Influence of double-beam design on nuclear waste transmutation performance for CiADS-like reactor

This study establishes neutronics models of both single-beam and double-beam driven ADS subcritical reactors based on the CiADS core geometry using the OpenMC code, systematically comparing their performance in terms of power distribution, neutron flux, transmutation of long-lived fission products (LLFPs), and breeding of plutonium. Comparison shows that the discrepancy in the effective neutron multiplication factor between the model and reference results is within ± 0.003, and the neutron energy spectra agree well in the range of 1 0 − 4 MeV to 10 MeV. The results indicate that the double-beam design significantly improves the axial power distribution uniformity, with the full width at half maximum increasing from 58.8 cm in the single-beam system to 60.5 cm in the double-beam system, along with a general increase in neutron flux within fuel assemblies. Regarding transmutation performance, the double-beam system enhances the transmutation rate of 135 Cs in LLFP assemblies by 58% and significantly promotes the breeding of 239 Pu. These findings demonstrate that the double-beam design offers clear advantages in improving power flattening, enhancing transmutation efficiency, and promoting actinide conversion in ADS systems, providing neutronic insights for future engineering conceptual design of multi-beam ADS configurations.