Stable salt reactor

The stable salt reactor (SSR) is a nuclear reactor design under development by Moltex Energy Canada Inc. and its subsidiary Moltex Energy USA LLC, based in Canada, the United States, and the United Kingdom, as well as MoltexFLEX Ltd., based in the United Kingdom.

The SSR design being developed by Moltex Energy Canada Inc. is the Stable Salt Reactor - Wasteburner (SSR-W), which incorporates elements of the molten salt reactor, and aims to have improved safety characteristics (intrinsically safe) and economics (LCOE of $45/MWh USD or less) over traditional light water reactors.

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. Additionally, the modular design would allow factory production of components and delivery to site by standard road transportation, reducing costs and construction timescales.

The fuel design is a hybrid between light water reactor fuel assemblies and traditional molten salt reactor approaches, in which the fuel is mixed with the coolant. The liquid salt fuel mixture is contained within fuel assemblies that are very similar to current light water reactor technology. The fuel assemblies are then submerged in a pool of liquid salt coolant.

Moltex Energy Canada Inc. plans to deploy the SSR-W and associated waste recycling facility in New Brunswick, Canada in partnership with NB Power. The company has support and funding from the Canadian federal government, the government of New Brunswick, NB Power, Ontario Power Generation, ARPA-E, IDOM, SNC Lavalin.

The basic unit of the reactor core is the fuel assembly. In the SSR-W, each assembly contains nearly 300 fuel tubes of 10 mm diameter, filled to a height of 1.8 m with fuel salt. The tubes have “diving bell” gas vents at the top to allow fission gases to escape. The assemblies are loaded vertically into the core, with fresh assemblies entering through an airlock and inserted into the core through a fuelling machine.

The fuel in the SSR is two-thirds sodium chloride (table salt) and one-third mixed lanthanide/actinide trichlorides. Fuel for the initial reactors is planned to come from converted spent nuclear fuel from existing conventional reactors. 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. Since the reactor operates in the fast spectrum, the tubes will be exposed to very high neutron flux and so will suffer high levels of radiation damage estimated at 100–200 dpa over the tube life. The highly neutron damage tolerant steel, PE16 will therefore be used for the tubes. Other steels with fast-neutron tolerance (such as T9, NF616 and 15-15Ti) could also be used depending on the local supply chain capabilities.