Monday, 27 September 2021

Part 4 – Safer Nuclear Power using Molten Salt and Thorium Reactors

 Molten salt reactors mean inherently safe nuclear electricity

In view of their potential safety issues a shift away from PWR’s and fast breeders, designed in the 60's and 70's, towards new inherently safe plants would be very welcome.  Ideally these should: 

  • operate at atmospheric pressure and so couldn’t explode; 
  • be unable to overheat or meltdown; 
  • be designed to be walk-away-safe in the event of power failure; 
  • have a negative temperature coefficient of reactivity: meaning that as the reactor temperature increases its output reduces;
  • allow load following and rapid output changes;
  • produce much less waste with a much shorter radio-active half-life. 

Of the various proposed Generation IV nuclear reactor designs there is one which fulfils all of these criteria, the liquid fuelled thorium reactor (LFTR).

On 14th July 2011, thanks to Ken Pottinger (now sadly deceased) of French News Online, I became aware of an alternative to current PWR technologies, which is based on 
liquid fuelled thorium reactors LFTRs and the Molten Salt Reactor Experiment. In this context a salt is the chemical term for a compound of a metal and a halide such as a fluoride or a chloride e.g. lithium fluoride. At the time I had no idea that nuclear reactors could have many design variants and even work in the liquid phase.  I spent several days researching the topic and wrote this piece on my blog summarizing my findings. 

The molten salt reactor experiment

A prototype molten salt reactor, operating at atmospheric pressure, ran at Oak Ridge National Nuclear Laboratory (ORNL), Tenessee in the 60’s and 70's.  The film below, made at the time, shows how this pilot scale plant was designed,built and operated.

The Molten Salt Reactor Experiment (MSRE) ran for more than 13,000 hours at full power, without significant materials problems, and successfully demonstrated the viability of the concept.  At the weekends, when they didn’t want to have staff on duty, they used to turn off the power, the fan cooling the freeze valve below the reactor vessel would stop, the plug of solid salt would melt and the reactor contents would drain by gravity into storage tanks which were configured to not allow a critical mass to form and therefore the chain reaction would stop. It was truly walk away safe!

To turn it into a commercial product there is more development work needed on the optimization of the waste processing stages, and also on the materials necessary to resist the high temperature and intense radiation environment over the long term. At the time that the project was shut down, ORNL had already started to work on these areas. We are fortunate that the work on the MSRE at Oak Ridge was very fully documented and these documents are in the public domain.

The fuel used for the MSRE was Uranium 233 produced in a reactor at Hanford. It was intended that at a future stage the reactor design would be modified to work as a breeder reactor producing U233 from Thorium 232 in a self-sustaining way. This would require the development of a chemical process to separate the U233 formed in the blanket and send it to the reactor. Unfortunately the project was shut down before this was fully progressed.

Kirk Sorensen has been actively promoting this technology and he explains in this video how he came to rediscover molten salt reactors and Thorium as an alternative fuel.

What about nuclear waste?
But the specific concern of many people is with the management of nuclear waste. 

The composition and quantity of nuclear waste depends on the fuel used in the reactor and the degree to which the fuel is burned.  Pressurised water reactors running on the Uranium 235/238 fuel cycle can only burn about 4-5% of the fuel contained in their fuel rods, which deteriorate and have to be replaced every 18 months.  During this operation the reactor is taken out of service.

Liquid fuelled reactors can burn a much larger percentage of their fuel than solid fuelled reactors, because it’s so much easier to remove gaseous fission products like Xenon 137, which poison nuclear reactions by absorbing neutrons.  Also, by incorporating a side-stream, carrying the molten salt fuel for waste removal and fuel addition, there is no need to shutdown the reactor for these processes. Therefore, for the same amount of energy generated, molten salt reactors can produce 35 times less waste. 

LFTR versions running on Thorium also produce waste with a much shorter half-life of 300 years as opposed to tens of thousands of years.  This very clear video, again from Kirk Sorensen with others
explains how fission products are created and what they can be used for.

 In this rather more detailed video Kirk Sorensen projects forward the results of radioactive decay over time on waste from the Uranium 235/238 fuel cycle.  He expands on the idea of recycling nuclear waste and asks, is it really all waste? 

