How it works


The IMSR Plant uses molten salt fission technology. This is high-temperature fission technology, classified as Generation IV fission technology class under international treaty.

“Generation IV designs will use fuel more efficiently, reduce waste production, be economically competitive, and meet stringent standards of safety and proliferation resistance…” according to the Generation IV International Forum charter signed in 2001 by US, Canada, UK, and others.

Advanced Nuclear Facility Plant Rendering

The IMSR plant.


Molten salt fission technology uses a molten salt as coolant and fuel. Conventional fission technology uses a water coolant circulating through a highly pressurized system to cool solid fuel elements, which are the signature technology features of current nuclear power plants.

A nuclear reactor requires a high-performance coolant for safe and efficient commercial operation. Molten salts are such coolants. They have exceptional thermal stability, making them superior reactor coolants compared to water. This permits safe high-temperature and low-pressure reactor operation, which is crucial for heat supply to the industry, to reduce the cost of nuclear energy, and transform the efficiency of nuclear electric power generation.

Graphical Background


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. This is important to safety, social license, and commercial performance as well.

The IMSR improves upon earlier molten salt reactor designs by incorporating key innovations that create a reactor suitable for commercial industrial use and ready for near-term deployment. The IMSR cogeneration plant design incorporates many aspects of molten salt reactor operation researched, demonstrated and prototyped by test reactors at the Oak Ridge National Laboratory.


Operating at 44% thermal efficiency (net), an IMSR cogeneration plant can generate 392 megawatts of electricity from 884 megawatt of thermal reactor power. Heat at 700°C is generated from two thermal-spectrum, graphite-moderated, molten-fluoride-salt reactors (IMSR).

These reactors 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 Replaceable IMSR Core-unit

The key challenge to molten salt reactor commercialization has been graphite’s known lifetime limitations 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 on a regular basis would add undesirable complexity and cost 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 IMSR Core-unit supports high-capacity factors of IMSR power plants and hence high capital efficiency. Its 7-year operating period 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.