Stable salt reactor
SSRs, which are protected by robust patents, are being designed so that they will not need expensive containment structures and components to mitigate radioactive releases in accident scenarios.
The design would preclude the type of widespread radiological contamination that occurred in the Chernobyl or Fukushima accidents, because any hazardous isotopes that might otherwise become airborne would be chemically bound to the coolant.
[2] Additionally, the modular design would allow factory production of components and delivery to site by standard road transportation, reducing costs and construction timescales.
In the UK, the fuel could come from the stocks of civil plutonium dioxide from PUREX downblended and converted to chloride impurities added to reduce any proliferation concerns.
Trichlorides are more thermodynamically stable than the corresponding fluoride salts, and can therefore be maintained in a strongly reducing state by contact with sacrificial nuclear-grade zirconium metal added as a coating on, or an insert within, the fuel tube of the SSR-W. As a result, using this patented approach, the fuel tube can be made from standard nuclear certified steel without risk of corrosion.
The coolant also contains an agent to reduce its redox potential, making it virtually non-corrosive to standard types of steel.
This is made possible by the combination of a high negative temperature coefficient of reactivity and the ability to continually extract heat from the fuel tubes.
For the SSR-W, diverse and redundant safety is also provided by an array of gravitationally driven boron carbide control rods.
[12] Use of molten salt fuel with the appropriate chemistry eliminates the hazardous volatile iodine and caesium, making multi-layered containment unnecessary to prevent airborne radioactive plumes in severe accident scenarios.
For the SSR-W, the noble gases xenon and krypton would leave the reactor core in normal operation, but would be trapped until their radioactive isotopes decay, so there would be very little that could be released in an accident.
[2] In a water-cooled reactor, high internal pressures provide a driving force for dispersion of radioactive materials in the event of an accident.
Physical separation of the steam-generating system from the radioactive core, by means of a secondary coolant loop, eliminates high pressure within the reactor.
Immediately after a nuclear reactor shuts down, almost 7% of its previous operating power continues to be generated, from the decay of short half-life fission products.
In the event of a reactor shutdown and failure of all active heat-removal systems in the SSR, decay heat from the core would dissipate into air-cooling ducts around the perimeter of the tank that operate continually.
Today’s reactors that are fuelled by reprocessed spent fuel need very high-purity plutonium to form a stable pellet.
A 2016 report by the Canadian Nuclear Laboratories on recycling of CANDU fuel estimates that pyroprocessing would cost about half as much as more conventional reprocessing.
With this range of reactor options and the large global reserves of uranium and thorium available, SSRs could fuel the planet for several thousands of years.
[15] Given the pre-commercial nature of the technology, the figures for capital cost and LCOE are estimates, and may increase or decrease during completion of the development and licensing processes.
