Posted by Suzanna Hinson

Last year, an exciting development occurred for advanced nuclear power: Molten salt reactor (MSR) investigation won funding from the Technology Strategy Board. The Alvin Weinberg Foundation welcomed the development, writing “MSRs could be a game-changing way of producing clean electricity, so this is great news for all who support the revival of clean energy R&D to tackle climate change”. The bid was led by Jasper Tomlinson, Professor Trevor Griffiths, and project manager Rory O’Sullivan, who together planned to produce the UKs first rigorous study of the feasibility of a pilot-scale MSR. And the results are now in.

The review not only argues the necessity of nuclear power, but seeks to answer the questions of how to pursue it. Current nuclear deployment appears, the study states, to be locked into old solid-fuelled technology, with little innovation since the 1970s and even less development of advanced options such as MSRs. Previous reviews of MSRs, such as the Generation VI Forum January 2014 Report, have concluded that the technology is one of the furthest from commercial deployment. However much has been achieved in the MSR world in recent years, and taking into account the latest developments this publication concludes that the time is now right for a “commitment to an agenda to proceed with a molten salt reactor programme”. Six different reactor options were assessed in the MSR review:

  • Fibre Energy’s Liquid Fluoride Thorium Reactor (LFTR),
  • Martingale’s ThorCon,
  • Moltex Energy’s Stable Salt Reactor
  • Seaborg Technologies – Seaborg Waste Burner
  • Terrestrial Energy’s Integral MSR
  • Transatomic Power Reactor

All six display the advantageous characteristics of using molten salt as fuel and coolant including safety, less waste, higher thermal efficiency, fuel cycle flexibility (including the ability to use up the plutonium stockpile as fuel) and co-generation opportunities afforded by the high temperatures at which the reactors operate. Despite finding advantages in all the reactor designs, the review concludes that The Stable Salt Reactor, the design proposed by Moltex Energy, is the best option to pursue. The Stable Salt Reactor is a fast spectrum pool type reactor but its unique characteristic compared with the other designs is that the fuel is static.

Most Molten Salt reactors involve the highly radioactive liquid being actively pumped through a heat exchanger while the Moltex design encases the radioactive molten salt (a fraction of spent nuclear fuel mixed with sodium chloride to reduce its melting point) within metal tubes, similar to the fuel rods in traditional reactors. The flow of molten salt in the tubes is entirely by natural convection with no moving parts involved meaning no possibility of pump failure. The pool of coolant is another molten salt that makes the reactor intrinsically safe since any leakage of radioactive fuel is mixed and diluted in the large pool of coolant. Unlike all other molten salt reactor designs, this design in not a derivative of the Molten Salt Reactor Experiment developed at Oak Ridge National Laboratory (where MSR designs were initially developed in the 1960s) and is instead a truly 21st century design. Along with a whole host of benefits the Stable Salt Reactor is designed so that all components can be constructed in segments and assembled at any given site. This modular design is far simpler and more affordable than todays reactors and makes deployment all the more attractive.

The report concludes that this UK designed reactor, “due to its relative simplicity and relatively few and low technical hurdles, is the most suitable configuration for immediate pilot scale development in the UK”. Regardless of the specific reactor, the report also outlines the general advantages to the UK of pursuing an MSR program. Britain’s role as a leader in nuclear power has been declining since the 1970s with no new plant built since Sizewell-B in 1987. Currently, the UK has a non-existent nuclear R&D spend compared with other countries. However, the advantages of redeveloping our nuclear strength are many, including manufacturing growth, employment, energy security, reduced waste insecurity, positive contribution to carbon reduction targets, and technology export potential. With clear advantages, and a promising design to develop in the Stable Salt Reactor, it must be hoped the government, in the midst of scrapping subsidies and despairing over delays at Hinkley C, see the prosperity an MSR program could bring.  


  1. wayne proctor says:

    Seaborg Technologies – Seaborg Waste Burner has the best label for getting those fearful of atomic energy/ nuclear reactors interested. Of all the hurdles in front of development, fear is going to be the highest one to clear. IMHO

    • Charles Barton says:

      Maybe a quick, low cost path to useful MSR technology is more important than a PR. ploy. I have recently posted on my blog Nuclear Green some responses to the MSR Review. My responses dealt with some issues the Review writers failed to take into account.

  2. Charles Barton says:

    The report reflects several flaws. First it does not establish criteria for determining the relative value of the various reactor projects it considers. Secondly, it failed to evaluate the use of existing technologies it proposed reactor designs. Three North American MSR projects are under development and either have reached a pre-conceptual phase or will reach that phase within the next two years. One project has stated that it expects to complete a commercial prototype in 2021, and already has customers lined up. Thirdly, I believe that the stationary fuel concept was looked at in Oak Ridge, during the early (K-25) phase of the Aircraft Nuclear Propultion project It was discarded in favor of flowing fuel. This is by itself a potential minor flaw in the report. A more major flaw would be its failure to justify its perfered technology conclusions, which would discard lots of very valuable ORNL research, and launch would be developers on a very long and potenually arduous research path. The report writers failed to see that there was good reason why all of the North American MSRs were planning to use the Technology that Alvin Weinberg helped to dfr\\evelop at ORNL.

    • Ian Scott says:

      Charles, just to address your point about the ARE team discarding the concept of static molten salt fuel. That decision (I thank Kirk S. for bringing it to my attention) was made on the basis that thermal conductivity in molten salts is very low – about 1/10th that of uranium oxide – and they calculated that tubes would have to be <2mm diameter to avoid the salt boiling. They ignored the fact that convection is a far more important mechanism for heat flow in liquids than conduction – presumably because they were designing an aircraft engine and rapidly varying g forces would play havoc with convection.

      We at Moltex Energy did what they did not (and actually scientifically could not) do which is apply modern CFD techniques to calculate the impact of convection. We established that tubes the diameter of those used in conventional reactors would allow very high power levels to be achieved – provided the reactor stayed firmly on the ground!

      As a result, our design can draw on half a century of large scale active development of fuel assemblies rather than the few years of limited development that the MSRE achieved. It is actually only a relatively small step away from current reactors – but it carries virtually all the enormous advantages of the use of molten salt fuel while having far fewer engineering challenges to overcome.

      I share with you though, your regret that the EPD report did not provide a detailed technical justification for their recommending the Moltex Energy design. I think that would have been a very useful contribution to the MSR community.

  3. Kirk Sorensen says:

    This was not a comprehensive review because Flibe Energy’s LFTR concept, along with several others, did not do a full technical release to those who did the study. This decision was made for several reasons, including protection of intellectual property, uncertainty about the export of technology, and competitive advantage, but it rendered the result highly suspect. I am not faulting those who did the study, indeed, I spent a great deal of time with them when they visited Huntsville, Alabama. But to paint the result as a “comprehensive analysis” leading to the selection of the Moltex concept is totally misleading.

  4. James Spooner says:

    My chemical engineering is close to a half century out of date, so I will comment from the position of a near layman. A paramount design element of any nuclear energy proposal must address radioactive waste. A prime objective of any new technology must address not only the waste of the technology under consideration, bat also the disposal of existing waste. The Seaborg Waste Burner does that and I suspect the others can be modified if they are not already capable.

    Include that discussion in future analyses.

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