Friday, 15 July 2011

Thorium- A New Direction in Power Generation


I had one of those rare experiences last night when I heard about something entirely new to me which has the potential to completely change an important aspect of the world. A safer alternative to the uranium-plutonium fuel cycle, currently used in all nuclear power stations, exists. I'm talking about the use of thorium as a nuclear fuel.
This video of a TED talk by Kirk Sorensen, who set up the blog "energy from thorium",  summarises the case for thorium in a clear and simple way.



If you still want to know more carry on reading the rest of this blog post.

The Advantages of Thorium Fuelled Reactors

Less Dangerous - Reactors, using generation IV molten salt designs, have a greatly reduced risk of an escape of highly radioactive materials as a result of an explosion, meltdown or fire following an earthquake, tsunami or system failure. There is nothing to burn or melt down.

Less Radioactive Waste - They produce a small fraction of the radioactive wastes associated with the uranium/plutonium fuel cycle and they do not have to be stored for tens of thousands of years.

Less Expensive – They don’t use raw materials like uranium, which are scarce and expensive, neither do they need massively strong containment structures.

Less Need for Potentially Dangerous Fuel - They only require fissile materials, (with a potential to make nuclear weapons), to start them up. Afterwards they are self-sustaining.

Less Risk of Proliferation - They don’t generate fissile materials and therefore the risk of proliferation of nuclear weapons is much reduced.

Thorium’s Advantages in More Detail
Less Dangerous - The generation IV molten salt reactor designs, in their breeder form, use liquid thorium fluoride ThF4 mixed with other fluorides as a fuel.  They run at atmospheric pressure so there is no risk of explosion of the reactor vessel. They incorporate a refrigerated plug, which melts if there's a power failure, and the liquid core is then discharged by gravity into tanks, which are arranged so that there is not a critical mass of radioactive material in one place, and the reaction stops. Thorium fluoride does not burn in air. There are no solid fuel rods to meltdown.  Because there are no fuel rods, and waste is removed from the liquid core, there is no need to shut down the reactor for waste removal and no need for personnel to manipulate fuel rods.

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Less Radioactive Wastes - The supporters of thorium powered reactors claim that they generate about 35 times less waste from spent fuel, a fraction of the nuclear waste generated by a uranium fuelled reactor with only 17% of the waste having a long half life.  They also state that a Liquid Fluoride Thorium Reactor (LFTR pronounced lifter) burns its fuel much more completely than a solid fuel reactor and therefore produces much more power for the quantity of waste generated.  Click the arrow on the flash movie below to see a comparison between uranium and thorium fuel/waste cycles.
  


Not working? Get the Flash Player to see this flash movie.
Extracted from Joe Bonometti's 55 minute, 2008 Google Tech Talk.  See below.

A variant of the design using liquid chlorides and fast spectrum neutrons can “burn” wastes from the uranium/plutonium fuel cycle and would be very useful as a complementary waste disposal technology for the existing stock of nuclear reactors. This 2003 paper from Charles Forsberg at Oak Ridge discusses "Coupling Spent Fuel Processing with Actinide Burning using Molten Salt Reactors".

Less Expensive - Thorium is four times more abundant than uranium and it’s widespread in the earth’s crust.  It is cheap and is a by product of the extraction of rare earths from Monazite sands already mined around the world. Uranium costs $121/kg (equivalent to $55/pound which rose to a high in 2007 of $136/pound). Thorium is not currently quoted as a metal in commercial quantities because its previous industrial uses were replaced in the 80’s by non-radioactive substitutes. In 1979 it was quoted at $33/kg, a price which had remained stable since 1964. The US has recently buried 3200 tonnes of thorium nitrate in the Nevada desert due to lack of demand. It has 20% of world reserves of thorium. To generate enough electricity to supply the whole of the US for a year would require 400 tonnes of thorium, if it was all generated using liquid fluoride reactors. A single mine in Idaho could produce 4,500 tonnes of thorium per year.  China, although it is not mentioned in this table, also has ample reserves and is quoted here as having 300,000 tons, which is enough to last it for 300 years.

Less Need for Potentially Dangerous Fuel - Unlike uranium, naturally occurring thorium does not need isotope separation to enrich it before it becomes suitable for use in reactors. The naturally occurring form of thorium is 232Th is only mildly radioactive and cannot be used to make weapons.

