The Molten Salt Reactor (MSR) system produces fission power fom a molten salt fuel circulating in a fast or epithermal-spectrum reactor and contains an integrated fuel cycle.

In the MSR system, the fuel is a circulating liquid of sodium, zirconium, and uranium fluorides. The molten salt fuel flows through graphite core channels, producing an epithermal spectrum. The heat generated in the molten salt is transferred to a secondary coolant system through an intermediate heat exchanger, and then through a tertiary heat exchanger to the power conversion system. The reference plant has a power level of up to 1,000 MWe. The system has a coolant outlet temperature of 700 degrees Celsius, possibly ranging up to 800 degrees Celsius, affording improved thermal efficiency.

The closed fuel cycle can be tailored to the efficient burn up of plutonium and minor actinides. The MSR's liquid fuel allows addition of actinides such as plutonium and avoids the need for fuel fabrication. Actinides - and most fission products - form fluorinides in the liquid coolant. Molten fluoride salts have excellent heat transfer characteristics and a very low vapor pressure, which reduce stresses on the vessel and piping.

This diagram illustrates a schematic concept of the reactor system and does not represent the reference design.

Diagram source: http://www.ne.doe.gov/genIV/documents/gen_iv_roadmap.pdf

Advantages and challenges

Molten salt reactor systems use liquid salts as a coolant and a fuel together. The main benefits of the MSR system are that it offers an integrated fuel cycle, embodying a burner/breeder reactor concept whilst taking advantage of the excellent heat transport properties of molten salt. These properties imply that the building housing a MSR could be smaller than for other reactor concepts under development and that the thermal power output would be higher. A number of other promising applications for molten salts beyond the MSR itself have been identified. These use a variety of salt compositors that vary according to the envisioned application. These include: liquid fuel; primary or secondary coolant; and pyrochemistry solvent. Molten salts might also be used as a substitute for primary or secondary circuit working fluids in the SFR and VHTR. The molten salt chemistry and handling, with the resulting corrosion of reactor components, along with the development of materials and the fuel cycle, are the main challenges for the development of this system.

GIF progress in 2007

It is planned to complete the draft system research plan for the MSR shortly. As part of the overall roadmap for the system's development, a scoping and screening phase will continue until 2011. At that point, confirmation of the potential of salt (selection, properties and compatibility with other materials) will have been established. The selection of reference designs will be made by 2018, at which point the project will move into the performance phase.

Recent MSR research papers

Mitachi, K., Yamamoto, T. & Yoshioka, R. (2007) Three-Region Core Design for 200-MW(electric) Molten-Salt Reactor with Thorium-Uranium Fuel, Nuclear Technology: 158(3): 348-357.

Hron, M.J. et al (2007), MSR – SPHINX concept program EROS (Experimental zeRO power Salt reactor SR-0). The proposed experimental program as a basis for validation of reactor physics methods, 2007 International Congress on Advances in Nuclear Power Plants (ICAPP '07).

Lecarpentier, D. (2006) Contribution aux travaux sur la transmutation des déchets nucléaires, voie des réacteurs a sel fondu : le concept amster, aspect physique et sûreté  (Contribution to the work on radioactive waste transmutation, molten salt reactors : The Amster concept, physical aspects and safety), Doctoral dissertation, Conservatoire national des arts et métiers, Paris.

Mathieu et al (2006), The thorium molten salt reactor: Moving on from the MSBR, Progress in Nuclear Energy: 48(7): 664-679.

Forsberg, C. & Peterson, P. (2004), An Advanced Molten Salt Reactor Using High-Temperature Reactor Technology, 2004 International Congress on Advances in Nuclear Power Plants (ICAPP'04).

Forsberg, C. (2004) Molten Salt Reactor Technology Gaps, 2004 International Congress on Advances in Nuclear Power Plants (ICAPP'04).

Ignatiev, V., Feynberg, O., Mjasnikov, A., Zakirov, R. (2003), Reactor physics and fuel cycle analysis of a molten salt advanced reactor transmuter, 2003 International Congress on Advances in Nuclear Power Plants (ICAPP ’03).

MacPherson, H.G. (1985) The Molten Salt Reactor Adventure, Nuclear Science and Engineering 90: 374-380.

Related links

DOE Nuclear Energy Research Initiative MSR Program Plan (pdf, 572 kb).

E-mail contact: msr@gen-4.org

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