A new online energy group condensation method for the high-fidelity neutronics code NECP-X

•A new online group condensation method for the high-fidelity whole-core transport calculation is introduced.•The particle swarm optimization method is used to obtain the broad-group structure to preserve accuracy.•The numerical results show good performance of the developed method. The high-fidelity whole-core heterogeneous transport calculation attracts a lot of attention because of its high accuracy. However, too many energy-groups for the transport calculation lead to more computational time. This paper presents a new online energy group condensation (OGC) method to accelerate the whole-core heterogeneous transport calculation. Three different models are established for the fuel pin-cell, none-fuel pin-cell and reflector regions, to obtain the spectrum. For the fuel pin-cell regions, a one-dimension (1D) cylinder model is generated during the global–local resonance calculations, and the spectrum is calculated based on the equivalent 1D model and the macro cross-section is condensed based on this spectrum. For the none-fuel pin-cell regions, a super-cell model is established with this none-fuel pin-cell and its surrounding fuel, and the spectrum is calculated with the super-cell model. For the reflector regions, the fuel-lattice-reflector models are generated to calculate spectrum in reflector regions offline, and the spectrum is built-in for condensing the cross-sections for all reflector regions. The condensed energy group structure is studied with the particle swarm optimization (PSO) method to get a superior energy group structure with fewer group numbers but preserving accuracy. A set of benchmark problems are tested and the results show good performance of the new online group condensation method for the transport calculations.