Generation method and verification of pebble type VHTR multigroup cross sections based on OpenMC.

• A Monte Carlo based generation method of multigroup cross sections for pebble type VHTR by OpenMC was developed. • The new method can effectively deal with the double heterogeneity effect of pebble type VHTR. • Two different level models are proposed to be used to assess the accuracy of the cross section generation method. • Neutronics calculation results using multigroup cross sections by homogenized model was obtained. Very high temperature reactor (VHTR) is a Generation-IV (Gen-IV) type of reactor which could nominally operate at a high temperature. In traditional two-step core neutronics calculation method of VHTR, the high precision multigroup cross sections are required. Therefore, a new Monte Carlo based generation scheme for multigroup cross sections of pebble type VHTR, based on open source code OpenMC, is proposed in this paper. The new method can effectively deal with the double heterogeneity effect of pebble type VHTR. And the generated multigroup cross sections can be applied to the deterministic neutronics calculations and OpenMC multigroup calculations. Moreover, a unit cell model and a simplified pebble bed lattice model of VHTR were developed to be used for verification of the method. According to the verification results, the new developed method using OpenMC to generate multigroup homogenized cross sections for pebble type VHTR is feasible and enough accurate. [ABSTRACT FROM AUTHOR]