Optimising the energy group structure used for fusion systems

► We calculate fusion relevant reaction rates using the point-wise estimator and multi-group energy binning approach. ► A 3 stage method optimising the energy group structure, for multi-group binning reaction rate calculations, is presented. ► The method is applied to fusion relevant materials. ► A fusion optimised energy grid is presented, called FOMG ( Fusion Optimised Multi-Group), with 16,000 energy bins. ► The FOMG structure presented is suitable for calculating activation and transport reaction rates within any fusion device.