Nuclear, Reactors

Coupling Integral Molten Salt Reactor Technology with Hybrid Nuclear/Renewable Energy Systems

Issue 9 and Volume 121.

By John Kutsch

The Integral Molten Salt Reactor (IMSR) represents a clean energy alternative to fossil fuel combustion for industrial heat and provision, which is compact, efficient, and cost-competitive with fossil fuels. The IMSR is a Gen 4 reactor and a successor of the very effective Molten Salt Reactor Experiment work of Oak Ridge National Lab.

Terrestrial Energy USA is now working with Idaho National Laboratory to couple the IMSR to advanced industrial systems. Several systems have been designed and proposed. These can serve energy-intensive industries with stable heat and power for clean H2, O2 production, and by extension ammonia and methanol production.

Desalination is also a very significant market sector for IMSR heat and power.

IMSR has the potential to be a transformative technology. When coupled with advanced industrial systems, IMSR enables new, transformative clean industries.

An IMSR power plant can rapidly load follow grid power demand. Photo courtesy: Terrestrial Energy USA
An IMSR power plant can rapidly load follow grid power demand. Photo courtesy: Terrestrial Energy USA

How the Integral Molten Salt Reactor Works

  • The term ‘Integral’ refers to the company’s proprietary design in which all the primary components (pumps, moderator and primary HX) of the reactor core are sealed in a compact and replaceable component, the IMSR Core-unit.
  • A new Core-unit is exchanged every 7 years with the old Core-unit stored on site.
  • The IMSR is a “pool-type” reactor with no penetrations into the reactor vessel.
  • IMSR fuel, the Fuel Salt, is a liquid, high-temperature fluoride salt that operates at ~700C.
  • These salts have high thermal stability and are excellent heat transfer liquids.
  • IMSR Fuel salt can be produced today with current methods and within current regulations.
  • The Fuel Salt, which contains the nuclear fuel, never leaves the reactor core vessel during operation.
  • Fuel Salt is circulated in a closed loop up through the graphite core, where the fuel fissions in a thermal neutron spectrum creating heat within the fuel, which then circulates back down through heat exchangers giving up heat to a secondary salt in a primary heat exchanger and isolated loop. The Fuel Salt circulates back into the core.
  • The reactor core contains a graphite moderator – outside of the moderated area, the salt is no longer active.
  • A secondary heat exchanger exchanges heat via secondary salt to a third loop containing a 600C industrial salt that can be transported up to 5 kilometers.
  • The IMSR has a low level of tritium production. Furthermore, the IMSR’s three successive isolation loops further ensures no tritium moves beyond the nuclear island.
  • Uranium enriched to less than 5% is currently intended to fuel the IMSR; however, with future iterations of IMSR technology, the IMSR is very capable of using a diverse array of fuel forms, including thorium-based fuels and spent nuclear fuels from existing nuclear fleets.
  • An IMSR power plant can rapidly load follow grid power demand.
  • An IMSR power plant is anticipated to deliver power at less than $50 per MWh, which is highly competitive with fossil fuel combustion.

This type of high temperature reactor allows for much more than just electricity production. An IMSR power plant can deliver 600C heat by liquid salt up to 5 kilometers to an industrial energy park. This allows the IMSR baseload heat production of nuclear to be switched from electric power provision to the production of the most valuable high energy products in off-peak hours. This maximizes use of IMSR heat energy and allows the IMSR to run in the most capital efficient manner.

All of the primary components (pumps, moderator and primary HX) of the reactor core are sealed in a compact and replaceable component - the IMSR Core-unit. Photo courtesy: Terrestrial Energy USA
All of the primary components (pumps, moderator and primary HX) of the reactor core are sealed in a compact and replaceable component – the IMSR Core-unit. Photo courtesy: Terrestrial Energy USA

The following are examples of process heat applications for IMSR:

Thermal Storage/Desalination

Demands for safe, secure supplies of potable water globally are increasing faster than can be provided by natural, ever-depleting sources of fresh water. Simultaneously, global demand for electricity is also projected to grow significantly.

Desalination of seawater and brackish water is extremely energy intensive. The IMSR is uniquely suited to provide clean, heat energy and electric power on an industrial scale needed at cost-competitive prices to enable far greater deployment of desalination technologies today.

