Evaluation of homogenisation error in two-group nodal diffusion calculation for VVER-1000 core

A two-dimensional benchmark problem for a VVER-1000 hot zero-power state with fresh fuel loading is presented. The reference solution has been obtained by many-group heterogeneous transport-theory calculations with the code Mariko, applying the method of characteristics. An equivalent two-group diffusion problem has been defined by homogenized two-group diffusion parameters and discontinuity factors for the fuel assemblies and the radial reflector nodes. The two-group nodal neutron diffusion model DYN3D has been verified against this benchmark. The DYN3D errors in the relative assembly-wise power distribution vary between -1.6 % and +1.1 %, the deviation in k-eff is –50 pcm.