Energy and Climate Change CommitteeWritten evidence submitted by the Weinberg Foundation (NUC 20)


This submission presents the case for substantially increased Government funding for research and development into thorium-fuelled nuclear fission.

Thorium has many advantages over uranium including being more abundant, more energy dense and producing significantly easier to manage waste products.

New reactor designs, such as the molten salt reactor, can also drastically reduce the generation of waste and offer other significant safety and efficiency advantages over current reactor designs.

A prominent molten salt reactor design, the Liquid Fluoride Thorium Reactor (LFTR), offers inherent safety features, generates very small quantities of waste and can use legacy waste as fuel. In addition, it is proliferation resistant, more efficient and less costly to construct than current reactor designs.

1. I am writing to the Committee as CEO of The Weinberg Foundation, a not-for-profit organisation set up to promote thorium-fuelled molten salt reactors, a technology pioneered in the 1960s by Alvin Weinberg, Director of the US Oak Ridge National Laboratory.

2. The withdrawal of EON and RWE from the Horizon coalition serves as a reminder that current market conditions do not provide an attractive investment climate even with policy interventions to provide contracts for difference and a supported carbon price. One of the reasons why the expected nuclear new build is proving more difficult to deliver than we might wish, is that currently our use of nuclear power is restricted to a very narrow range of technologies in the uranium fuel cycle. There are many potential new technologies and fuel types that could usher in a genuine nuclear renaissance.

3. Whilst funding for fission research has dropped to a very low level in the UK, in other countries it is continuing and increasing. China and India are, for example, now investing considerable resources into a range of new technologies including reactors using thorium. Thorium has many advantages over uranium including being more abundant, more energy dense and producing significantly easier to manage waste products. Reserves of thorium are widely dispersed around the world with large deposits in Australia, the USA, Turkey and India. China also has substantial thorium reserves, especially within its rare earth mineral deposits in Inner Mongolia. In Europe, Norway has 132,000 tons of proven reserves, 5% of the world’s total.

4. Thorium is not fissile and therefore cannot sustain a nuclear chain reaction on its own. However, it is fertile, which means that if it is bombarded by neutrons from a separate fissile driver material (Uranium-233, Uranium-235 or Plutonium-239) or from a particle accelerator it will transmute into the fissile element Uranium-233 (U-233) which is an excellent nuclear fuel.

5. New reactor designs using thorium as fuel can drastically reduce the generation of waste and offer other significant safety and efficiency advantages over the current reactor designs. Thorium-fuelled molten salt reactors, can also be used to permanently dispose of existing high-level waste inventories, generating power and valuable medical isotopes in the process. Molten Salt Reactors (MSRs) are fuelled by liquid forms of fissile and/or fertile elements such as uranium, plutonium and thorium dissolved in a fluid of molten salts. In an MSR the radioactive fluid circulates between the reactor core and a heat exchanger. The heat generated in the reactor drives a turbine which generates electricity.

6. Interest in MSRs has grown since 2002 when the MSR was chosen by the Generation IV International Forum as one of the six most promising designs for future nuclear reactors. In January 2011, the Chinese Academy of Sciences announced a Government-funded $500 million research and development (R&D) programme into thorium-fuelled MSRs. France’s National Centre for Scientific Research (CNRS) has had an MSR R&D programme since 1997, and a number of private companies in the US, Japan, Australia and the Czech Republic are currently developing thorium-fuelled MSR designs.

7. A prominent thorium-fuelled molten salt reactor design is the Liquid Fluoride Thorium Reactor (LFTR) Two-Fluid “Core and Blanket” design. The reactor core contains fissile fuel (U-233, U-235 or Pu-239 in liquid fluoride form) held in a graphite container which acts as a neutron moderator. The core is surrounded by an outer vessel, the blanket, which contains thorium dissolved in a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2) known as FLiBe. When the fuel in the core fissions, neutrons are released which penetrate the walls of the core and bombard the surrounding blanket of thorium causing it to transmute into U-233. The U-233 is transferred to the core and new thorium is added to the blanket.

8. The LFTR contains two separate piping loops. The first loop carries the liquid thorium into a decay tank where the U-233 can be moved to the inner core. The second loop transfers the heated U-233 molten salt from the inner core to the heat exchanger which drives a turbine which generates electricity. The U-233 salt is then transferred back to the reactor core to continue fissioning. The amount of fuel the reactor breeds is equal to the amount that it consumes. To keep the fission reaction going, thorium must be added to the reactor at the same rate that it generates and consumes uranium. After a year of continuous operation, the starter fissile fuel in the reactor will be depleted and the reactor is able to run on U-233 produced from the thorium blanket.

LFTR Safety Features

9. As fuel in a LFTR is already in liquid form, it cannot melt down, as solid fuel rods in a Light Water Reactor (LWR) can. In addition, the LFTR’s large negative temperature coefficient means that regulation of the reactor’s temperature is passive. There is no need for control rods or an active cooling system. The molten salt expands as a result of the heat generated by fission, which slows the rate of fission. The reduction in fission heat cools the salt, which in turn leads to an increase in the rate of fission. In other words, as the reactor temperature rises, the reactivity decreases. The reactor thus automatically reduces its activity if it overheats. The concentration of thorium fuel in the blanket can be adjusted at any time, which provides further control over the level of reactivity in the core.

10. The LFTR can only overheat if the circulation of the molten salt is disrupted as a result of a loss of power, thereby preventing heat removal from the core. If that should happen, the build-up of excess heat melts a freeze plug of solidified salt at the bottom of the reactor, allowing the molten salt to drain into a separate tank. Once in the tank, the fission reaction stops and the liquid fuel cools down and becomes an inert solid mass. This is an entirely passive process requiring no external power source.

