An investigation of the effects of neutron energy-group structures and resonance treatment in a fusion–fission hybrid reactor fuelling with Tho 2

Abstract

In this work, the effects of neutron energy-group structures and resonance treatments on the main integral neutronic parameters are investigated in a fusion–fission hybrid reactor, which has a fast and a thermal blanket fuelling with ThO 2. A D–T fusion neutron (14.1 MeV) is used as a neutron source. Fissile zone is cooled: (a) with light water for the moderated blanket and (b) with pressurized helium gas for the fast blanket. The neutronic parameters have been evaluated with and without a resonance treatment for the same blanket compositions for the sake of a consistent comparison. The study has shown that neutron reactions above a threshold energy in fast neutron groups are less sensitive to resonance treatment, such as 7Li(n,αn′)T and 232Th(n,f). Neutron energy-group structures in the neutron libraries and description of fusion neutron source spectrum mainly affect these reactions. On the other hand, neutron reactions in the resonance and thermal energy groups are sensitive to resonance treatment, such as 6Li(n,α)T and 232Th(n,γ), depending on the resonance structures. In the fast blanket calculations, resonance-based errors are lower and neutron source based errors are higher than in the moderated blanket. Furthermore, a correct description of the fusion neutron source spectrum over several neutron energy groups is essential to calculate fission reaction rates, fission heating density, fusile and fissile breeding rates and neutron leakage accurately.