Neutronic analysis of an EPR core employing PaO2 and NpO2 as burnable absorber coatings

This study investigates the use of Protactinium oxide (PaO 2 ) and Neptunium oxide (NpO 2 ) as regenerative burnable-absorber coatings for improving long-cycle reactivity control in a European Pressurized Reactor (EPR) fuel core. The proposed concept applies thin PaO 2 and NpO 2 layers to (Th- 233 U)O 2 Integral Fuel Burnable Absorber (IFBA) fuel rods and evaluates their neutronic performance relative to conventional UO 2 +Gd 2 O 3 and (Th- 233 U)O 2 +Gd 2 O 3 (thorium-based) reference designs. Using the full-core SERPENT continuous-energy Monte Carlo code simulations, key parameters including burnup behavior, fissile-inventory retention, neutron-flux spectrum, radioactivity buildup, and actinide/fission-product evolution are assessed. Safety-related indicators such as fuel-temperature, moderator-temperature, and boron-worth coefficients are also examined to determine the impact of regenerative transmutation on inherent stability. The results show that, although the coated cases exhibit higher BOC k eff than the Gd-bearing reference cores (because the coated designs are gadolinia-free), PaO 2 /NpO 2 coatings produce a steeper early-cycle reactivity burn-down and reduce the overall reactivity swing, while sustaining higher reactivity at extended burnup through in-situ formation of 233 U and 239 Pu. These coatings promote smoother power distribution, stronger boron worth, and reduced reactivity swing compared with Gd-bearing fuel, while yielding lower cumulative radioactivity. Overall, the findings indicate that PaO 2 and NpO 2 coatings offer a promising pathway for enhancing fuel-cycle economy, safety coefficients, and reactivity management in Generation III+ light-water-reactor cores.