SIMULATE5 extensions for VVER analyses

Studsvik s in-core fuel management code package CMS/CMS5 has been in use in the industry for the square lattice LWR reactor analysis for more than 35 years. The lattice physics code CASMO5 has had the hexagonal geometry capability and been used for special applications and coupled to external nodal codes. Recent work started at Studsvik extends the hexagonal calculation capability to the nodal code, SIMULATE5, for the analysis of VVER 1000 and VVER 1200 s. CASMO5 is used for generating nodal cross-sections data from single assembly calculations. SIMULATE5 is a 3-D, steady-state, nodal code. The VVER extension solves the multi-group diffusion equation, or optionally SP3 equations, for the hexagonal-z geometry by dividing each hexagonal into six triangles. In each triangle, the Fourier solution of the wave equation is approximated by eight plane waves to describe the intra-nodal flux accurately. The cross sections are described by a hybrid microscopic-macroscopic model that includes approximately 60 heavy nuclides and fission products. Heterogeneities, due to spacer/grid and control rod, in the axial direction of an assembly are treated systematically. The paper summarizes the physics models employed in SIMULATE5 as well as the preliminary benchmarking activities. (author)