How it Works
Molten salts are thermally very stable, making them superior coolants compared to water. This permits lower pressure and high temperature operation. Both are crucial to reducing cost, substantially improving efficiency of electric power generation. IMSR® high-temperature operation delivers a much broader use-case for fission energy in industry.
When a molten salt coolant and molten salt fuel are used in combination, the reactor has the potential to incorporate the powerful virtues of passive and inherent reactor safety as well. As a result, using molten salt technology in the IMSR® plant that is “walk-away” safe delivers transformative safety and commercial advantages.
Operating at greater than 44 percent thermal efficiency (net), an IMSR® plant can generate 400 megawatts of electricity. Thermal energy is generated from two thermal-spectrum, graphite-moderated, molten-fluoride-salt reactor systems. These use today’s standard nuclear fuel – comprising standard-assay low-enriched uranium (less than 5 percent U-235) – critical for near-term commercial deployment of IMSR® plants. The IMSR® plant design incorporates many aspects of Molten Salt Reactor operation that were researched, demonstrated and prototyped by test reactors at the Oak Ridge National Laboratory.
The Replaceable IMSR® Core-unit
The IMSR® improves upon earlier Molten Salt Reactor designs by incorporating key innovations that create a reactor suitable for industrial commercial use and ready for near-term deployment.
The key challenge to MSR commercialisation has been graphite’s limited lifetime in a reactor core. Commercial reactors require high-energy densities in the reactor core to be economic, but such high-power densities significantly reduce the graphite moderator’s lifespan. Replacing the graphite moderator is difficult to do safely and economically in a commercial setting.
The IMSR® patented innovation solves this problem by integrating the primary reactor components, including the graphite moderator, into a sealed and replaceable reactor core – called the “IMSR® Core-unit.” This has an operating lifetime of seven years, and it is simple and safe to replace.
The Core-unit supports high-capacity factors of IMSR® power plants and hence high capital efficiency. It also ensures that the materials’ lifetime requirements of other reactor core components are met, a challenge often cited as an impediment to immediate commercialisation of MSRs.
The result is a nuclear plant that delivers a combination of high safety, high energy output, simplicity of operation, versatility and cost-competitiveness necessary for broad and near-term commercial deployment.
For all these reasons, IMSR® plants are a carbon-free alternative to fossil fuel combustion.