Coarse-Mesh Nodal Methods with the Capability to Explicitly Handle the Material Heterogeneity in the Axial Direction of a Fuel Assembly

The incapability to handle the heterogeneity introduced by spacer grid and partially-inserted control rod has long been considered as one of the noticeable defects for the conventional coarse-mesh nodal methods. To improve this defect, two new nodal methods with the capability to explicitly handle these heterogeneities in the framework of coarse-mesh nodal methods are proposed. Numerical results for IAEA 3D benchmark problem and the practical power reactor problems demonstrate that the proposed sub-mesh method is quite successful, it is able to effectively handle not only the partially inserted control rod, but also the fine spacer grid within an axial coarse mesh.