Effect of pre-oxidation temperature on the ductility of a zirconium alloy cladding under simulated accident conditions

Abstract

The ductility of a zirconium alloy cladding tube pre-oxidized at 900, 1000, 1100, and 1200 °C was evaluated after subsequent oxidation at 1000 and 1100 °C by performing ring compression tests. For comparison, ring compression tests were also performed on non-pre-oxidized specimens after oxidation at 1000 and 1100 °C. All the pre-oxidized specimens showed enhanced oxidation resistance during subsequent oxidations, and this effect was stronger for the specimens pre-oxidized at higher temperatures. After subsequent oxidation at 1000 °C for 5130 s, all the pre-oxidized specimens showed higher ductility than the non-pre-oxidized specimen. This was largely due to the enhanced breakaway oxidation resistance by the preformed oxides. In addition, after subsequent oxidation at 1100 °C, the specimens pre-oxidized at 900 and 1000 °C showed higher ductility than the non-pre-oxidized specimens, whereas the specimens pre-oxidized at 1100 and 1200 °C exhibited lower ductility. Even though pre-oxidation at higher temperature was better for enhancing oxidation resistance, pre-oxidation at lower temperature was better for the ductility. To analyze this tendency, oxide thickness and macro-hardness of metal substrates were measured from the specimens which were subsequently oxidized at a same condition. As the pre-oxidation temperature increased, the oxide thickness decreased, and the macro-hardness increased. Considering that macro-hardness is related to the oxygen concentration in the metal substrate, the lower ductility at higher pre-oxidation temperature was due to that the specimens pre-oxidized at higher temperature contained higher concentration of oxygen in the metal substrates.