Driving change with IMSR

5 December 2018

Terrestrial Energy’s integral molten salt reactor is redefining what a nuclear plant can do. Simon Irish and David LeBlanc explain.

AT TERRESTRIAL ENERGY, WE BELIEVE our integral molten salt reactor (IMSR) can vastly expand nuclear energy’s capabilities. And because it is smaller, more economical and faster to build than traditional reactors, the Generation-4 IMSR power plant opens new markets.

The IMSR is designed to load-follow and pairs well with wind and solar. In addition, the IMSR can generate heat and power that is cost-competitive with fossil fuels.

Inexpensive heat is a real game-changer in reducing carbon emissions. The IMSR is designed to produce 400MWt (190MWe), and IMSR power plants operate at high temperatures (600°C) and are 50% more efficient than traditional reactors. Industrial heat is a huge market, representing two-thirds of industrial energy demand uses, and one-fifth of global energy consumption, according to the International Energy Agency. With the global energy market estimated at over 5 trillion US dollars per year, this is a monumental opportunity.

In addition to producing cost-competitive heat for industrial processes, these plants supply heat for power and synthetic transport fuels production – applications not served at all today by clean energy technologies.

Despite the rapid growth of electric vehicles, over 99% of transport is still powered by fossil fuels. Even with the most aggressive scenario for adopting electric vehicles, there is no evidence that internal combustion engine (ICE) vehicles can be replaced by 2050 with current battery and EV technologies.

But a high-temperature reactor such as the IMSR supports synthetic fuel production for the entire transport sector with zero or negative net emissions. The process:

  • The IMSR produces high-temperature, high-quality heat that is cost-competitive with fossil fuels.
  • This heat powers the decomposition of water to produce hydrogen on a industrial scale, using methods such as high-temperature steam electrolysis or the hybrid sulfur method, a proprietary technology developed by the US Department of Energy (DOE).
  • Carbon is captured from the air or from large single- point industrial sources of carbon dioxide emissions (such as a gas-fired power plant).
  • Well-understood methods of hydrocarbon synthesis combine the hydrogen and carbon into synthetic gasoline, diesel and kerosene.

Producing synthetic fuels with nuclear technology is a route to eliminate emissions from the entire transport sector. When you consider that there are 1.3 billion ICE vehicles, this is a huge carbon mitigation proposition. Advanced reactors, such as the IMSR, are leading candidates for producing clean ‘nuclear’ hydrogen at the scale needed to displace crude oil for transport fuels. Terrestrial Energy USA has partnered with Southern Company and several US Department of Energy (DOE) National Laboratories to examine the efficiency, design and economics for how an IMSR power plant can drive industrial-scale hydrogen using the Hybrid Sulfur method. This carbon-free method of generating hydrogen from water may be more efficient than high-temperature steam electrolysis. With high-quality, cost-competitive heat, the IMSR can also be an economical way to produce hydrogen to power fuel cells in trucks and forklifts, and backup generators for data centres or hospitals.

Building on proven design

Terrestrial Energy has been working to get the IMSR technology to market by the 2020s. The design was the first advanced nuclear plant to successfully complete Phase 1 of the Canadian Nuclear Safety Commission (CNSC) Vendor Design Review, in October 2017, and in October this year it became the first to start Phase 2 of the CNSC review.

The Canadian Nuclear Laboratory (CNL) in Chalk River, Ontario is investigating nuclear innovation as a solution to economic on- and off-grid power generation that is carbon free. Terrestrial Energy has been working since June 2017 on a feasibility study to build an IMSR power plant at the site and we expect to complete this study soon.

Terrestrial Energy USA also is working with Energy Northwest, the Idaho National Laboratory (INL) and others, to explore the possibility of siting an IMSR at the INL site near Idaho Falls.

The IMSR uses a liquid fuel, molten salt reactor system – a fundamentally different design from existing nuclear power plants, which to date have all used solid fuel. The use of a molten salt fuel offers many technical and commercial advantages.

