Neutronics-thermal-hydraulics-material coupling study of lead-bismuth cooled reactor single rod based on oxidative corrosion characteristics

[Background] Liquid lead-bismuth eutectic (LBE) corrosion and dissolution of structural materials pose significant challenges in the application of lead-bismuth-cooled fast reactors (LFRs). The use of oxygen as an inhibitor emerges as a promising approach to mitigate the corrosion of structural materials by liquid LBE. The oxidative corrosion in LFRs is influenced by various physical parameters within the reactor, including temperature, oxygen concentration, and time. Concurrently, the growth of the oxide layer on the cladding surface exacerbates the heat transfer between the cladding and the coolant, thereby influencing the thermal-hydraulic and neutron physics parameters of the core. Understanding the corrosion protection of structural materials and multi-physics characteristics is crucial issue for LFRs. [Purpose] This study aims to investigate the coupled mechanisms of neutron physics, thermal-hydraulics, and oxidative corrosion, along with the distribution of the oxide layer in lead-bismuth reactors. [Methods] A neutronics-thermal-hydraulics-material coupling framework was developed to investigate the variations in multi-physics parameters and oxide layer distribution in the LFR fuel rod under oxidative corrosion conditions. First of all, based on the Multiphysics Object-Oriented Simulation Environment (MOOSE), the framework was developed to couple three modules: neutron physics, thermal-hydraulics, and oxidative corrosion, and conduct simulation calculations. Thereafter, various lead-bismuth reactor oxide layer growth-removal models were encompassed into a MOOSE-based oxidative corrosion module, named Seal, and the Martinelli model was adopted in subsequent simulations after comparison with experimental values. Then, the neutron physics module was solved by the open-source neutron diffusion equation solver Moltres and the thermal-hydraulics module calculation was performed by MOOSE's Navier-Stokes and Heat Conduction modules. Two coupling relationships in the coupling framework, i.e., (1) the neutron physics module for transferring power distribution to the thermal-hydraulics module, and the thermal-hydraulics module transferring temperature distribution to the neutron physics module; (2) the thermal-hydraulics module transferring temperature field and flow field to the oxidative corrosion module, and the oxidative corrosion module transferring oxide layer thickness distribution to the thermal-hydraulics module, were investigated. Finally, the approach of simultaneously solving the coupled equations under the same mesh was employed for coupled calculations, with the control equations of the three modules solved simultaneously to achieve synchronized convergence of physical quantities. And the developed coupled framework was applied to perform benchmark calculations and sensitivity analysis of oxygen concentration for a lead-bismuth reactor fuel rod. [Results] The results indicate that: (1) after 10 000 h of oxidative corrosion under benchmark conditions, the average thickness of the oxide layer is approximately 10 μm, the maximum fuel temperature rise is 16 K, and keff decreases by 10-4; (2) an increase in oxygen concentration effectively inhibits magnetite dissolution but has a relatively minor promoting effect on the growth of Fe-Cr spinel. [Conclusions] This study demonstrates that the increase in oxygen concentration has a positive effect on the protection and self-healing ability of the oxide layer. It has both theoretical and practical significance for the development, design, and safety evaluation of LFR in China. © 2024 Science Press. All rights reserved.