基于COMSOL Multiphysics的中子扩散问题求解以及气冷微堆应用分析

Solution of Neutron Diffusion Problem Based on COMSOL Multiphysics and Its Application Analysis on Micro Gas-cooled Reactor

基于三维有限元程序COMSOL Multiphysics的“系数形式偏微分方程接口”开发了中子扩散方程的求解模型,利用COMSOL Multiphysics的特征值和瞬态求解器分别对稳态和瞬态中子扩散方程进行了求解。通过与二维的2D-TWIGL基准题(包括稳态和瞬态工况)以及三维的3D IAEA PWR基准题的计算结果进行对比,验证了所开发中子扩散方程求解模型的正确性。针对气冷微堆堆芯进行建模,采用蒙特卡罗程序RMC生成双群和25群的群常数,利用该中子扩散求解模型开展了气冷微堆堆芯临界计算,结果分别与连续能量和多群蒙特卡罗计算参考值进行对比。结果表明:得到的有效增殖因数以及三维功率分布总体上能与对应的多群蒙特卡罗参考值较好吻合。与连续能量蒙特卡罗参考值相比,采用25能群的结果较双群划分方式更为准确。对于气冷微堆堆型,能群结构划分方式对结果精度的影响显著。采用精细能群划分能改善计算精度,但会使得求解所需资源和时间大幅上升。

As the cornerstone of the development of the computational tool for the coupled neutronics and thermal-hydraulics analysis dedicated to the micro gas-cooled reactor,neutronic diffusion solver was developed in this work based on the generic 3D finite-element CFD code COMSOL Multiphysics by taking advantage of its equation-based modeling functionality“coefficient form PDE interface”.The steady-state and transient neutronic diffusion equations are solved using the eigenvalue solver and transient solver of this code,respectively.The neutronic diffusion solver developed in this work was firstly validated against two benchmark problems,i.e.2D-TWIGL and 3D IAEA PWR problems respectively.The comparison of the calculation results of this solve with the reference values offered by the corresponding benchmark problems is satisfactory.Thereafter,this neutronic diffusion solve was applied to the micro gas-cooled reactor criticality analysis,with the group constants(including two-group and 25-group)generated by the Monte-Carlo code RMC.The calculation results of neutronic diffusion were also compared with the reference values derived by the Monte-Carlo transport calculations using the RMC code based on both continuous-energy-spectrum and multi-group methods.In general,the results obtained by solving both the two-group or 25-group neutronic diffusion equations,such as effective multiplication factor and three-dimension power distribution,can match well with the corresponding multi-group Monte-Carlo simulation.Whereas when comparing with the continuous-energy-spectrum Monte-Carlo results,adopting the 25 energy groups is able to gain better accuracy in contrast to the two energy groups,indicating that the energy-group division has a significant impact on the neutronics for the micro gas-cooled reactor.The accuracy of prediction can be improved by adopting a more sophisticated energy group structure.However,the required computational source and time will dramatically increase with the number of energy groups.