How it Works

The IMSR® blends proven molten salt technology with innovative enhancements, including the integration of primary reactor components into a sealed, replaceable vessel

Rendering of the IMSR® Core-unit

The IMSR® uses a fundamentally different reactor technology — a liquid fuel, a molten salt, rather than the solid fuel used exclusively in conventional reactors. This provides a fluid medium to carry a nuclear fuel, a uranium fluoride salt. Molten salts are thermally stable and are excellent heat-transfer fluids, ideal for capturing and dissipating heat from the fission process.

The IMSR® uses simple, safe and natural mechanisms to dissipate heat from the fission process, and this results in a far superior design to reactors that use conventional technology. The use of a molten salt is at the heart of many virtues of the IMSR® and directly leads to IMSR®’s key commercial advantages – a cost-competitive and “walk-away” safe nuclear power plant.

An IMSR® power plant generates 400 megawatts of thermal energy (190 MW electric) with a thermal-spectrum, graphite-moderated, molten-fluoride-salt reactor system. It uses standard-assay low-enriched uranium (less than 5 percent 235U) fuel. It incorporates many aspects of Molten Salt Reactor operation researched, demonstrated and proven by test reactors at the Oak Ridge National Laboratory.

The Replaceable IMSR® Core-unit

The Replaceable IMSR® Core-unit

The IMSR® improves upon earlier Molten Salt Reactor designs by incorporating key innovations that create an industrial reactor ready for commercial deployment.

The key challenge to MSR commercialization was graphite’s limited lifetime in a reactor core. Commercial power reactors require high energy densities in the reactor core to be economical, but such high-power densities significantly reduce the graphite moderator’s lifespan. Replacing the graphite moderator is difficult to do safely and economically.

The distinct IMSR® innovation is an elegant solution to this problem — integrating the primary reactor components, including the graphite moderator, into a sealed and replaceable reactor core. The IMSR® Core-unit, which has an operating lifetime of seven years, is simple and safe to replace. It 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 commercialization of MSRs.

The result is a small modular reactor that delivers a combination of high energy output, simplicity of operation and cost-competitiveness necessary to drive broad commercial deployment.

The IMSR® power plant is the leading new clean energy alternative.