Molten Salt Reactor
The Molten salt reactor (MSR) uses a fuel with naturally low fissile content, which reduces proliferation concerns and many waste management issues as it is able to process dangerous actinides in the reactor.
The fuel used in a MSR consists of a liquid mixture of sodium, zirconium, and uranium fluorides, and is often associated with the use of thorium fuel cycles, potentially a more long-term and sustainable fuel source.
The benefits of using a liquid fuel are the easy inclusion of plutonium and actinides which avoids the need fuel fabrication. The system produces fission power from the circulation of molten salt fuel in a fast or epithermal-spectrum reactor, meaning that the reactor will only produce energy when a critical mass is reached inside the reactor.
The fuel flows through graphite core channels, generating heat that is transferred to a secondary coolant system through an intermediate heat exchanger and then to the power conversion system through another heat exchanger.
Compared with solid-fuelled reactors, MSR systems have lower fissile inventories, no radiation damage constraint on fuel burn-up, no spent nuclear fuel, no requirement to fabricate and handle solid fuel, and a homogeneous isotopic composition of fuel in the reactor.
There are currently no system arrangements signed for the MSR, and given its R&D needs for system development, it is estimated to be deployable by 2025
MSRs were first developed in the late 1940s and 1950s for aircraft propulsion. In addition, the United States developed an 8 MWth Molten Salt Reactor Experiment, which operated for about four years, successfully demonstrating the reactor system. However, the political impetus at the time was for plutonium-based reactors and so this experiment was shut down.
Because of their low fissile content, MSR’s have higher inherent safety features and fewer technical obstacles, as they do not have to deal with highly damaging fast neutrons in the design. Waste produced is minimal and of much shorter half-life than that of fuel that does not process actinides within the reactor.
Furthermore, it is extremely easily adapted to a thorium cycle, which many see as a key benefit. In addition, liquid salts offer 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.