Accident Tolerant Fuel (ATF) technologies have emerged in response to the safety limitations of conventional -Zr fuel systems in light water reactors (LWRs), particularly under high-temperature accident conditions, as highlighted by severe nuclear incidents at Three Mile Island Unit 2 and the Fukushima Daiichi Nuclear Power Plant. The primary motivation is to minimize hydrogen generation in the cladding and enhance the thermal conductivity of the fuel, thereby increasing reactor resilience under extreme conditions while maintaining or improving fuel performance during normal operation. To this end, uranium mononitride (UN) fuel and silicon carbide (SiC) cladding were selected for their advanced material properties. SiC offers superior oxidation resistance and high-temperature stability, outperforming zirconium under accident conditions, while UN fuel provides better thermal conductivity and a higher melting point than , enhancing heat removal. As ATF systems must remain compatible with current and future LWR designs, their viability depends largely on performance under standard operating conditions. This study investigates whether the UN–SiC combination can maintain—or potentially enhance—reactor safety and efficiency through improved neutronic behavior. To evaluate this, the neutronic performance of UN–SiC ATF systems was analyzed and compared with that of conventional -Zr design. Key neutronic characteristics, such as the infinite multiplication factor ( ), burnup behavior, neutron flux spectra, inventory, energy deposition, and temperature coefficients of reactivity were examined for different configurations under steady-state typical operating conditions using the Reactor Monte Carlo (RMC) code. According to the results, SiC cladding improves neutron economy by reducing thermal neutron absorption, which slightly increases reactivity and energy deposition uniformity. UN fuel showed sensitivity to content, even though it offered a higher uranium density and better reactivity retention. However, lesser content (e.g., 10%) mitigated the parasitic neutron absorption penalty to an extent. The integrated UN-SiC system demonstrated promising performance, achieving a balance between plutonium breeding and reactivity retention; however, optimizing enrichment is essential for addressing the disadvantages of . In addition, fuel- and moderator-temperature feedback were quantified for the reference and integrated ATF cases. The UN–SiC concepts exhibited noticeably more negative fuel and moderator temperature coefficients than the -Zr baseline, underscoring an inherent safety advantage that complements their neutronic performance. Overall, this study highlights the neutronic advantages of UN–SiC ATF designs under normal operating conditions, demonstrating their potential to improve safety and efficiency within existing reactor frameworks. These findings contribute to developing next-generation nuclear fuels, emphasizing material synergies for advancing light-water reactor resilience and sustainability.
Tayboga et al. (Sun,) studied this question.