The Molten Salt Reactor (MSR) in Generation IV - Overview and perspectives

In a Molten Salt Reactor (MSR), the fuel is dissolved in a fluoride salt liquid mixture also playing the role of primary coolant. MSRs have very specific characteristics that may enable this system to have unique capabilities and competitive economics for actinide burning and extending fuel resources. MSR concepts have been investigated by ORNL (USA) in the 60's and 70's. A favorable feedback experience was gained from the successful operation of the MSRE (8 MWth) between 1965-69. A reference breeder design 1000 MWe with a thermal spectrum and thorium fuel cycle (MSBR) was then proposed and intensively analyzed. However, the premature termination of the program in 1975 left a number of open questions relative to the viability of the concept. Prior MSRs were mainly considered as thermal-neutron-spectrum graphite-moderated concepts. This is an essential outcome of the European R&D that the interest has been focused on fast spectrum concepts (MSFR), without graphite in the core, which have been recognized as long term alternatives to solid-fuelled fast neutron reactors with attractive features (very negative feedback coefficients, smaller fissile inventory, easy in-seivice inspection, simplified fuel cycle.. .). MSFR designs are available for breeding and for minor actinide burning. They are robust reference configurations (with significant improvement compared to MSBR), allowing to concentrate R&D on the remaining critical areas (determination of liquid salt properties of reference compositions, definition and assessment of the fuel salt clean-up scheme, and qualification of high performance materials). In USA, the main interest is placed on liquid salts as a primary coolant for the Advanced High Temperature Reactor (AHTR). The AHTR is a high temperature reactor with higher power density than the VHTR and passive safety potential from small to veiy high unit power (> 2400 MWt). A Pebble Bed Advanced High Temperature Reactor (PB-AHTR), using coated particle fuel embedded within a graphitic matrix cooled by liquid fluoride salt and operating at -900 MWt is the most actively developing commercial scale plant design. A research, development and demonstration roadmap is under study for component testing to support aPB-AHTR prototype scale plant and a development path for the structural materials is being established. Europe (EURATOM), France and USA participate in the Generation IV MSR Steering Committee. Although the European and USA interests are focused on different baseline concepts (MSFR and AHTR, respectively), large commonalities in basic R&D areas (liquid salt technology, materials) exist and the Generation IV framework plays an important role to optimize the R&D effort at the international level.JRC.E.3-Materials researc