See also the Friends of the Earth web-page on thorium and WMD proliferation risks.
Summary
The use of thorium-232 as a reactor
fuel is sometimes suggested as a long-term energy source, partly because of its
relative abundance compared to uranium.
Some experience has been gained
with the use of thorium in power and research reactors – but far less
experience than has been gained with conventional uranium reactors. The Uranium
Information Centre (2004) states that: “Much development work is still
required before the thorium fuel cycle can be commercialised, and the effort
required seems unlikely while (or where) abundant uranium is available.”
According to the World Nuclear
Association (2006): “Problems include the high cost of fuel fabrication
due partly to the high radioactivity of U-233 which is always contaminated with
traces of U-232; the similar problems in recycling thorium due to highly
radioactive Th-228, some weapons proliferation risk of U-233; and the technical
problems (not yet satisfactorily solved) in reprocessing. Much development work
is still required before the thorium fuel cycle can be commercialised, and the
effort required seems unlikely while (or where) abundant uranium is
available.”
Thorium fuel cycles are promoted on
the grounds that they pose less of a proliferation risk compared to conventional
reactors. However, whether there is any significant non-proliferation advantage
depends on the design of the various thorium-based systems. No thorium system
would negate proliferation risks altogether (Friedman, 1997; Feiveson, 2001).
Neutron bombardment of thorium
(indirectly) produces uranium-233, a fissile material which can be used in
nuclear weapons (1 Significant Quantity of U-233 = 8kg).
The USA has successfully tested
weapons using uranium-233 cores, and India may have investigated the military
use of thorium/uranium-233 in addition to its civil applications.
The proliferation risk is
exacerbated with existing and proposed configurations involving uranium-233
separation from irradiated fuel. As the World Nuclear Association (2006) notes:
“Given a start with some other fissile material (U-235 or Pu-239), a breeding
cycle similar to but more efficient than that with U-238 and plutonium (in
slow-neutron reactors) can be set up. The Th-232 absorbs a neutron to become
Th-233 which normally decays to protactinium-233 and then U-233. The irradiated
fuel can then be unloaded from the reactor, the U-233 separated from the
thorium, and fed back into another reactor as part of a closed fuel cycle.”
(A research reactor in India
operates on U-233 fuel extracted from thorium which has been irradiated and
bred in another reactor.)
The possible use of highly enriched
uranium (HEU) or plutonium to initiate a thorium-232/uranium-233 reaction, or
proposed systems using thorium in conjunction with HEU or plutonium as fuel
present the risk of diversion of HEU or plutonium for weapons production.
Kang and von Hippel (2001) conclude
that “the proliferation resistance of thorium fuel cycles depends very
much upon how they are implemented”. For example, the co-production of
uranium-232 complicates weapons production but, as Kang and von Hippel note,
“just as it is possible to produce weapon-grade plutonium in low-burnup
fuel, it is also practical to use heavy-water reactors to produce U-233
containing only a few ppm of U-232 if the thorium is segregated in
“target” channels and discharged a few times more frequently than the
natural-uranium “driver” fuel.”
One proposed system is an
Accelerator Driven Systems (ADS) in which an accelerator produces a proton beam
which is targeted at target nuclei (e.g. lead, bismuth) to produce neutrons.
The neutrons can be directed to a subcritical reactor containing thorium. ADS
systems could reduce but not negate the proliferation risks.
References:
Feiveson,
Harold, 2001, “The Search for Proliferation-Resistant Nuclear Power”,
The Journal of the Federation of American Scientists, September/October 2001, Volume
54, Number 5, www.fas.org/faspir/2001/v54n5/nuclear.htm
Friedman,
John S., 1997, “More power to thorium?”, Bulletin of the Atomic
Scientists, Vol. 53, No.5, September/October
Kang,
Jungmin, and Frank N. von Hippel, 2001, “U-232 and the
Proliferation-Resistance of U-233 in Spent Fuel”, Science & Global
Security, Volume 9, pp 1-32, www.princeton.edu/~globsec/publications/pdf/9_1kang.pdf
Uranium
Information Centre, 2004, “Thorium”, Nuclear Issues Briefing Paper #
67.
