Testing of the symmetry options in the linear surface method of characteristics for VVER-1000 assembly calculations

The generation of multi-parameter nodal cross-section libraries for nuclear reactor cores of VVER type requires multiple depletion and branch calculations of fuel assemblies with heterogeneous cells. In order to ensure good accuracy and acceptable calculation time, it is important to use some of the symmetry options for hexagonal geometry. The objective of this work is to test the performance of the 600 rotational symmetry and axial reflection options in the Linear Surface Method of Characteristics in APOLLO2, as applied to VVER-1000 assembly calculations. A fuel assembly with the control rods inserted was used as a test case. Results obtained with the 600 symmetry options in 281 energy groups were compared to whole assembly APOLLO2 solutions and TRIPOLI4 continuous energy Monte Carlo solutions. The results show that the 600 rotational symmetry is a suitable option for practical calculations, with acceptable accuracy and computational efficiency. Key words: VVER-1000, assembly calculations, APOLLO2 code, linear surface method of characteristics, symmetry options