The Molten Salt Reactor (MSR) system produces fission power from a molten salt fuel circulating in a fast or epithermal-spectrum reactor and contains an integrated fuel cycle.
In a Molten Salt Reactor (MSR), the fuel is dissolved in a fluoride salt coolant. Prior MSRs were mainly considered as thermal-neutron-spectrum graphite-moderated concepts. Since 2005 R&D has focused on the development of fast-spectrum MSR concepts (MSFR) combining the generic assets of fast neutron reactors (extended resource utilization, waste minimization) to those relating to molten salt fluorides as fluid fuel and coolant (favourable thermal-hydraulic properties, high boiling temperature, optical transparency). In addition, MSFRs exhibit large negative temperature and void reactivity coefficients, a unique safety characteristic not found in solid-fuel fast reactors (Mathieu et al, 2009). MSFR systems have been recognized as a long term alternative to solid-fuelled fast neutron systems with unique potential (negative feedback coefficients, smaller fissile inventory, easy in-service inspection, simplified fuel cycle, etc.).
Apart from MSR systems, other advanced reactor concepts are being studied employing liquid salt technology as primary coolant in Fluoride-cooled High-temperature Reactor (FHR), or intermediate coolant as an alternative to secondary sodium in Sodium Fast Reactors (SFR) and to intermediate helium in Very High Temperature Reactors (VHTR).
More generally speaking, the development of higher temperature salts as coolants could bring new nuclear and non-nuclear applications. These salts could facilitate heat transfer for nuclear hydrogen production concepts, concentrated solar electricity generation, oil refineries and shale oil processing facilities amongst other applications (Forsberg et al., 2007).
Fluoride-cooled High-temperature Reactors (FHRs) combine the use of liquid fluoride salt coolants (like MSRs), pool type cores and vessel configurations in common with many sodium reactor designs, and coated particle fuels similar to high temperature gas-cooled reactors (Forsberg et al., 2008). The two most developed FHR designs are the 1200 MWe Advanced High Temperature Reactor (AHTR) that employs prismatic fuel elements and the 410MWe Pebble Bed Advanced High Temperature Reactor (PB-AHTR). The better fluoride salt heat transport characteristics, as compared to helium, enable power densities 4 to 8 times greater as well as power levels over 4000 MWt with passive safety systems. Fuel cycle characteristics are essentially identical to those of the VHTR, while intermediate heat transport, power conversion and balance of plant are essentially identical to those of the “reference” MSR.
Advantages and challenges
The renewal and diversification of interests in molten salts led the MSR PSSC in 2008 to shift the R&D aims and objectives promoted in the original Generation IV Roadmap, issued in 2002, in order to include in a consistent body the different applications then envisioned for fuel and coolant salts.
Since then, two baseline concepts are considered which have large commonalities in basic R&D areas, particularly for liquid salt technology and materials behaviour (mechanical integrity, corrosion). These are:
In addition, opportunities offered by liquid salts for intermediate heat transport in other systems (SFR, LFR, VHTR) are investigated. Liquid salts offer two potential advantages: smaller equipment size, because of the higher volumetric heat capacity of the salts, and the absence of chemical exothermal reactions between the reactor, intermediate loop and power cycle coolants.
Liquid salt chemistry plays a major role in the viability demonstration, with such essential R&D issues as: the physico-chemical behaviour of coolant and fuel salts, including fission products and tritium; the compatibility of salts with structural materials for fuel and coolant circuits, as well as fuel processing material development; the on-site fuel processing; the maintenance, instrumentation and control of liquid salt chemistry (redox, purification, homogeneity), and; safety aspects, including interaction of liquid salts with various elements.
GIF progress in 2009
Significant progress was achieved in 2009. This included:
A general discussion on these topics can be found in the Generation IV International Forum 2009 Annual Report (pages 52-59). More detailed explanations can be found in the bibliography below.
Recent MSR research papers
Auger T., Cury R., Chevalier J.P. (2009), Development of Ni-W-Cr alloys for Gen IV Nuclear Reactor Applications, TMS annual meeting, 15-19 February 2009, San-Francisco, USA.
Beneš O., et al., (2008), Review Report on Liquid Salts for Various Applications, Deliverable D50, Assessment of Liquid Salts for Innovative Applications, ALISIA project, of the 7th Euratom Framework Programme.
Beneš O., Konings R.J.M., Actinide Burner Fuel: Potential compositions based on the thermodynamic evaluation of the MFX-PuF3 (M=Li, Na, K, Rb, Cs, La) system. J. Nucl. Mater. 377 (2008) 449.
