Numerical Study on Molten Stainless Steel and Lead Bismuth Eutectic Interaction for Lead-Cooled Fast Reactors Using the ACENA Code With Experimental Validation
Authors: Fan Shuowang , Chen Yutong , Zhang Dalin , Wu Xiaoli , Tian Wenxi , Qiu Suizheng , Su Guanghui 
Published: November 2024

Abstract
The LBE- or Lead-cooled fast reactor (LFR) is an important candidate reactor for the Generation-IV nuclear energy systems, where the Molten Fuel-Coolant Interaction (MFCI) process differs from that occurred in light water reactors and sodium cooled fast reactors due to the coolant property differences. In the lack of experimental and numerical studies on MFCI process in LFRs, the experiments under eight conditions with different initial temperatures of molten metal and different depth of coolant pool are conducted in this study to research the interaction between molten stainless steel (SS) and liquid Lead Bismuth Eutectic (LBE) coolant, where the radial and axial temperature distribution data of the LBE pool are obtained to validate a 2D multiphase fluid dynamics code named ACENA, which is preliminarily developed to simulate severe accidents phenomena for heavy liquid metal cooled fast reactors. A brief description of theoretical models employed in the ACENA code is listed in this study. The comparison results show the ACENA code could attain acceptable accuracy in simulating flow and heat transfer characteristics of MFCI process. The calculated values of temperature growth peak in the LBE pool are in good agreement with the experimental data. The overall maximum deviation between the calculated and experimental temperature increase values is within the range of 10–30 K. The maximum pressure surge of the argon atmosphere covering the LBE pool does not exceed the safety limit of the reaction vessel predicted by the ACENA code corresponding to the experiment conditions. However, due to the severe electromagnetic interference during the induction heating process in experiments, the relatively accurate pressure fluctuation data were failed to be collected. According to this study, the shortcomings of the current numerical work are summarized as follows: (1) The code assumes the molten material could be fully mixed with the coolant in the control grid, so the solidification and fragmentation phenomena of the molten material could not be realistically simulated, especially for the large-sized products obtained from experiments; (2) The code assumes the reaction vessel is adiabatic and the temperature distribution of the LBE pool is uniform, but actually the temperature of LBE pool was manually adjusted to approximate thermal equilibrium. Additionally, due to the heat dissipation of the molten SS in the crucible, a thermal stratification phenomenon occurred in the LBE pool; (3) The code employs empirical formulas validated in SFRs research, while due to the physical property differences of sodium and LBE, the empirical formulas may not be completely applicable to LFRs if only by simply extrapolating. Therefore, further experimental studies and improvement of physical models are necessary for excavating potential of the ACENA code, which could close some research gaps for accident safety analysis of LFRs.