Analysis and design of a 333 mwth marine pwr core using mixed d2o-h2o coolant and thorium-based checkerboard micro-heterogeneous and all-uranium fuel

In this reactor physics study, we attempt to de-sign a soluble-boron-free (SBF) PWR civil marine re- Actor core that can operate over a 20 effective-full-power-years life at 333 MWth using mixed D₂O-H₂O coolant. We use WIMS to develop subassembly de-signs and PANTHER to examine whole-core arrange- ments, optimizing: subassembly and core geometry; fuel enrichment; burnable and moveable poison de-sign; and whole-core loading patterns. In this study, we use 15% U-235 enriched UO₂ and 18% enriched micro-heterogeneous ThO₂-UO₂ duplex fuel arranged in a simple checkerboard configuration. Comparisons are made between the homogeneously mixed 15% U-235 enriched all-UO₂ case and the checkerboard con-figuration with high thickness ZrB₂integral fuel burn- Able absorber pins for reactivity control. Taking ad- vantage of self-shielding effects, the checkerboard op-tion shows greater promise in the final burnable poi-son design while maintaining low, stable reactivity with minimal burnup penalty. For the final poison design with ZrB₂, the checkerboard contributes 2.5% more initial reactivity suppression, although the all-UO₂ design exhibits lower reactivity swing. All the candidate materials show greater rod worth for the checkerboard design. For both fuels, B₄C has the highest reactivity worth, providing 3% higher control rod worth for checkerboard fuel than all-UO₂. Fi-nally, optimized assemblies were loaded into a 3D re- Actor model in PANTHER. The PANTHER results show that the designed cores can achieve the target core lifetime of 20 years, confirming the fissile load-ing is well-designed.