基于广义等价理论CMFD加速的2D MOC/1D S_(N)算法的收敛性改进研究

Convergence Optimization of 2D MOC/1D S_(N)Method via Generalized Equivalence Theory Based CMFD Acceleration

基于广义等价理论的CMFD(GET-CMFD)方法具有较好的收敛性,并成功应用到基于轴向节块展开法(NEM)的2D/1D算法中。然而,当采用具有更高精度的离散纵标法(S_(N))作为轴向求解器时,2D/1D算法面临不收敛的问题。为了解决此问题,本文针对采用各向同性泄漏项和各向异性泄漏项2种情况,对GET-CMFD中的轴向节块不连续因子(NDF)和轴向修正扩散因子(MDF)进行改进,同时对2D/1D耦合算法中关键的泄漏项分割技术的使用条件进行系统研究。计算结果显示:GET-CMFD方法中轴向NDF和轴向MDF采用2D MOC计算归并的通量进行计算,同时2D/1D算法中泄漏项采用最新更新的数值可以获得好的收敛性。泄漏项分割方法的使用条件采用出射角通量小于0修正可以在保证收敛性的同时降低精度损失。在一次2D/1D迭代过程内采用2次S_(N)计算可以在计算量几乎不提升的前提下,显著降低迭代次数,提高收敛性。通过对GET-CMFD方法,泄漏项分割技术使用条件以及迭代流程的改进,算法的收敛性可以得到明显提高。

The generalized equivalence theory based CMFD(GET-CMFD)has great convergence behavior and has been successfully applied to the axial NEM based 2D/1D coupling method.However,when applying the high precision S_(N)as the axial solver,the 2D/1D coupling method faces the convergence problem.To solve this problem,in the case of isotropic transverse leakage and anisotropic transverse leakage,the source of the scalar flux of axial nodal discontinuity factor(NDF)and axial modified diffusion factor(MDF)in the GET-CMFD are optimized.At the same time,the application conditions of the transverse leakage splitting method in 2D/1D coupling method are studied systematically.The results show that by adopting the scalar flux from 2D MOC calculation for the axial NDF axial and MDF in the GET-CMFD equation and adopting the latest updated value of leakage term,2D/1D coupling method can obtain good convergence.The application condition of the transverse leakage splitting method is that the outgoing angular flux is less than 0,which can guarantee convergence and reduce the precision loss.At the same time,using S_(N)calculation twice in a 2D/1D iteration can significantly reduce the number of iterations without increasing the computational load.By improving the GET-CMFD equation,the leakage splitting method and the iterative process,the convergence of 2D/1D coupling method can be improved obviously.