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

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 lead-bismuth 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.