Coupled Neutronics-thermal-hydraulics Simulation of Nuclear Reactor Based on Lattice Boltzmann Method

Abstract

To analyze the internal behavior of the nuclear reactor core accurately and reliably, the multiphysics coupling effect should be considered, mainly including the neutronics, the fluid flow and the heat transfer processes. However, due to the strong differences between different physical fields, the multiphysics coupling simulation shows great difficulty, and it is always realized using the external coupling method with different codes for different fields. To improve this condition, the presented work established a lattice Boltzmann model to solve the coupled neutronicsthermalhydraulics process, which could use a similar lattice Boltzmann method (LBM) to realize internal coupling to solve the different physical fields. The neutron transport process was simulated using the LBM model for all the neutron transport SN, SP3 and diffusion approximations. To comprehensively consider both the solid and liquid fuel reactors, the LBM was used to solve the delayed neutron precursor balance process and heat transfer process with considering the convection effect. For general flow conditions, including the laminar and turbulence flows, the LBM model based on largeeddy simulation was considered. Under the similar LBM implementation of different physical fields, the difficulty of multiphysics calculation was greatly reduced. The simulations of different physical fields were all realized along with the similar LBM implementation including “collision” and “streaming” processes, which means that a similar solver could be used for all these different physical processes. The interaction and feedback between different fields were realized using the LBM functions and no external data transfer and interpolation were required anymore, which showed obvious advantages in comparing with other external coupling methods. The accuracy and applicability of the proposed LBM model were verified by simulating the typical benchmark under different Reynold numbers, and the results show high accuracy comparing with the direct numerical simulation solutions. After that, the coupled LBM model was used to solve the fully coupled neutronicsthermalhydraulics problem of a simplified molten salt reactor. The influence of temperature feedback and fluid velocity was analyzed. Simulation results show that the LBM model can be used to solve the multiphysics process in a fluid fuel reactor. The temperature feedback has a strong effect on the hightemperature reactor, while the fluid flow also has an obvious effect on the neutronics process by affecting distributions of delayed neutron precursor and temperature. Increasing the flow velocity can effectively improve the heat transfer condition and, correspondingly, flatten temperature and power distribution, which is beneficial to nuclear reactor core safety. This work can provide a novel perspective for nuclear reactor multiphysics simulation. More physical fields can be further considered under the same LBM model with similar implementation.

Keywords

• coupled neutronics-thermal-hydraulics
• lattice boltzmann method