Effect of Corrosion Product Deposition on Heat Transfer of Plate Fuel Assembly

Plate fuel assemblies are widely used in various small modular reactors and marine reactors due to its compact structural design and high heat transfer efficiency. The deposition of corrosion products on the surfaces of the fuel plates significantly increases the thermal resistance between the coolant and the fuel, thereby increasing the cladding temperature and compromising reactor safety margins. Currently, quantitative investigations of this process in plate fuel assemblies remain limited. This study aimed to establish a corrosion deposition model to investigate the effect of corrosion product deposition on the heat transfer performance of plate fuel assemblies. A predictive mathematical model was developed to estimate the deposition rates of both soluble and insoluble corrosion products on the fuel surfaces, along with the erosion rate induced by the coolant, which were the three main mechanisms governing the deposition process. A thermal resistance model was also established to simulate the evolution of heat transfer resistance caused by deposition over time. The above theoretical models were implemented into the basic equations of computation fluid dynamics (CFD) software Fluent to achieve pseudo-transient coupled computations of deposition, erosion, flow, and heat transfer processes. The proposed model was then validated against experimental data to demonstrate its excellent performance in predicting the deposition amount and the resulting thermal resistance. Subsequently, the deposition behavior and its impact on heat transfer in plate fuel assemblies were investigated, and the influence factors were explored, including different inlet flow velocities and power densities. The results show that the deposition thickness increases gradually over time until a dynamic equilibrium is established between corrosion product deposition and coolant erosion. The deposition rate of soluble ions increases with rising deposition layer temperature and decreasing wall shear stress, while the erosion rate by coolant increases proportionally with both flow velocity and power density. Higher power density will increase the cladding temperature of fuel assemblies, which enhances the deposition of soluble ions and thereby increases the net deposition amount. The inlet flow velocity significantly affects the deposition amount after reaching equilibrium, and the time period to reach the dynamic equilibrium condition. Increased coolant flow velocity accelerates the stabilization of deposition thickness and reduces the equilibrium deposition thickness. The thickness of deposition layer exhibits non-uniform distribution, with localized thickening in high-temperature regions, particularly along the midline of the fuel plate. A significant temperature rise on the fuel surface is observed due to corrosion deposition. At low flow velocity in this paper, the average thickness of corrosion product reaches 20.14 μm, causing a maximum temperature rise of 17.7 K on the cladding surface relative to the non-fouled condition. The simulation methodology and obtained results can provide a valuable reference for the design, safety analysis, and long-term operation of plate fuel assemblies in advanced nuclear reactors.