Boundary Conditions to Describe the Reactor Reflector

To exclude the reflector region during core calculations, the relationship between group currents and fluxes is investigated in a 60-deg homogeneous sector. With given normal currents on the boundary, a two-dimensional analytical solution to the four-energy-group diffusion equation is derived. Furthermore, a numerical procedure is presented to calculate the flux distribution on the boundary, with a given normal current distribution there. Numerical results are presented to illustrate the coupling between fine-mesh cell edges and between energy groups, as well as to illustrate the impact of the current distribution on the flux distribution.