After Fukushima, the nuclear industry is facing some serious problems. Some are simply plugging on ahead, but adding promises that they will upgrade existing reactor safety and operations, but others are looking to new technology. High on the list of new ideas is the use of thorium as a new fuel, with one favourite being the molten flouride salt thorium reactor. This allegedly will generate fewer wastes and might even be able to burn some of them up.
The attraction of thorium is that there is three times more of it in the world than uranium, but its disadvantage, at least as a reactor fuel, is that it is not fissile. You have to supply neutrons- the options being to use a particle accelerator as a source or to use uranium/plutonium fission. One idea is to have a blanket of thorium around a plutonium core. But you could also mix them up, possibly using this mix as a fuel in conventional reactors, or dissolve them in molten form- as in the liquid fluoride molten salt concept, with the liquid acting as both fuel and coolant. Doing it all in one reactor would be ideal- then, arguably, there would be less risk of illegal diversion of plutonium, or the production of weapons material.
India has been looking at thorium for some while, since, as a non signatory to the Nuclear Proliferation Treaty, it has faced problems importing uranium for its nuclear programme- whereas it has plenty of thorium. But they have approached it in a different way.
WNN reported that ‘The long-term goal of India’s nuclear programme has been to develop an advanced heavy-water thorium cycle. The first stage of this employs the pressurized heavy-water reactors and light water reactors, to produce plutonium. Stage two uses fast neutron reactors to burn the plutonium and breed uranium-233 from locally mined thorium. The blanket around the core will have uranium as well as thorium, so that further plutonium is produced as well. In stage three, AHWRs burn the uranium-233 from stage two with plutonium and thorium, getting about two thirds of their power from the thorium.’
Pretty complicated then, with several stages.
However , earlier this year, but before Fukushima, China announced that it would be developing a molten fluoride salt thorium system. Whether that, and China’s High Temperature helium cooled Pebble Bed modular reactor project, survived the post Fukushima review of nuclear policy remains to be seen- all new projects were temporarily halted.
The UK nuclear industry does not seem very interested in thorium,- it’s seen as a very long shot. Instead it is pinning its hopes for expansion on upgrades of the conventional pressurised water reactor- the French EPR and the US AP1000, even though neither of these have yet been built or operated yet.
A report from the UK’s National Nuclear Labs (NNL), based at Sellafield, was pretty dismissive of the thorium option- it would take years to develop land there weren’t many obvious benefits, given that uranium was plentiful.
NNL estimated that it would be likely to take ’10 to 15 years of concerted R&D effort and investment before the Thorium fuel cycle could be established in current reactors and much longer for any future reactor systems’. It went on ‘Thorium fuel concepts which require first the construction of new reactor types (such as High Temperature Reactor (HTR), fast reactors and Accelerator Driven Systems (ADS)) are regarded as viable only in the much longer term (of the order of 40+ years minimum)’.
What about the thorium breeder concept? NNL says ‘The use of thorium in place of U-238 as a fertile material in a once-through fuel …only yields a very small benefit over the conventional U-Pu fuel cycle. For example it is estimated that the approach of using seed-blanket assemblies (the blanket being the surrounding fertile thorium material) in a once-through thorium cycle in PWRs, will only reduce uranium ore demand by 10%. This is considered too marginal to justify investment in the thorium cycle on its own.’
And on the alleged avoidance or reduction of proliferation risks NNL says ‘Contrary to that which many proponents of thorium claim, U-233 should be regarded as posing a definite proliferation risk. For a thorium fuel cycle which falls short of a breeding cycle, uranium fuel would always be needed to supplement the fissile material and there will always be significant (though reduced) plutonium production’.
On the economics, NNL says that ‘while economic benefits are theoretically achievable by using thorium fuels, in current market conditions the position is marginal and insufficient to justify major investment. There is only a very weak technical basis for claims that thorium concepts using seed-blanket PWR cores will be economically advantageous. The only exception is in a postulated market environment of restricted uranium ore availability and thus very high uranium prices. This is not considered very likely for the foreseeable future.’
It’s not totally dismissive though. It says that ‘claims that thorium fuels give a reduction in radiotoxicity are justified. However, caution is required because many such claims cite studies based on a self-sustaining thorium cycle in equilibrium. More realistic studies which take account of the effect of U-235 or Pu-239 seed fuels required to breed the U-233 suggest the benefits are more modest. NNL’s view is therefore that thorium fuel cycles are likely to offer modest reductions in radiotoxicity. It is considered that the realistic benefits are likely to be too marginal to justify investment in the thorium fuel cycle’.
So there is some faint praise, but otherwise it’s a pretty damning review. Moving to perhaps even more exotic ideas, some see sub-critical particle accelerator driven systems (‘ADS’) as being useful, in that they could also possibly transmute some nuclear wastes, but that too is seen as a long shot option. A 2002 OECD/NEA study noted that ADS would require ‘fuel cycles with multiple recycling of the fuel and very low fuel losses’ and concluded that ‘the full potential of a transmutation system can be exploited only if the system is utilised for a minimum time period of about a hundred years’.www.oecd-nea.org/ndd/reports/2002/nea3109.html
And more recently UK Energy Minister Charles Hendry has noted that ‘As yet, industry has not indicated that they would be looking to develop and deploy sub-critical nuclear reactor designs in the UK in the near term future’.
Overall then it doesn’t look too good for thorium based systems, at least in the UK. Some work is going on in the USA on ADS under the Generation IV programme. For example, Aker Solutions, is developing a subcritical 600MWe fast neutron reactor which sustains a chain reaction in thorium and MOX fuel by using an accelerator to shoot a beam of protons into the molten lead coolant. The theory is that if anything went wrong the beam could be shut down instantly, halting fission. It’s a scaled-down version of Rubbia’s Energy Amplifier idea, developed as a concept at CERN some years ago, but with a smaller, cheaper, accelerator. But that means it runs closer to criticality- with safety implications.
There is also some US work on high temperature / fast neutron reactors, which could use thorium, with a degree of waste burn up possibly being achieved. Some novel mini-reactors are also being developed. But in terms of utility scale projects, it seems that the US programme is some decades away from a practical commercial reactor. That will surely also be true of the Chinese programme- although small prototypes may emerge before then, a 20 year timeframe was mentioned. But a 10MW Japanese Fuju project is claimed to be likely to be ready within 5 years.
Basically, possible fast track break throughs like this aside, for the moment we are stuck with what we have got- uranium pressurised water reactors.
For more optimistic views, see:
www.itheo.org(http://www.itheo.org) and www.thoriumenergy.org
There is clearly a significant lobby in the USA, including, notably, US climate scientist Dr. James Hansen, and there has been some positive UK media coverage, including from the Guardian: http://www.guardian.co.uk/environment/2009/jul/13/manchester-report-nuclear
But it probably didn’t help the case for thorium that British National Party leader Nick Griffin MEP, backed the liquid fluoride thorium concept strongly in a recent speech to the Europarliament. http://www.eutimes.net/2011/04/nick-griffin-leaves-climate-change-eurocrats-speechless/