High-Temperature Steam Oxidation Behavior of Zr-xSn-0.35Fe-0.15Cr Alloys Under Simulated Loss of Coolant Accident Conditions

Abstract:

Zirconium alloy cladding will undergo high-temperature steam oxidation in a loss of coolant accident to make it be brittle, thereby leading to rupture due to absorbing oxygen, which will affect the safe operation of nuclear reactors. The high-temperature steam oxidation behavior of Zr-xSn-0.35Fe-0.15Cr (x=0.5, 0.75, 1.0, 1.2 and 1.5, wt%) alloys at 800–1200 ℃ was studied by a synchronous thermal analyzer equipped with a steam generator. The cross-sectional microstructures of the samples after high-temperature steam oxidation were observed by OM, and the O content was tested by EPMA. Results show that the high-temperature steam oxidation resistance and oxidation kinetics of zirconium alloys show a certain regularity with Sn content at different temperatures, which is mainly related to the action mechanism of α-Zr? β-Zr and m-ZrO₂?t-ZrO₂ phase transformation behavior of zirconium alloys. As the oxidation temperature increases, the oxidized alloy samples present a double-layer structure of ZrO₂ and α-Zr(O), accompanied by the appearance and disappearance of the mixed layer structure of β-Zr+α-Zr(O), which is caused by the effect of O on the α?β phase transformation. The increase in Sn content inhibits the diffusion of O from α-Zr to β-Zr. From the perspective that the increase in Sn content affects the α-Zr?β-Zr phase transformation and inhibits the diffusion of O from α-Zr to β-Zr, the mechanism of the effect of Sn content on the high-temperature steam oxidation behavior of zirconium alloys at different temperatures was discussed.