Neutron Economy and the Thorium Fuel Cycle in Thorium Molten Salt Reactors: A Systematic Review

This study investigates neutron economy and the thorium fuel cycle within Thorium Molten Salt Reactors to evaluate their potential for sustainable nuclear energy production. Using a Systematic Literature Review (SLR) methodology, this study synthesized recent research published between 2020 and 2026, while also using selected foundational sources from 1960 onward for core nuclear-theory parameters. Data were analyzed using a qualitative and comparative approach, focusing on thorium-232 conversion pathways, uranium-233 production mechanisms, and neutronic performance parameters. The findings indicate that U-233 is a superior fissile fuel for the thorium cycle, exhibiting a high neutron reproduction factor of 2.28 for thermal neutrons and 2.50 for fast neutrons, which supports efficient fuel breeding. The thorium cycle offers significant environmental and security benefits, including a substantial reduction in long-lived transuranic actinides and enhanced proliferation resistance due to the presence of uranium-232, which emits high-energy gamma radiation. Furthermore, TMSR technology provides inherent safety through a negative temperature coefficient and the ability for online fuel processing to remove gaseous fission products.
Unlike previous review studies, this research integrates neutron economy, U-233 purity, breeding ratio, salt chemistry, and reactor safety into a unified conceptual framework, providing a comprehensive analytical perspective for the evaluation of thorium molten salt reactors. The study concludes that while the thorium-uranium cycle is a highly effective alternative for improving neutron efficiency and long-term sustainability, successful commercial deployment depends on achieving U-233 purity levels of approximately 85%. Additionally, further research is required to address remaining challenges in structural materials, salt redox chemistry control, and fuel reprocessing.