基于格子Boltzmann方法的反应堆核-热-流耦合模拟

反应堆堆芯内部存在多种不同物理场之间的相互作用和反馈，对其准确模拟需要考虑这些物理过程之间的耦合。为了降低堆芯核 热 流耦合模拟的实现难度，消除不同物理场之间的外部插值过程，本文构建了核 热 流耦合模拟的格子Boltzmann方法（LBM），将中子输运（包括SN方程、SP3方程以及扩散方程）、考虑燃料流动效应的缓发中子先驱核守恒方程以及流动传热方程统一到相似的LBM格式下，采用统一的LBM碰撞 迁移过程进行求解，有效降低了堆芯多物理耦合模拟的实现难度。计算结果表明：本文建立的核 热 流耦合LBM模型对不同雷诺数下的流动效应均能准确模拟，同时温度反馈在高温熔盐堆低速流动条件下有较为明显的影响，不能忽略；提高堆芯熔盐流速能够有效地展平功率及温度分布。

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

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.