铅铋快堆堆芯包壳多场耦合腐蚀行为的数值模拟研究

Numerical Simulation of Multi-field Coupled Corrosion Behavior of Core Cladding in Lead-bismuth Fast Reactor

铅铋快堆中液态铅铋(LBE)腐蚀结构材料是制约铅铋快堆发展的关键难题之一,液态铅铋流动过程中对结构材料的侵蚀作用不可忽视。为开展高温液态铅铋环境下堆芯燃料包壳动态腐蚀特性研究,本文针对包壳管候选材料T91钢建立氧化、还原、侵蚀耦合腐蚀模型,结合计算流体力学(CFD)方法,对燃料包壳表面腐蚀现象进行模拟研究,并对影响腐蚀的关键因素进行分析。研究结果表明:一定铅铋流速下,燃料组件内沿液态铅铋流动方向,包壳表面温度越高,尖晶石层平衡厚度越厚,包壳厚度损失速率越高,运行800 h后,燃料组件仅剩出口处残留磁铁矿层;随着燃料组件入口液态铅铋流速的增加,包壳厚度损失速率越高;当入口流速为2 m/s,氧化层稳定情况下,中心棒的包壳厚度损失速率为0.044 98 mm/a;当燃料组件包壳表面氧浓度大于发生氧化反应的最低值时,包壳厚度损失速率随包壳表面温度升高而增加;当包壳表面氧浓度小于发生氧化反应的最低值时,包壳会直接被液态铅铋溶解,溶解速率高达上千mm/a。

Corrosion of structural materials in lead-bismuth fast reactors due to liquid lead-bismuth eutectic(LBE) is a significant issue that hinders their development.To slow down the corrosion rate of high temperature LBE on structural materials,it is crucial to precisely control the oxygen concentration in LBE,which can form a stable protective oxide layer on the surface of the structural materials.The high density of LBE means that its erosive effect on structural materials during flow cannot be ignored.To investigate the dynamic corrosion characteristics of T91 steel cladding tubes in a high-temperature LBE environment,a corrosion model that couples oxidation,reduction,and erosion was established.The computational fluid dynamics(CFD) method,along with the SST k-ω turbulence model and leadbismuth turbulence Prandtl number model were used.The simulation analysed the thermal-hydraulic characteristics of the fuel assembly,as well as the corrosion phenomenon of the fuel cladding surface.The analysis identifies the key factors that affect corrosion.The results indicate that at a specific flow velocity of LBE,the equilibrium thickness of the spinel layer increases with the rise in surface temperature of the cladding along the liquid LBE flow direction in the fuel assembly.Additionally,the thickness loss rate of the cladding also increases.At the end of 100 hours of service,the upper cladding of the fuel rod is covered by a double oxide layer consisting of magnetite and spinel.At the end of 800 hours of service,only the magnetite layer remains at the exit of the fuel assembly rod cladding.The surface of other cladding has only one spinel layer.As the liquid LBE flow velocity at the fuel assembly inlet increases,the cladding temperature decreases,but the cladding thickness loss rate increases due to the increase in wall shear stress.When the inlet flow velocity is 2 m/s and the oxide layer is stable,the center rod's cladding thickness loss rate is 0.044 98 mm/a.When the oxygen concentration on the surface of the cladding exceeds the minimum value required for the oxidation reaction,the cladding thickness loss rate increases with rising surface temperature.Conversely,when the oxygen concentration on the surface of the cladding is below the minimum value required for the oxidation reaction,the cladding dissolves in liquid LBE at a rate that can reach thousands of mm/a.This study proposes a numerical simulation method for predicting LBE core oxidation corrosion characteristics.The method can be used to accurately predict the corrosion of LBE cores.