2D core calculations for VVER-1000 with APOLLO2

The paper presents a stage of the validation of the APOLLO2 reference deterministic scheme for VVER. The objective is to assess the code solvers and the computational route for whole-core simulation. A specific objective is to test the higher-order characteristic method in APOLLO2. The test problem is a computational benchmark for a VVER-1000 2D core with fresh fuel loading. The core contains UOX and UOX + burnable absorber assemblies of six types. The domain of solution is 1/6 core sector with radial reflector. The benchmark represents un-rodded and fully rodded hot zero power states. Results for the state with all rods out are presented. A TRIPOLI4 Monte-Carlo solution with point-wise data and a MARIKO MOC solution from the benchmark specifications were used for comparison. Solutions with the step characteristic method (MOC) and the higher-order conservative linear surface characteristic method (CLS MOC) in APOLLO2 were analyzed. The results show that the higher-order method yields solutions close to the Monte-Carlo reference and is faster than the step characteristic method for whole core calculations. (authors)