In addition to utilizing heat energy for desalination, hot industrial salts can be directed to a hot salt mass energy storage, a method that is already in use today. These hot salt thermal energy reservoirs supported by IMSR heat can be used as a grid sink for excess Wind and Solar electric power production. This system negates any need for grid-based electric power storage and is highly complementary to wind and solar power production. The cheap and effective salt-based thermal storage would act as an energy battery that will allow the demand curve to be supplied at the appropriate service levels without damaging surges taxing the grid system.

Studies conducted by Terrestrial Energy USA and Idaho National Laboratory (INL) have shown that the IMSR power plants would be an effective system, relative to all other systems under review, to provide a growing water supply and stable power to the grid. The expanding growth demands on power and water can be served by an IMSR — a low-cost, carbon-free source of inherently safe energy.

H2 from High Temperature Steam Electrolysis

Making H2 from natural gas is the dominant method today, but is highly sensitive to NG input prices. The (IMSR) is uniquely suited to provide a reliable and secure alternative method for H2 production that has negligible input price volatility. The IMSR’s can deliver the temperatures (600C+) and electric power that are needed for alternative methods for H2 and O2 production.

Terrestrial Energy USA and Idaho Nation Laboratory (INL) have shown that the IMSR would be the most effective system of those reviewed to date to enable the best method of clean cost-competitive H2 supply.

Analysis by INL and Terrestrial USA have shown that the IMSR is highly suited to be coupled to an industrial facility using High Temperature Steam Electrolysis for H2 production. Findings of the studies show that there are many other H2, O2, NH3 and heat power production combinations that can be tailored to a great number of industrial applications.

Synthesized Transport Fuels

Production of transport fuels, including gasoline, using the IMSR, processes heat and electricity at a cost-competitive positon with fossil fuels and represents a dramatic shift in economics of liquid fuel synthesis technology. This shift could have a profound effect on the industrial production methodologies of a broad range of valuable chemicals and fuels used in our industrial society. Demonstrating the production of synthetic gasoline at an industrial scale will certainly be followed closely by the production of other fuels such as aviation fuels, LPG, Diesel and others.

Gasoline is also a symbolic fuel the public is familiar with and would give a clear signal of the immense opportunities that synthetically-derived fuels from nuclear power-driven process heat would represent. Namely: stabilized cost of energy inputs, sequestration of atmospheric carbon, and economic alternatives to fossil fuels. All of these opportunities are symbolic of the potential of IMSR to be a transformative technology and enables many new innovations and competitive clean industrial technologies that combine to drive economic growth and deep decarbonization of primary energy systems.

Ammonia Production Coupled to IMSR:

During 2016, thirty plants produced 9.4 million metric tonnes of ammonia (NH3), principally based on the Haber-Bosch reaction processes. The principal feedstock to these plants is natural gas, which is reformed with steam to produce a target stoichiometric gas mixture of CO2, N2, and H2. Sorbents are used to remove CO2 and other contaminants prior to synthesizing NH3. Ammonia is used to produce a wide variety of fertilizers, nitric acid, fuels, and amine-based chemicals used broadly in industrial agriculture.

The above opportunities are examples of how IMSR can benefit the large and growing ammonia industry. Hydrogen that can be produced by high temperature steam electrolysis (HTSE) can replace the fossil-fuel intensive steam methane reforming technique. This would eliminate CO2 emissions associated with hydrogen production today. The economics of HTSE when compared with fossil fuel-based hydrogen production, are based on the value of Green House Gas (GHG) emissions avoidance, as well as the market value of oxygen production for industrial uses, which represents a valuable byproduct of the HTSE process. Another possible opportunity for IMSR is for a modified interface with either a conventional or a revised steam methane reforming plant – a similar system to one used for methanol production. The significant benefits of a novel and disruptive NH3 economy can be brought rapidly to fruition with the hybrid coupling of IMSR process heat with large scale ammonia production.

Coupling IMSR Technology into Direct Reduction Steel with H2

It has been estimated, in the studies conducted at INL, that hydrogen-based high performance steel making could be cost-competitive with traditional steel production when coupled to an IMSR hybrid energy H2 production system. This could also reduce total CO2 emissions from steel production by 80 percent (Fischedick et al. 2014b).


John Kutsch is vice president of Business Development for Terrestrial Energy USA.