Suitable Choice of Angular Current Approximations for 2-D Neutron Transport

Abstract

The success of interface current and response matrix methods of approximately solving the integral neutron transport equation depends on the adequacy of the angular current approximation used in representing subregion interface currents. A program RICANT has been developed to solve the neutron transport equation by interface current method in 2-D rectangular geometry. Angular dependence of interface currents is accounted by P_N half-space expansions. The results of RICANT are compared with those of other neutron transport methods to determine the suitability of different orders of P_N half-space expansions in analysing 2-D problems. It is found that the use of P₂ half-space expansions is necessary to get reliably accurate results. It is also found that the use of a four term expansion almost reproduces the results of using the full P₂ half-space expansion. These conclusions are applicable to response matrix method for solving the neutron transport equation also, where the subregion surface currents are similarly expanded. Hence, this four term expansion is recommended as a suitable choice of angular current approximation in 2-D LWR lattice problems.