But as Kirk Sorensen says in an earlier video, you can also dispose of waste from PWR’s using liquid fuelled waste burning reactors, which also generate power and this is described more fully later.

Energy cheaper than coal

But without internationally agreed and binding carbon taxes, which would make fossil fuels more expensive, safer nuclear power just won't happen unless it’s cheaper than other options. 
Robert Hargraves develops the argument that in order to replace fossil fuel burning power plants you must be able to generate electricity by low carbon methods at an overall cost less than that of fossil fuels. 
In this detailed talk he examines the costs of generating electricity from different sources including wind and solar.  He also proposes using liquid fuelled reactors and points out that the higher operating temperatures of such reactors offer higher power generation efficiencies as well as various options to use the high temperature heat to directly drive chemical reactions.

And cheaper than unsubsidized renewables

At the beginning of the next video Ian Scott of Moltex Energy reaffirms the importance of radical innovation to enable new nuclear power investment to find a role in a commercial environment where the penetration of renewables is significant.  This means finding ways to reduce construction and regulatory costs by modularisation and factory production techniques so that new nuclear plants can still be profitable at 50% utilisation factors. In this video he describes the Moltex Waste Burner which is being developed in New Brunswick, Canada by the North American incarnation of his company, with the full support of central and local government.

If you’ve got this far you are probably suffering from information overload but congratulations on your persistence! 

Why haven’t molten salt reactors been developed before?

When I first researched liquid fuelled reactors burning thorium (LFTRs) I found it hard not to think that there was something that was being hidden from me.  Such as some reasons that explained why such obviously better technology hadn’t been developed! Finally I was convinced that there isn’t anything of the sort, and the reasons why it has languished for 60 years are almost entirely political in origin.  This Google Tech Talk, again by Kirk Sorensen, explains the background. 

Where will safer nuclear power happen first?

Nuclear power is, a complex subject difficult to explain to non-specialists, or the general public, and it can’t be fitted into a few tweets for people with short attention spans or other priorities.  Unfortunately it’s much easier to invoke fear among the public of accidental releases of radioactive materials; so a sustained campaign of education is required to overcome decades of nuclear scepticism and deliberate misinformation that has stuck in the minds of the public.  The success or otherwise of such public education will be a factor in determining where new nuclear power will be developed.

Western European countries especially France and the UK have the necessary infrastructure, but I doubt that they have the political will and in the case of the UK, the resources, to take any sort of lead in developing new nuclear designs beyond the feasibility stage. Luckily other countries are better placed. The following is by no means an exhaustive list but only a selection of the most likely candidates to take new nuclear designs to full scale commercialization.

The United States

There are many opportunities for the US government to fund research into up-scaling advanced nuclear reactors and their much safer technology. 

For example, the US Department of Energy DOE is financing research into several initiatives intended to enable cost reductions in nuclear construction projects. 

In June 2021, in response to the announcement by the Biden-Harris administration of their policy to aim for net zero carbon emissions by 2050, the Office of Nuclear Energy has requested 1.8 billion dollars from Congress.  To quote from their press release,

 Quote <<The expansion of nuclear power will be critical to reaching net-zero emissions by 2050 and there’s an urgent need to bring new clean energy technologies to bear.  This budget request puts a tremendous emphasis on scaling up the commercial deployment of smaller and more flexible advanced reactor designs, and to the advanced fuel that will be required to operate them.” >> Unquote

 Let’s hope that this request will be granted and the money wisely spent.

 There are also numerous privately funded companies which have announced programmes to develop liquid fuelled reactors.  It remains to be seen whether this multi-pronged effort can surmount the burdensome costs and difficulties that will arise when they submit their designs for approval by regulatory agencies which are unfamiliar with this technology.  In this context governments can really help to advance the approval of innovative technologies by questioning and revising approval procedures, clearing pathways and providing seed funding for research. 

 The cost of approval and licensing

In the case of the USA, a few years ago, it seemed to me unlikely that these companies could persuade regulatory agencies to reduce the one to two billion dollar cost and ten year timescale that the US Government Audit Office estimated in July 2015 that it would take to certify and license a fundamentally new design. At present the US Nuclear Regulatory Commission requires a fully developed design to review, so that companies would have to spend a very large amount of money upfront. Faced with this situation private investors just won't bother or they will migrate to jurisdictions which are more welcoming and which proceed by a staged approval process.