11. In an LWR, water must be kept at high pressure to raise its boiling temperature. The LFTR’s operating temperature is around 750ºC, while molten salt boils at around 1,400ºC, which means that reactor pressure remains at atmospheric levels, thus eliminating completely the risk of a pressure explosion. With no need for pressure vessels and other elaborate containment structures, the cost and size of a LFTR is substantially less than an LWR.

12. If the ceramic fuel pellets in a LWR melt down, gaseous fission products can be released, and in the event of a steam explosion, these products can be carried and dispersed into the environment by wind and water. Given the low pressure in a LFTR, if molten salt fuel should leak from the reactor, it simply spills onto the reactor room floor, where it solidifies on contact with the ground becoming an inert mass. The fissile fuel remains locked inside the rock and can be reused.

13. As molten fluoride salt is heavy, it cannot be dispersed by wind or carried by moving water. In the very unlikely event of a terrorist attack or missile strike on the reactor, spilled fuel would create a small contamination zone in the immediate surroundings of the reactor. To prevent leaching of radioactive material into soil or groundwater following a spill, LFTRs can be built in protective bunkers which create an impervious barrier between any spill and the surrounding land.

LFTR—Low Waste Generation & Removal of Fission Products

14. Nuclear reactors produce two kinds of radiotoxic waste—fission products (FPs) and long-lived transuranic elements such as plutonium. FPs such as Xenon absorb neutrons and slow down the fission reaction, reducing the efficiency of a reactor. After 12 to 18 months the solid fuel rods in an LWR are rendered unusable by the build up of these neutron absorbing FPs, thus preventing the bulk of the energy in the fuel from being exploited. When this happens, the reactor must be shut down so that refuelling can take place. The hazardous spent fuel from a LWR must be safely stored for around 10,000 years.

15. As FPs can be removed from a LFTR during operation, the reactor can fission almost all of its fuel including its own transuranic products. This means that LFTRs produce almost no long-term waste and very little short-term waste, while achieving near total burn up of the fuel. For this reason, the energy produced by one ton of thorium in a LFTR is equivalent to that produced by 250 tons of uranium in an LWR.

16. In a LFTR valuable FPs such as Xenon and Krypton gas can be removed and sold for medical, industrial and scientific research purposes. The molten salt fluid is pumped from the reactor into a chemical processing unit which separates the fission products and transfers them to armoured storage casks. The small volume of fission products with no market value can be safely stored in casks, where most will become inert within 30 years. Only 17% of FPs from a LFTR have long half-lives and these will require safe storage for up to 300 years.

LFTR—Inherent Proliferation Resistance

17. The U-233 produced in a LFTR is contaminated by U-232 which emits heat and strong gamma radiation, both of which damage weapons components and circuitry. For this reason, no nuclear weapons programme has ever made use of U-233, and as the International Atomic Energy Authority (IAEA) has noted, any future development of weapons based on U-233 would be difficult.1 It is not possible to enrich thorium to produce weapons grade material. In addition, LFTRs produce only very small amounts of plutonium which further reduces any proliferation risk.

LFTR—Consumption of Spent Fuel

18. LFTRs can consume spent fuel from other reactors. As well as providing the initial fissile stimulus for the thorium-uranium cycle, spent fuel can be processed for reuse in a vat of molten salt. During reprocessing, FPs can be isolated and sold, while the transuranics can be collected and used to fuel a LFTR. LFTRs can also use fissile material from dismantled weapons as fuel.2

LFTR—Low Capital Costs and Fast Construction

19. The efficiency of LFTR design and structure suggest construction costs will be favourable. No pressurised containment vessel is required, as LFTRs operate at atmospheric pressure. Fewer safety mechanisms are necessary, as LFTRs have intrinsic safety features. Molten salts are effective coolants with high heat capacity which means that components such as pumps and heat exchangers can be compact. In MSRs there are no fuel rods to be constructed or replaced, and no spent fuel rods to be processed.

20. LFTRs can be small and modular (producing up to 300MW) which would suit power needs in remote locations, factories and military bases. Small Modular Reactors (SMRs) can be built in a central factory and assembled on site. It is also possible to combine SMRs to form a larger power station if required. A production line approach has the potential to generate economies of scale and result in quick delivery of a functioning reactor. In addition, as LFTRs do not require water to operate, they can be constructed near to or within urban areas, reducing the need for transmission infrastructure. LFTRs could also be constructed adjacent to industrial sites so that waste heat from the reactor can be used for heat-intensive processes such as desalination, or the production of aluminium, cement, ammonia and synthesised fuels.

21. Five cost studies have indicated that the capital cost of MSRs would be $1.98/watt, cheaper than both a coal plant ($2.30/watt) and a LWR ($4/watt).3 This equates to an overall cost of approximately $200 million per 100MW reactor.


22. The UK has a great history of innovative research in nuclear technologies and we strongly believe that strategic investment now could help us to regain a lead. We believe, given the Government’s commitment to nuclear power, we should significantly increase funding for R&D into thorium-fuelled molten salt reactors. This would put us in a strong position to enter into enhanced international collaborations and ensure we maintain a strong skill base, enabling us to assess properly the new reactor designs that are being developed in other countries.

July 2012

1 IAEA, Bulletin 51-1, “Exploring Fuel Alternatives”, 2009.

2 Gat, Engel & Dodds, “Molten Salt Reactors for Burning Dismantled Weapons Fuel”, Oak Ridge National Laboratory, 1992, accessible online at

3 Hargraves & Moir, “Liquid Fluoride Thorium Reactors”, Physics and Society, Vol 40, No 1 January 2011, p 9.

Prepared 1st March 2013