Benchmarking of COBAYA3 pin-by-pin for VVER

This paper presents results of the benchmarking of COBAYA3 pin-by-pin for VVER-1000 obtained in the frame of the EU NURISP project. The 3D lattice solver in COBAYA3 uses transport corrected multi-group diffusion approximation with side-dependent interface discontinuity factors of GET or Selengut Black Box type. The objective of this study is to test the few-group calculation scheme when using structur ed and unstructured spatial meshes. Unstructured mesh is necessary to model the water gaps between the hexagonal assemblies. The benchmark problems include pin-by-pin calculations of 2D subsets of the core and comparison with APOLLO2 and TR IPOLI4 transport reference solutions. COBAYA3 solutions in 2, 4 and 8 energy groups have been tested. The results show excellent agreement with the reference on es when using side-dependent interface discontinuity factors.