More recently in the USA there has been a change in the mood and, helped by international pressures and extreme weather events around the globe, there is renewed impetus towards addressing the climate crisis and a political will building around the development of carbon free energy from innovative nuclear technology.

Small modular reactors - Executive Order 13972

One of the last actions of the outgoing Trump Administration was to persuade him to sign Executive Order 13972 of January 5, 2021.

Promoting Small Modular Reactors for National Defense and Space Exploration”

 This order, among other things, specifically mandates the Secretary of Defense to look into:

Quote <<Sec. 3. Demonstration of Commercial Reactors to Enhance Energy Flexibility at a Defense Installation. (a) Micro-reactors have the potential to enhance energy flexibility and energy security at domestic military installations in remote locations. Accordingly, the Secretary of Defense shall, within 180 days of the date of this order, establish and implement a plan to demonstrate the energy flexibility capability and cost effectiveness of a Nuclear Regulatory Commission-licensed micro-reactor at a domestic military installation.>> Unquote

A few years ago Kirk Sorensen was hoping to bypass national nuclear regulatory procedures by installing an LFTR on a military site but unfortunately this order invokes the NRC licensing process.  Assuming that the order progresses through the Biden Administration, perhaps Kirk can find a way to speed up and simplify certification.


As a result of its history of nuclear innovation, and years of operational experience with CANDU heavy water reactors, Canada has an industrial, intellectual, regulatory and political infrastructure which is favourable to advances in nuclear power.  Its staged regulatory process is particularly helpful to innovative technologies.

 This is already being demonstrated in New Brunswick by Moltex with theirwaste burning, molten salt in tubes - reactor concept and associated GridReserve storage technology.


Quoting from their press release of Tuesday, May 25, 2021

Quote <<Moltex Energy is delighted to have completed Phase 1 of the Canadian Nuclear Safety Commission’s (CNSC) Pre-Licensing Vendor Design Review (VDR) for Moltex’s 300 MW Stable Salt Reactor – Wasteburner (SSR-W). The CNSC concluded that Moltex has a clear understanding of the Canadian regulatory requirements and expectations. >> Unquote


Terrestrial Energy, another Canadian-based company, is developing a Denatured Molten Salt Reactor (DMSR) design called the Integral Molten Salt Reactor (IMSR). The IMSR is designed to be deployable as a small modular reactor (SMR). Their design currently undergoing licensing is 400MW thermal (190MW electrical). With high operating temperatures, the IMSR has applications in industrial heat markets as well as traditional power markets. The main design features include neutron moderation from graphite, fuelling with low-enriched uranium and a compact and replaceable Core-unit. Decay heat is removed passively using nitrogen (with air as an emergency alternative). The latter feature permits the operational simplicity necessary for industrial deployment.

Terrestrial Energy completed the first phase of a pre-licensing review by the Canadian Nuclear Safety Commission in 2017, which provided a regulatory opinion that the design features are generally safe enough to eventually obtain a license to construct the reactor.


Due to the language barrier, and the Chinese tendency to be cautious about public announcements, it’s difficult to accurately follow China’s progress towards implementing molten salt reactors. Western press reports are often sketchy, inaccurate and journalistic, but it does seem that they are making good progress towards starting up a molten salt reactor at their research facility in the desert region of Wuwei very soon.


In January 2011 Chinese Academy of Sciences initiated a thorium molten-salt reactor research project.  A 100 MW demonstrator of the solid fuel version (TMSR-SF), based on pebble bed technology, was planned to be ready by 2024.  Initially, a 10 MW pilot and a larger demonstrator of the liquid fuel (TMSR-LF) variant were targeted for 2024 and 2035, respectively.  China then accelerated its program to build two 12 MW reactors underground at the Wuwei research facilities by 2020, beginning with the TMSR-LF1 prototype. The project sought to test new corrosion-resistant materials.  By 2021 China stated that the Wuwei prototype Molten Salt Reactor could start-up in September. We are waiting to hear what they have achieved.

As a result of that investment, and less lengthy certification requirements, China is most likely to be the first to recreate the Molten Salt Reactor Experiment and develop it further to a commercial design for completion in 2030.  They will then patent their designs and sell them internationally. 

I wish them every success!



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