While versatility is important, it is paramount that advanced nuclear technology be cost-competitive with fossil fuels for widespread adoption. An April 2018 report by the Electric Power Research Institute found that if advanced reactors can become cost-comparable with gas-fired generation, they can grab up to 40% of the US market for power generation.

Terrestrial Energy estimates that the IMSR can generate electricity at a full system cost of $50/MWh – competitive with fossil fuels, without producing greenhouse gases.

The IMSR can be built in four years, less than half of the construction time of a conventional nuclear power plant. Terrestrial Energy uses a modular design for ease and speed of construction. Each module is mass-manufactured in a factory, and is easily transportable by truck or rail for on-site modular assembly.

Less than $800 million for construction of an IMSR power plant, the cost is a fraction of the upfront cost of a conventional large reactor. This makes it much easier to finance an IMSR through ordinary means and opens a much wider range of customers.

Because the IMSR power plants are modular, dispatchable and can easily load-follow, they make ideal partners for the variability of wind and solar power, with no carbon dioxide emissions (unlike gas-fired generation) and at grid scale (unlike energy storage for the foreseeable future). As a result, advanced modular reactors such as the IMSR increase grid stability and make grid-level energy storage unnecessary. These advanced reactors can make significant gains in other markets as well.

The IMSR design incorporates many enhancements, but it is based on the demonstrated molten salt reactor (MSR) design developed in the 1960s at the Oak Ridge National Laboratory, and through a series of subsequent programmes at other national laboratories. The Terrestrial Energy design makes full use of the passive safety benefits of MSR.

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 natural mechanisms to dissipate heat from the fission process, which makes it “walk-away safe” to operate.

The IMSR is a thermal-spectrum reactor system that uses a graphite moderator. It operates on a simple fuel cycle and offers high uranium efficiency and low actinide (plutonium) production, compared with conventional power plants.

One of the key challenges to commercialising a MSR is dealing with graphite in the reactor core. Graphite has a limited lifespan when the reactor is operated continuously. Replacing the graphite moderator is difficult to do safely and economically. The IMSR design offers an elegant solution to this problem – integrating the primary reactor components, including the graphite moderator, into a sealed and replaceable reactor core, which has an operating lifetime of seven years, and can be replaced simply and safely. It supports high capacity factors in IMSRs, making them more economical over the long term.

The IMSR design uses standard assay low-enriched uranium fuel with the same level of enrichment (less than 5% U-235) as in conventional nuclear plants use, so fuel is easily available.

Using the standard-assay fuel and replaceable core modules overcomes the thorniest obstacles to commercialising a molten salt reactor design. The IMSR is a revolutionary design but with a clear path to market, and we are making steady progress toward that goal. Our team of engineers is working to deliver the engineering material required for Phase 2 of the CNSC’s Vendor Design Review. We are working closely with regulatory staff in Canada and the USA, so we can move through the process as efficiently as possible.

Meanwhile, Terrestrial Energy has put in place a corporate Industrial Advisory Board, comprising senior executives from North America’s largest nuclear operators, who are providing counsel on the development of the IMSR. With these insights, the Terrestrial Energy team aims to offer a next-generation nuclear power plant that operators truly want to own and operate.  

Supporting IMSR with simulation 


In July, Terrestrial Energy signed a contract with L3 MAPPS for real-time simulation to support the engineering development of the IMSR design, its licensing, and ultimately, operator training.

“We identified modelling and simulation as a priority area last year, so we are delighted now to be working with L3 MAPPS and benefitting from the world-class simulation capabilities that they bring to the IMSR project,” said Simon Irish, chief executive officer of Terrestrial Energy.

The agreement between Terrestrial Energy and L3 MAPPS sets the framework for the companies’ long-term collaboration. 

(Photo: Rangesh Kasturi, president of L3 MAPPS and Terrestrial’s Simon Irish)

Author information: David LeBlanc is Terrestrial Energy’s Chief Technology Officer 

Schematic of the IMSR
How the ISMR works
Total system cost of ISMR

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