Self-sustaining Thorium-fueled Reduced Moderation BWR Feasibility Study

This study assesses the feasibility of a thorium-based fuel-self-sustaining Reduced moderation BWR (RBWR-Th) core. This core features a hexagonal tight-lattice fuel, high exit coolant quality, axial segregation of seed and blanket regions, and compatibility with the ABWR reactor vessel inherited from the RBWR-AC proposed by Hitachi. The RBWR-Th differs from the RBWR-AC by eliminating the internal blanket, eliminating absorbers from the axial reflectors, replacing depleted urania with thoria as the primary fertile fuel and elongating the fissile region. When the Hitachi assumptions and correlations for thermal-hydraulic analysis are used, the RBWR-Th obtains an average core discharge burnup of 61 GWd/t versus 45 GWd/t for the RBWR-AC. However, when more conservative thermal-hydraulic correlations are used, the average discharge burnup drops to 25 GWd/t. The RBWR-Th maintains negative coolant void coefficients of reactivity throughout the cycle – between -155 and -131 pcm/% – but currently does not have sufficient margin for cold shutdown. Future studies will address this shutdown margin deficit and will account for coolant pressure drop constraint.