Optimization approach of energy group structure for the Canadian pressure tube supercritical water reactor

Reactor physics calculations implement several approximations that aim to provide an accurate solution of the linear Boltzmann equation. One of these approximations is an energy discretization in which the neutron cross-sections are averaged over an energy interval and treated as an energy independent parameter within that interval. In order to simplify the full-core diffusion calculation, an additional energy group condensation is traditionally performed that creates a simpler few-group structure (typically 2 group for thermal reactors) from an initial fine/many-group structure. The Canadian PT-SCWR is a Generation IV reactor concept that uses supercritical water as coolant. Features include bi-directional coolant flow through the High-Efficiency Re-entrant Channel and a fuel mixture of plutonium and thorium. Historically mixed oxide and high temperature reactor applications have required more than 2-group simulations to provide reasonable accuracy. This work presents a systematic approach to the optimization of energy group structure for the Canadian PT-SCWR and analyzes the applicability of the traditional two neutron energy group structure that is typically applied in diffusion calculations using tools within the SCALE code package.