Neutronic analysis of accident tolerant fuel concepts in spectral shift regulation conditions

The study of Accident Tolerant Fuels (ATFs) has gained significant attention due to their potential to enhance the safety and reliability of nuclear reactors, especially under severe accident conditions. This work investigates the neutron-physical performance of ATF concepts in Light Water Reactor (LWR) using spectral shift regulation (SSR). The SSR mechanism, which adjusts the moderator-to-fuel ratio, by means of mechanical displacers that run in the guide tubes, enables spectral hardening during the initial cycle and softening toward the end, optimizing fuel utilization and reactor safety. Using collision probability method with the GETERA simulation tool and BNAB library, this study evaluates various ATF designs, including chromium-coated zirconium (CrZry), FeCrAl alloys, and SiC composites, combined with uranium silicide (U 3 Si 2 ) and uranium nitride (UN) high density fuels. Key metrics such as infinite multiplication factor, nuclide inventory, and plutonium buildup are analyzed. Results demonstrate that SiC cladding paired with UO 2 or U 3 Si 2 fuels offers the best neutronic characteristics, requiring slightly lower uranium enrichment. Thin FeCrAl cladding, on the other hand, shows higher enrichment needs but still around enrichment level of the fuel in Light Water Reactors, when paired with combination with U 3 Si 2 . The integration of SSR in the LWR reactor improves burn-up efficiency while burning produced plutonium and lower natural uranium consumption, resulting in reduced waste. Among the ATF options studied, SiC cladding shows good promise for guide tube and displacer applications, due to their neutron transparency and thermal stability.