Molten Salt Reactor (MSR)

Molten salt reactors (MSRs) use molten fluoride salts as primary coolant, at low pressure. Extending the concept to dissolving the fissile and fertile fuel in the salt. MSRs may operate with a variety of fuels. Much of the interest today in reviving the MSR concept relates to using thorium where an initial source of fissile material such as plutonium-239 needs to be provided. There are a number of different MSR design concepts, and a number of interesting challenges in the commercialisation of many, especially with thorium.

The salts concerned as primary coolant, mostly lithium-beryllium fluoride and lithium fluoride, remain liquid without pressurization from about 500°C up to about 1400°C, in marked contrast to a Pressurized Water Reactor (PWR) which operates at about 315°C under 150 atmospheres pressure.

The main MSR concept is to have the fuel dissolved in the coolant as fuel salt, and ultimately to reprocess that online. Thorium, uranium, and plutonium all form suitable fluoride salts that readily dissolve in the LiF-BeF₂ (FLiBe) mixture, and thorium and uranium can be easily separated from one another in fluoride form. Batch reprocessing is likely in the short term, and fuel life is quoted at 4-7 years, with high burn-up. Graphite as moderator is chemically compatible with the fluoride salts.