Mechanical behavior at high temperature of highly oxygen- or hydrogen-enriched α and (prior-) $\beta$ phases of zirconium alloys

Abstract : During a hypothetical loss-of-coolant accident (LOCA), zirconium alloy fuel claddings can be loaded by internal pressure and exposed to steam at high temperature (HT, potentially up to 1200°C) until they are cooled and water quenched. A significant fraction of the oxygen reacting with the cladding during oxidation at HT diffuses beneath the oxide through the metallic substrate. This diffusion of oxygen induces a progressive transformation of the metallic $\beta _{Zr}$ phase layer into an intermediate layer of $\alpha _{Zr}$(O) phase containing up to 7 wt.% of oxygen. Furthermore, in some specific conditions, the cladding may rapidly absorb a significant amount of hydrogen during steam exposition at high temperature. Then, hydrogen, as a $\beta _{Zr}$-stabilizer, would mainly diffuse and concentrate up to several thousands of wt.ppm into the inner$\beta _{Zr}$ phase layer