Zr-xSn-0.35Fe-0.15Cr合金在模拟失水事故下的高温蒸汽氧化行为

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

摘要:

锆合金包壳在失水事故中会经历高温蒸汽氧化，因吸氧使锆合金包壳脆化而发生破裂，影响核反应堆的安全运行。通过配备蒸汽发生器的同步热分析仪研究了Zr-xSn-0.35Fe-0.15Cr（x=0.5、0.75、1.0、1.2和1.5，wt%）5种锆合金在800~1200 ℃的高温蒸汽氧化行为，采用金相显微镜对高温蒸汽氧化后的样品横截面进行观察，使用电子探针显微分析仪进行O含量测试。结果表明：不同温度下，锆合金的抗高温蒸汽氧化性能和氧化动力学与Sn含量呈现一定规律，主要与锆合金的 α-Zr?β-Zr和m-ZrO₂?t-ZrO₂相转变行为作用机制有关。随着氧化温度的升高，合金氧化样品横截面呈现ZrO₂、α-Zr(O)双层结构，中间伴随着β-Zr+α-Zr(O)混合层结构的出现与消失，这是O对α?β相转变的影响造成的。从Sn含量增加影响α-Zr? β-Zr相变和抑制了O从α-Zr→β-Zr中扩散的角度，探讨了Sn含量对锆合金不同温度下高温蒸汽氧化行为的影响机制。

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.