The trigonal nodal SP3 method of the reactor code DYN3D

DYN3D is a 3D nodal diffusion code for steady-state and transient analyses of Light-Water Reactors (LWRs) with square and hexagonal fuel assembly geometries. Currently, several versions of the DYN3D code are available including a multi-group diffusion and a simplified P3 (SP3) neutron transport option for square geometry as well as a multi-group diffusion version for hexagonal geometry.
In this work, the multi-group SP3 method based on a trigonal-z geometry was developed. The method is applicable to the analysis of reactor cores with hexagonal fuel assemblies and allows flexible mesh refinement, which is of particular importance for VVER-type Pressurized Water Reactors (PWRs) as well as for innovative reactor concepts including block type High-Temperature Reactors (HTRs) and Sodium Fast Reactors (SFRs).
In this paper, the theoretical background for the trigonal SP3 methodology is outlined and the results of a preliminary verification analysis are presented by means of two VVER-440 single assembly test examples with different material compositions. The accordant cross sections and reference solutions were produced by the Monte Carlo code SERPENT. The DYN3D results are shown for 2 and 8 energy groups, respectively, and are in good agreement to the reference solutions. The maximum deviation in the nodal power distribution is about 1%.