Molten Salt Reactors are characterized by the use of molten salt as coolant (Molten-salt-cooled solid-fuel reactors as FHR) and both as fuel and coolant (circulating fuel reactors as MSFR). Especially for the latter case, the use of molten fluoride or chloride salt leads to peculiar characteristics that are not present in conventional reactors, such as the drift of the delayed neutron precursors, the strong coupling between neutronics and thermal-hydraulics, and the internal heat generation in the fluid.
MSFR – Molten Salt Fast Reactor
The Molten Salt Fast Reactor (MSFR) is a fast-spectrum, circulating fuel molten salt reactor.
The reference MSFR is a 3000 MWth reactor with a total fuel salt volume of 18 m3, operated at a mean fuel temperature of 700°C. The fuel circuit is made by the core cavity and the recirculation loops including the inlet and outlet pipes, a gas injection system, salt-bubble separators, pumps and fuel heat exchangers. 16 cooling sectors are arranged circumferentially around the vessel. Due to the liquid nature of the nuclear fuel, which does not require the presence of any solid fuel-element, and the fast neutron spectrum which does not require any moderating materials, the MSFR core is constituted by a simple, empty cavity, surrounded by an axial reflector and a radial blanket. The fuel salt, with an inlet temperature of about 650 °C, enters radially from the bottom into the active zone and its heated to the outlet temperature of about 750 °C. The fuel then exits from the top of the core and it is recirculated through the 16 fuel sectors. In addition, the current design of the MSFR foresees an on-line bubbling system for removing both the gaseous fission products via dilution and the metallic particles via capillary sticking.