Generation 4 IMSR Fission Technology, A Perfect Fit for Repowering Coal

By Simon Irish

Despite the world’s growing awareness of the scale of climate change and the immense challenge of mitigating it, coal is still a predominant source of power, comprising 27 percent of total global primary energy consumption in 2021, according to the BP Statistical Review of World Energy.

With its roughly 900 grams of CO2-equivalent per kilowatt-hour (gCO2/kWh) life cycle emissions, it is one of the most emissions-intensive forms of electricity generation. This may leave some asking:

Why don’t we simply shut down all the coal plants and replace them all with clean energy?

Generation IV fission technologies offer a commercially realistic chance of achieving that for the first time, allowing coal plants to be repurposed as clean energy sources with comparable electricity output but without carbon emissions or other pollution.

Numerous coal plants have already been repurposed for natural gas or biomass combustion. However, natural gas is still a heavy CO2 emitter with volatile pricing and biomass’ land use is simply not sustainable enough to progress beyond a minor net contribution.

Generation IV fission reactors, such as Terrestrial Energy’s Integral Molten Salt Reactor (IMSR), operate at the temperature of a coal boiler and are a feasible and highly scalable way to substitute coal combustion for power generation while being cost competitive and capital efficient. This is so much more preferable to decommissioning and dismantling coal plants mid-life and starting from scratch.

When coal plants are decommissioned, there are economic and social impacts that reverberate throughout the communities and regions where those plants operated. Jobs are lost, and tax revenues decline. The contribution by coal plants to the tax base is often essential to education and other community services. Alternative sources of power may not materialize for many years, or possibly ever. No community wants to face these types of losses.

However, some places in North America are recognizing that Generation IV fission technology offers a solution for a just transition. Here is how.

Coal-fired electric power plants consist of three major components:

  • The coal-fired boiler – the part that heats water generating high temperature (~580 degrees C) and pressure steam
  • The steam turbine and electric generator – the part that converts thermal energy into electricity
  • The transmission infrastructure – the part that distributes that electricity into the grid.

The polluting part of the plant is the coal-fired boiler. The rest is non-emitting. If we substitute the boiler with a non-emitting energy source, we could enlist the rest of the power plant for many more years of profitable use. The workforce is retained, as is the grid supply. Tax revenues continue. Reliable, low-cost electricity continues to flow. Community upheaval is avoided.

In 2021, the United Nations Economic Commission for Europe (UNECE) published a study on life-cycle GHG emissions. This study compared all major energy sources and their respective life-cycle emissions. Nuclear energy was shown to be the lowest life-cycle emitter of GHGs of all energy sources, at 5.1 to 6.4 grams of CO2/kWh. It was also shown to have the lowest land use of all power generating sources, as well as lowest materials use per unit of energy for the highest sustainability score. This is corroborated by the IPCC and the World Bank.

The IPCC life-cycle emissions study from 2014 estimated the median life-cycle emissions of nuclear at 10 grams of CO2/kWh – again, among the very lowest of all energy sources. Regarding sustainability, the World Bank published a 2017 paper on “The Growing Role of Minerals and Metals for a Low Carbon Future” concluding that “[t]he report clearly shows that the technologies assumed to populate the clean energy shift—wind, solar, hydrogen, and electricity systems—are in fact significantly MORE [World Bank emphasis] material-intensive in their composition than current traditional fossil-fuel-based energy supply systems.”

Repowering existing coal plants with the Generation IV IMSR is likely to be the least minerals and metals intensive pathway

Led by West Virginia, a few states have recently proposed or passed legislation specifically rescinding moratoria on the construction of nuclear power plants. States such as Indiana, Illinois, Montana, and Wyoming are weighing similar legislation. The common feature of many of these states is that they have a strong historic dependency on coal and coal-fired electric generation.

Nuclear technology is a possible solution to their coal dependency. However, not any nuclear technology will suffice. Only certain Generation IV fission technologies with unique high-temperature operation provide for that opportunity.  If the idea is to replace the coal-fired boiler with heat from a co-located nuclear reactor, that nuclear reactor must have the following characteristics:

  • It must be scalable and available at a competitive cost without a requirement of continuous government subsidy.
  • It must have the high-temperature output to match the requirement of the coal plant’s steam supply and power conversion equipment, and the IMSR Plant’s use of molten salt fission technology (a Generation IV technology) can achieve this.
  • It must replace the coal-fired boiler using non-nuclear grade systems to be a feasible project in a carefully regulated nuclear sector.

The conventional Generation III nuclear power plant technologies – which are water-cooled water-moderated fission technologies – cannot meet the above criteria. Other Generation IV technologies either cannot match a coal plant’s steam temperatures or have proven costly to deploy. They may also pose supply chain challenges, notably with fuel.

Terrestrial Energy’s IMSR employs molten salt reactor technology. Its low pressure and high temperature operation and use of standard assay Low Enriched Uranium fuel are unique. Those technology and design choices deliver a simplified safety case. This offers transformational nuclear cost advantages, and these are needed for nuclear energy to move out from under the coattails of government and achieve broad market deployment.

The IMSR features an isolating molten salt loop of simple nitrate salts to transfer heat from the nuclear systems to a separated facility that houses the steam supply and power generation systems. That nitrate salt – termed solar salt – can also transport high-temperature (~585 degrees C) thermal energy for general industrial use. This dual use potential is termed “cogeneration.”

Hence, IMSR technology and the IMSR cogeneration plant design hold the potential to repurpose coal plants. This combination makes efficient use of much of the plant’s existing infrastructure and keeps millions of dollars’ worth of capital in continued productive use and with that jobs for hundreds of local workers.

Besides states passing or proposing new pro-nuclear development legislation, other government and industry agencies have endorsed this plan. The director of the U.S. Department of Energy Loan Programs Office (LPO), Jigar Shah, has voiced support for the coal-to-nuclear transition, and he is seeking to put the strength of his office’s resources behind that support. The LPO has an $11 billion carve-out specifically for SMRs (out of a total $40 Billion).

In March 2022, UK energy consultancy TerraPraxis released a report describing a program to standardize the design and deployment for replacement of heat sources at coal plants with high-temperature SMRs. This “Repowering Coal” program has been developed by a coalition including Microsoft, Massachusetts Institute of Technology (MIT), Southern Company, Tennessee Valley Authority, and other large electric utility companies, among others.

The feasibility of repowering mid-life coal plants with IMSR Generation IV fission technology requires a closer look, considering 2 Terawatts of coal capacity either already decommissioned or slated for decommissioning by 2050, according to the TerraPraxis report. That would require 5,000 IMSR Plants. The transition from dirty coal to clean nuclear represents an extraordinary opportunity to contribute to net-zero emissions by 2050 in a way that protects valuable jobs, tax revenue, and energy security.

No wonder it is getting attention.


United Kingdom