A nodal SP3 approach for reactors with hexagonal fuel assemblies

The neutronics model of the nodal reactor dynamics code DYN3D developed for 3-D analyses of steady states and transients in light-water reactors has been extended by a simplified P3 (SP3) neutron transport option to overcome the limitations of the diffusion approach. To provide a method being applicable to reactors with hexagonal fuel assemblies and furthermore allowing flexible mesh refinement, the nodal SP3 method has been
developed on the basis of a flux expansion in trigonal-z geometry. Dividing a hexagonal fuel assembly into six triangular nodes, steady-state test calculations for one assembly as well as for a 'minicore' consisting of seven fuel assemblies have been performed, in which both a symmetric and an asymmetric material composition are chosen to be compared with more accurate HELIOS transport calculations in each case.