1 weight %). This paper provides novel data about the combined effects of high hydrogen and oxygen contents on the mechanical behavior of the (prior-)βZr phase, as a function of temperature, upon cooling from the βZr phase temperature range. A protocol was developed to homogeneously charge Zircaloy-4 cladding tubes at different hydrogen contents, up to 3200 weight ppm, and oxygen contents, between 0.13 and 0.9 wt%. Tensile tests were then performed at various temperatures between 700 °C and 30 °C upon cooling from the βZr domain. The results show that the mechanical behavior strongly depends on the testing temperature and the hydrogen and oxygen contents. Relationships are proposed to describe the macroscopic ductile-to-brittle transition and the mechanical behavior of the material as a function of temperature, hydrogen and oxygen contents. The predictions based on these relationships are compared to selected data from the literature obtained on claddings oxidized at high temperature, including results from semi-integral LOCA tests. Also, it is shown that considering the combined effects of hydrogen and oxygen is necessary to interpret the material's mechanical behavior, particularly the embrittlement of claddings subjected to LOCA-relevant secondary hydriding.