Less Risk of Proliferation - Inside the breeder version of the reactor Thorium is converted to 233U. There has only ever been one operational nuclear weapon that has used 233U as its fissile material, despite the ease of manufacturing 233U from abundant natural thorium. It was part of a test series in 1955 called "Operation Teapot".  When 233U is used as a nuclear fuel, it is inevitably contaminated with 232U, which decays rather quickly (78 year half-life) and whose decay chain includes thallium-208. 208Tl is a “hard” gamma emitter, which makes any uranium contaminated with 232U nearly worthless for both official and clandestine nuclear weapons since the gamma radiation would damage electronics and is easily detected because of its unique signature. 233U with very low 232U contamination could be generated in special reactors like Hanford, but not in reactors that use the 233U as fuel.

So Why Did Everyone Take the Uranium/Plutonium Road?

The origins of nuclear power generation are rooted in the drive to create nuclear weapons which started in 1942 with the Manhattan Project in the USA.  Although one thorium based bomb was tested later it was generally considered that thorium did not have weapons potential and, under the extreme pressure of the Second World War, the uranium route was chosen and rapidly implemented. After the war, when nuclear reactors for producing electricity were developed, it was considered at the time that uranium was a scarce and expensive resource. The perceived need to continue to produce plutonium, for weapons grade material to support the nuclear arms race and to fuel civilian reactors, was satisfied by uranium fuelled breeder reactors. The Nixon Administration chose, on the advice of the Atomic Energy Authority to support fast breeder reactors, and to progressively close down research into other alternatives. 

Why was the Oak Ridge Molten Salt Reactor Experiment Closed Down?

Much pioneering research into Molten Salt Reactors MSR’s was done at Oak Ridge National Laboratory between 1965 and 1969 where an experimental 7.4MW MSR was run for the equivalent of 1.5 years using 239Pu, 235U and 233U as fuels, the latter having been bred from 232Th. It was an engineering test system using graphite as a moderator which was intended to prove the viability of the design.  For this reason the surrounding blanket of thorium, which would normally breed 233U, was omitted in favour of neutron measurements.
This research programme was shut down in the seventies since it was felt that there was no need to pursue two lines of research in the field of nuclear power generation. Research into the thorium fuel cycle was, at best, considered a distraction and had nothing to contribute to the serious issues of keeping ahead of the Soviets in the nuclear arms race, neither was it relevant to Admiral Rickover's programme for the development of the Light Water Reactor to power submarines.

At that time Alvin Weinberg, the Director of the laboratory was becoming concerned about waste generated by the uranium/plutonium fuel cycle.  Weinberg was fired by the Nixon Administration on the advice of Senator Chet Holifield in 1973 after 18 years as the lab's director because he continued to advocate increased nuclear safety and Molten Salt Reactors, instead of the Administration's chosen Liquid Metal Fast Breeder Reactor LMFBR) that the AEC's Director of the Reactor Division, Milton Shaw, was appointed to develop.  Weinberg also wanted to move the Laboratory towards environmental researchWeinberg's firing effectively halted development of the MSR, as it was virtually unknown by other nuclear labs and specialists. Theoretical research continues in China, Grenoble, Russia  and elsewhere.

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There Must be Some Disadvantages or Everyone Would be Doing This Already!

Wastes - “Energy from Thorium” say that you create far less waste and furthermore you can burn waste plutonium in an LFTR.
This view is supported by the UK’s National Nuclear Laboratory in its 2010 position paper  which states that even when you take into account the fact that starter materials like 235U and 239Pu are needed, modest benefits in radio toxicity are to be expected.

Some environmentalists like Eifion Rees say that thorium just creates different radioactive wastes but others like Baroness Bryony Worthington, a labour peer and ex-friends of the Earth campaigner, support the use of LFTR's.

Unproven Technology - The National Nuclear Laboratory’ 2010 position paper considers only water cooled reactors powered by solid thorium fuel and dismisses the thorium fuel cycle as “.....representing significant financial investment and risk without notable benefits” [over the uranium-plutonium cycle]. It further states that they “....do not believe it has a role to play in the UK context, other than its potential application for plutonium management...” by which they mean disposal. (To me this paper is very conservative and represents a view, firmly rooted in the existing nuclear power industry’s interest in maintaining the status quo).  The NNL has recently been asked by the UK government to report on the subject once again.  I have not been able to establish the details of their brief.