Beneš O., Konings R.J.M., Thermodynamic evaluation of the LiF-NaF-BeF2-PuF3 system, J. Chem. Thermodyn., 41 (2009) 1086-1095.
Delpech S., et al., (2008a), Optimization of fuel reprocessing scheme for innovative molten salt reactor, paper presented at the October 2008 Molten Salts Joint Symposium, Kobe, Japan.
Delpech S., et al., (2008b), Actinides/Lanthanides Separation for the Thorium Molten Salt Reactor Fuel Treatment, paper presented at ATALANTE 2008, Montpellier, France.
Delpech S., et al., (2009a), Reactor Physics and Processing Scheme for Innovative Molten Salt Reactor System, J. of Fluorine Chemistry, 130, Issue 1, p. 11-17.
Delpech S., et al., (2009b), MSFR: Material issues and the Effect of Chemistry Control, 2009 GIF Symposium Paris France (2009).
Fabre S., et al., (2009), Corrosion of metallic materials for molten salt reactors, Proceedings of ICAPP’09, May 10-14 2009, Paper 9309, Tokyo, Japan.
Forsberg C.W., et al., (2007), Liquid Salt Applications and Molten Salt Reactors, presented at ICAPP, 13-18 May 2007, Nice, France.
Forsberg C.W., et al., (2008), Design Options for the Advanced High-Temperature Reactor, Paper presented at ICAPP, 8-12 June 2008, Anaheim, CA, United States.
Holcomb D.E., et al., (2009), An Analysis of Testing Requirements for Fluoride Salt-Cooled High Temperature Reactor Components, ORNL/TM-2009/297, November 2009.
Hoogmoed M.W., (2009), A Coupled Calculation Code System for the Thorium Molten Salt Rector, MSc. Thesis, PNR-131-2009-009, Delft, Netherlands.
Hron M., et al., (2008), Design Reactor Physical Program in the Frame of the MSR-SPHINX Transmuter Concept Development, paper presented at ICAPP, 8-12 June 2008, Anaheim, CA, United States.
Ignatiev V., et al., (2008a), Compatibility of selected Ni-based alloys in molten Li,Na,Be/F salts with PuF3 and tellurium additions, Nuclear Technology, Vol. 164, N°1, pp.130-142, October 2008.
Ignatiev V., et al., (2008b), Main Results of IAEA CRP on Studies of Advanced Options for Effective Incineration of Radioactive Waste: Case for Molten Salt Transmuter Systems, Paper presented at the 10th Information Exchange Meeting on Actinide and Fission Product Partitioning & Transmutation, 6-10 October 2008, Mito, Japan.
Mathieu L., et al., (2009), Possible Configurations for the TMSR and advantages of the Fast Non Moderated Version, Nuclear Science and Engineering 161, pp. 78-89.
Merle-Lucotte E., et al., (2009a), Minimizing the fissile inventory of the molten salt fast reactor, Proceedings of the International Conference Advances in Nuclear Fuel Management IV (ANFM IV), April 2009, Hilton Head Island, USA.
Merle-Lucotte E., et al., (2009b), Optimizing the Burning Efficiency and the Deployment Capacities of the Molten Salt Fast Reactor, Proceedings of the International Conference Global 2009 - The Nuclear Fuel Cycle: Sustainable Options & Industrial Perspectives, September 2009, Paris, France.
Nagy K., et al., (2008), Parametric studies on the fuel salt composition in thermal molten salt breeder reactors, Proceeding of PHYSOR 2008 International Conference, Interlaken, Switzerland, paper 277.
Nagy K., et al., (2010), Definition of breeding gain for molten salt reactors, Proceeding of PHYSOR 2010 International Conference, Pittsburg, USA, to be published.
Renault C., et al., (2009), The Molten Salt Reactor (MSR) in Generation IV - Overview and Perspectives, 2009 GIF Symposium Paris, France (2009).
Salanne M., et al., (2009), Transport in molten LiF-NaF-ZrF4 mixtures: a combined computational and experimental approach, Journal of Fluorine Chemistry, 130, pp. 61-66.
Zherebtsov A., et al., (2008), Experimental Study of Molten Salt Technology for Safe, Low-Waste and Proliferation Resistant Treatment of RadioactiveWaste and Plutonium in Accelerator Driven and Critical Systems, ISTC-1606 Project, Final Report, International Scientific Centre, Moscow, Russian Federation.
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