Excess reactivity control using innovative burnable absorber configuration for a 24-month cycle APR-1400

Extending the fuel cycle from 18 to 24 months in Pressurized Water Reactors (PWRs) using LEU+ fuel (5 % ≤ U-235 ≤ 10 %) increases excess reactivity, requiring effective control to ensure safety and performance. This study evaluates various BA concepts—including gadolinia or erbia homogeneously mixed with fuel, ZrB₂ coatings, and highly intensive gadolinia/alumina burnable absorbers (HIGA)—to minimize CS usage while maintaining a 24-month cycle. Equilibrium core configurations were analyzed using CASMO-4E/SIMULATE-3. Results indicate that a hybrid approach, combining 0.75 w/o erbia homogeneously with fuel and 7 mol% HIGA BA rods, achieves optimal reactivity suppression while fulfilling safety criteria. This configuration effectively lowers CS concentration from 1357 ppm to 1151 ppm compared to a conventional Gd₂O₃ + UO₂ BA rod core, maintaining a stable reactivity coefficient range throughout the cycle. These findings support the feasibility of extending the APR-1400 fuel cycle while ensuring reactor safety and performance.