Performance analysis of zirconium alloy after long-term cooling after simulated LOCA test

During the standard operation of the reactor, the zirconium alloy cladding continues to absorb hydrogen due to water corrosion. The zirconium alloy cladding, which has been embrittled by the hydrogen absorption, will experience more severe embrittlement after experiencing a loss of coolant accident (LOCA). The subsequent long-term cooling process will further corrode the cladding and make it unable to maintain a geometry suitable for cooling. To better simulate the actual operating conditions, pre hydrogen Zr-Sn-Nb zirconium alloy was selected and subjected to the high-temperature steam oxidation quenching test to replicate the LOCA accidents. Then, a long-term cooling environment was simulated through an overheated steam environment. The residual plasticity of the sample was measured post the test, alongside with analyzing the microstructure morphology and oxygen element distribution of the sample through various microscopic analysis methods. The results show that after long-term cooling, the oxidation of zirconium alloy cladding intensified. The oxide films on the samples remain monoclinic phase after the long-term cooling, even the newly formed oxide film at the interface is monoclinic as well; the oxygen-rich α (O) layer of zirconium alloy transforms into a new oxide film after long-term cooling, while the oxygen content in the prior- β layer increases The increase in oxygen content in the layer exacerbates the embrittlement of zirconium alloys.