What is it?
Molten salt reactors are a broad range of technologies, in which the molten salt may be used as a combined fuel and coolant – or as a coolant only. The reactor can be designed for energy production or ‘waste burning’ – reducing the content of long-lived radioactive isotopes. Molten salt reactors can operate with different fuels, primarily uranium or thorium, and different salts in different modes – thermal or fast spectrum. In thermal spectrum mode, the neutrons are slowed by a moderator, in a fast spectrum mode, they are not. The speed of the neutrons determines how they interact with elements in the reactor. Advantages include:
- Very flexible designs – big or small
- Some designs can eliminate nuclear waste
- Operating at high temperature for efficient electricity generation, hydrogen production and district heating
- Passive safety:
- As the salt gets hotter it expands and the nuclear reaction slows down
- Some reactors are designed with a ‘freeze plug’. If the temperature rises too high, this transfers the salt into a separate containment vessel
- Reactor designs operate at lower pressures than conventional reactors, meaning there cannot be an explosion due to vessel pressurisation
- Lower operating pressure reduces the need for thick, heavy vessel manufacture, lowering construction cost
- Fissile fuel is intimately mixed with the salt, increasing resistance to proliferation
Further reading
The following references are recommended as starting point to find out more:
What are Molten Salt Reactors (MSRs)? | IAEA Status of Molten Salt Reactor Technology | IAEA Molten Salt Reactors (MSR) | GIF Portal
Links to Blogs, videos etc. can be found on our Media page and we hope to add our own content over time .
Pyrochemical processing
What is Pyrochemical Processing?
In a molten salt reactor, the fuel is mixed with the molten salt, in contrast to existing reactor technologies that use solid fuel. Several sites across the world, e.g. Sellafield in the UK, use aqueous reprocessing to separate out the reusable components of the fuel from the waste. Advanced forms of aqueous reprocessing are being developed. An alternative and complementary option is pyrochemical processing.
A sustainable solution for Net Zero
The molten salt is more robust to high levels of radiation than the organic solvents in aqueous reprocessing making suitable for fuels with higher levels of radiation. In fact, molten salt reactors may operate a pyrochemical process to clean up their salt during operation.
Cleaning up of extraction of unused fuel from conventional reactor fuels and cleaning up of molten salt fuel mean that pyrochemical processing techniques might be used to close the nuclear fuel cycle.
The basics concepts of pyrochemical processing are shown in this video and an example closed fuel cycle is shown below.
Further Reading
Nuclear Energy Agency (NEA) - Pyrochemical Separations in Nuclear Applications
The following provides a more holistic review of reprocessing that puts pyrochemical processing in context against other nuclear fuel recycle capabilities.
Energy storage and transfer
What is it?
Molten salts are commonly used for thermal energy storage. Current applications are in concentrating solar power. Excess heat that is not used for electricity generation is diverted to the molten salt, which is then stored in an insulated tank. After sunset, this thermal energy can be used to produce steam and generate electricity when the sun is no longer providing energy to the plant. This thermal energy storage capacity can also be used to smooth electricity production throughout the day and mitigate the variability associated with solar PV technologies. Molten salts are typically nitrates or carbonates, but there is increased interest in the use of chlorides and more advanced materials. In a nuclear context, since nuclear provides a continuous source of power, molten salt energy storage can be used as a ‘buffer’ between times of peak and low power demand.
