A comprehensive assessment of neutronic and thermal–hydraulic behavior of some advanced accident-tolerant fuels in solid and dual-cooled annular PWR assemblies

Accident-tolerant fuel (ATF) concepts are being evaluated to strengthen margins without sacrificing core economics. This study compares five ATF matrices, UN (with natural and enriched nitrogen), UC, UCO, U3Si2, and UAl2, implemented in 17 × 17 solid and 13 × 13 dual-cooled annular PWR lattices. Results show that the multiplication factor decreases monotonically with burnup in both geometries, which allows the use of the linear reactivity model to predict the reactor cycle length; UAl2 and UO2 provide the longest cycles. Assembly-level radial peaking remains low (≈1.05–1.09). All fuel and moderator temperature coefficients are negative, with the strongest feedback in annular UN (Natural N). Solid pins show a single outer-rim power/Pu-239 peak; annular pins split this into two milder rims and flatten the in-pin profile. Prompt (neutron-induced) power is essentially burnup-invariant by normalization, while decay heat grows with matrix density and conversion. Thermal-hydraulic results show that the annular geometry lowers coolant heating and pressure drop and raises the minimum DNBR by ∼ 55–65% relative to solid pins under identical boundary conditions. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.