Evaluating molten salt reactor technology
Molten salt reactors are nuclear reactors that use a fluid fuel in the form of a very hot fluoride or chloride salt instead of a solid fuel. Since the fuel salt is liquid, it can act both as fuel to produce heat and as coolant to remove and transport it to the power plant. The liquid fuel cannot melt down. The system operates at standard rather than very high pressures, and the fuel is less susceptible to neutron damage, meaning greater use of the fuel. While the original design was conceived in the 1960s, it faced some major drawbacks. The concept has been retained for Gen IV fast-spectrum nuclear systems due to its numerous advantages, with a goal of modifying it to meet new specifications. Scientists initiated the EU-funded project 'Evaluation and viability of liquid fuel fast reactor system' (EVOL) to design the best possible MSFR given physical, chemical and materials studies to prove it satisfies Gen IV goals. EVOL conducted extensive studies to optimise the MSFR design and system configuration using thermohydraulic and neutronic calculations. Unlike previous designs, the blanket salt flows in a circuit that is external to the salt container. This arrangement ensures that neutrons escaping from the reactor core will be captured by the surrounding blanket, thus achieving high neutron economy. Regarding the fissile materials fuelling the MSFR, two salt mixtures containing uranium-235 and plutonium-239 were proposed that meet the reactor's requirements. The focus was on their physicochemical properties, including viscosity, density, melting point, solubility, heat capacity and vaporisation point. Scientists proposed new steps for fuel reprocessing that allow recovering the salt composition. In addition, they evaluated the behaviour of all the fission products in the reprocessing. Part of the effort involved designing a thorium-based reactor that can burn plutonium and minor actinides and then convert them into uranium-233 while minimising production of long-lived waste. Project dissemination activities included 62 publications and 85 presentations at conferences.
Keywords
Molten salt fast reactors, Generation IV, liquid fuel, neutron economy, fuel reprocessing
