Flux Expansion Nodal Method for Solving Neutron Diffusion Equations in Hexagonal-z Geometry
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摘要: 提出了一种在三维六角形几何节块内数值求解中子扩散方程的节块法。该方法把节块内各群中子注量分布用解析基函数近似展开。为了改善节块耦合关系,提出了一种新的节块边界条件:面平均偏流零次矩和一次矩同时保持连续。此外,将响应矩阵技术应用于迭代求解过程,使得该方法具有较高的计算效率。基于本文提出的模型,发展了三维六角形组件中子扩散计算程序FEMHEX。通过对二维、三维VVER基准问题校验计算表明,该方法能高效、准确的给出有效增殖系数以及节块功率分布。Abstract: A new flux expansion nodal method is developed to solve the neutron diffusion equations in hexagonal-z geometry.The intra-nodal flux distribution is expanded in a series of analytic basis functions for each group.In order to improve the nodal coupling relations,a new type of nodal boundary conditions is proposed,which simultaneously requires the continuity of both the zero-and first-order moments of partial current across the nodal surfaces.The response matrix technique is used,which gives a fast-running scheme for the iterative solution of the nodal diffusion equations.Based on the proposed model,the code FEMHEX has been developed and tested against 2-D and 3-D benchmark problems for the VVER-type reactors.The numerical results show that FEMHEX can predict accurately the multiplication factor and nodal powers.
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Key words:
- Hexagonal geometry /
- Neutron diffusion equation /
- Nodal method /
- Analytic basis function
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