AN ANALYSIS OF A HETEROGENEOUS CORE USING GREEN-FUNCTION

A nodal method to solve the multi-group diffusion equation is given to treat the heterogeneity of fuel assemblies of reactors. Nodal equations of 3-point form in each coordinates are derived for the diffusion equation in one dimensional slab and x-y geometries using Green's function whose unknowns are only fluxes at the boundary surfaces of assemblies. Coefficients of the nodal equations are given by the boundary values of Green's function, which are also obtained by solving 3-point difference equations in each coordinates for the heterogeneous assembly regarding it as being isolated. In the present method, it is not necessary to use homogenized cross sections for the assembly, and the heterogeneity in the fuel assembly and interaction effect between assemblies can be taken into account.