It’s true, however, that the technology is unproven on anything other than a demonstration scale. Many areas need further research , like the selection of materials, and their response to the conditions inside an LFTR.  The choice of waste treatment options, the handling of tritium, produced when lithium is used in the molten salt mixture, and the optimal size for thorium fuelled power stations all require detailed development. There are many technical challenges to be overcome but none are likely to be insurmountable within reasonable cost limits.

Complexity - For the LFTR designs currently being proposed you need to combine the reactor and a chemical processing plant on one site. Waste processing, whether batch or online, is an integral part of the process since without it neutron absorbing elements and isotopes are formed which poison the reactor, quickly reducing output to the point where an LFTR will not work. This adds to the degree of complexity of the installation but only to the same extent as is familiar in existing chemical plants. The Oak Ridge research showed that this plant would be very small since the waste quantities are not large. This article gives a good explanation of the chemical processing options that can be adopted for use with a Liquid Fluoride Thorium Reactor LFTR. 

It’s not Renewable Energy - Whilst there are many informed proponents of LFTR technology the same cannot yet be said of the opponents, who don’t appear to have caught up with it yet. The weirdest “anti” argument that I have found so far is that “such potentially easily constructed nuclear power plants are likely to be installed everywhere, so that even if they generate less waste, and less dangerous waste, the net result will be that there will be a lot more waste!”

Perhaps the opponents of nuclear energy think that renewable sources will be able to replace the world’s electricity needs currently being generated by burning fossil fuels, even though in my opinion most renewable sources are unsuitable for base load power generation.  Solar energy only works during the day, wind power only works when it’s windy and wave power needs waves and a coastline not too far away!  So far, all of these renewable options are only in use because of subsidies paid for by consumers in their electricity bills or taxes.  Although, renewables have disadvantages they do, nevertheless, have a place in the future of global energy supply, albeit not a dominant one.

Vested Interests – It’s always easier to maintain the status quo, even if  better options exist, than to boldly go in a new direction! Companies already working in the nuclear industry are committed to promoting their own products.  A decade ago France’s nuclear industry killed proposals for funding from Brussels for a project by Nobel laureate Carlo Rubbia at CERN (European Organization for Nuclear Research), although it must be said that a French group is still actively working on theoretical aspects of thorium powered MSR’s in Grenoble.

In Conclusion

Electricity generation from nuclear power does not generate greenhouse gases. (Don’t forget that thermal power stations burning fossil fuels typical throw away, as waste heat, 70% of the energy they consume, which is a major contribution to the increase of atmospheric greenhouse gases). Reliance on fossil fuels from politically unstable countries is neither an advisable nor a sustainable option.

Nuclear power generation is ideally suited to base load duties. If better, safer options exist than the current generation of Pressurised Water Reactors (PWR’s), based on the uranium/plutonium fuel cycle, we should be investing in them.

Critics say thorium powered fourth generation reactors are unproven technology, but if you never build any large scale plants, then they always will be.

Norway’s Aker Solutions has bought Professor Rubbia’s patent. It had hoped to build the first sub-critical reactor in the UK, but seems to be giving up on Britain and locking up a deal to build it in China instead,  where minds and wallets are more open. Fortunately the Chinese, who don’t have the heavy burden of a nuclear industry based on uranium technology on their shoulders, are taking the lead.

Thanks to Ken Pottinger of French news online for introducing the subject of thorium fuelled nuclear power to me.


Joe Bonometti's 55 minute, 2008 Google Tech Talk is full of additional detail.



Other posts about nuclear power in this blog

2 comments:

  1. Nicely written article and mind blowing to read about this technology!
    thank you

    ReplyDelete
  2. Glad you had the opportunity to hear about thorium - I think I learned of it a few years before this post, quite by accident, and now anyone I meet who listens to me for 10 minutes always asks the same question, "why aren't we using this!?" Since 2011 there's been ever-growing talk about thorium in the news, so with luck we'll start seeing progress soon...

    ReplyDelete