Neutronic and thermal–hydraulic coupling of FCM and helium annular fuel as accident-tolerant fuel

• Both ATFs had lower peak fuel temperature (Helium: −25.3 %, FCM: −42.2 %). • Helium annular fuel boosts cycle length by 24.2 % for same 235 U content. • FCM shows shorter cycle; key parameters reported. • Pin power peaking of ATF fuel assemblies similar to reference. • Convergence achieved on average after 8 iterations with max power errors below 2 % The study aims to explore two types of Accident Tolerant Fuel (ATF) (helium annular fuel and Fully Ceramic Microencapsulated (FCM) fuel), both with Silicon Carbide (SiC) used as clad material and as a matrix material for TRISO (TRi-structural ISOtropic particle fuel) particles in FCM fuel. The safety characteristics (such as maximum fuel temperatures) were evaluated and compared against reference UO 2 -Zr for a Pressurised Water Reactor (PWR) with neutronic and thermal–hydraulic coupling during normal operation for fresh fuel. The results show that both annular and FCM fuels exhibit reduced maximum temperatures compared to the reference fuel, with a reduction of 479 K (25.3 %) for helium annular fuel and 798 K (42.2 %) in the FCM fuel. The annular fuel improved the burnup by 12.4 MWd/kgU (24.2 %) without the cycle length being affected significantly (−5.6 %). The FCM fuel significantly reduced in the cycle length by 44.1 % while the burnup was more than double the reference providing a 163.5 % increased burnup in comparison to the reference fuel assembly. Assembly pin power peaking factors showed no dramatic deviation from the reference and the axial power distribution of ATFs is more symmetrical than that of the reference fuels. In terms of coupling the pin models converged after eight iterations on average with maximum relative power errors per radial node below 2 %.