The influence of an energy groups number and mesh size on results of reactivity coefficients calculations for BN-600 benchmark core. Appendix 1

This document presents the OKBM contribution to the analysis of a benchmark of BN-600 reactor hybrid core with simultaneous loading of uranium fuel and MOX fuel within the framework of the international IAEA Co-ordinated Research Project (CRP) on 'Updated Codes and Methods to Reduce the Calculational Uncertainties of the LMFR Reactivity Effects'. The purpose of the present document is the comparison of some obtained for the Phase 2 results using the different energy groups number and the different mesh point size. The CRP participants at calculation of a benchmark used different planar mesh point sizes. The axial mesh point size was not stipulated, but the mesh sizes were specified for the desired results representation. Therefore in some cases there was possible the application of rather large axial mesh size. The discrepancy in results because the different mesh point size using should be estimated. The results of some participants were obtained using the relatively small energy groups number - 6, 9, and 12. The influence of the energy group number on value of the obtained reactivity coefficients is analyzed in case of the OKBM calculations results. Besides in case of the sodium density reactivity coefficient the OKBM used method of the choice for the few group optimal division of the energy scale is shown. The probable additional uncertainties as the consequence of the baseless group division are estimated by the comparison of the group division schemes applied by different CRP participants