Pin power reconstruction for hexagonal geometry in nodal neutronics program Ants

The pin power reconstruction methodology for hexagonal geometry in the multigroup nodal neutronics program Ants is described and verified against full core Serpent Monte Carlo solutions in four VVER benchmarks. In order to provide the best possible reference solution, Serpent uses the same nuclear data libraries and simulation options both to generate the required group constants for Ants and to solve the full core reference solution. The root mean square of the relative differences in 2D pin powers between Ants and Serpent was between 0.83% and 1.11% in the four benchmarks, while the root mean square of the relative differences in the 2D intra-assembly peaking factor (Kk) was between 0.54% and 0.71%. Increasing the number of energy groups in the nodal solution tended improve the accuracy of the nodal solution as did the use of critical spectrum condensed group constant data instead of infinite spectrum group constants.