World
Nuclear Association, 2006, “Thorium”, http://www.world-nuclear.org/information-library/current-and-future-generation/thorium.aspx
Thorium ‒ a better fuel for nuclear technology?
Dr. Rainer Moormann, ‘Thorium ‒ a better fuel for nuclear technology?’, Nuclear Monitor #858, 1 March 2018.
Dr. Moormann’s article is online at the Nuclear Monitor website.
Thor-bores and uro-sceptics: thorium’s friendly fire
Jim Green, 9 April
2015, ‘Thor-bores and uro-sceptics: thorium’s friendly fire’, Nuclear Monitor
#801, www.wiseinternational.org/nuclear-monitor/801/thor-bores-and-uro-sceptics-thoriums-friendly-fire
Many
Nuclear Monitor readers will be
familiar with the tiresome rhetoric of thorium enthusiasts − let’s call them
thor-bores. Their arguments have little merit but they refuse to go away.
Here’s
a thor-bore in full flight − a science journalist who should know better:
“Thorium is a superior nuclear fuel to uranium in almost every conceivable way … If there is such a thing as green nuclear power, thorium is it. … For one, a thorium-powered nuclear reactor can never undergo a meltdown. It just can’t. … Thorium is also thoroughly useless for making nuclear weapons. … But wait, there’s more. Thorium doesn’t only produce less waste, it can be used to consume existing waste.”1
Thankfully,
there is a healthy degree of scepticism about thorium, even among nuclear
industry insiders, experts and enthusiasts (other than the thor-bores
themselves, of course). Some of that ‘friendly fire’ is noted here.
Readiness
The
World Nuclear Association (WNA) notes that the commercialization of thorium
fuels faces some “significant hurdles in terms of building an economic
case to undertake the necessary development work.” The WNA states:
“A great deal
of testing, analysis and licensing and qualification work is required before
any thorium fuel can enter into service. This is expensive and will not
eventuate without a clear business case and government support. Also, uranium
is abundant and cheap and forms only a small part of the cost of nuclear
electricity generation, so there are no real incentives for investment in a new
fuel type that may save uranium resources.
“Other
impediments to the development of thorium fuel cycle are the higher cost of
fuel fabrication and the cost of reprocessing to provide the fissile plutonium
driver material. The high cost of fuel fabrication (for solid fuel) is due
partly to the high level of radioactivity that builds up in U-233 chemically
separated from the irradiated thorium fuel. Separated U-233 is always
contaminated with traces of U-232 which decays (with a 69-year half-life) to
daughter nuclides such as thallium-208 that are high-energy gamma emitters.
Although this confers proliferation resistance to the fuel cycle by making
U-233 hard to handle and easy to detect, it results in increased costs. There
are similar problems in recycling thorium itself due to highly radioactive
Th-228 (an alpha emitter with two-year half life) present.”2
A
2012 report by the UK National Nuclear Laboratory states:
“NNL has
assessed the Technology Readiness Levels (TRLs) of the thorium fuel cycle. For
all of the system options more work is needed at the fundamental level to
establish the basic knowledge and understanding. Thorium reprocessing and waste
management are poorly understood. The thorium fuel cycle cannot be considered
to be mature in any area.”3
Fiona
Rayment from the UK National Nuclear Laboratory states:
“It is
conceivable that thorium could be introduced in current generation reactors
within about 15 years, if there was a clear economic benefit to utilities. This
would be a once-through fuel cycle that would partly realise the strategic
benefits of thorium.
“To obtain
the full strategic benefit of the thorium fuel cycle would require recycle, for
which the technological development timescale is longer, probably 25 to 30
years.
“To develop
radical new reactor designs, specifically designed around thorium, would take
at least 30 years. It will therefore be some time before the thorium fuel cycle
can realistically be expected to make a significant contribution to emissions
reductions targets.”4
Thorium is no
‘silver bullet’
Do
thorium reactors potentially offer significant advantages compared to
conventional uranium reactors?
Nuclear
physicist Prof. George Dracoulis states: “Some of the rhetoric associated
with thorium gives the impression that thorium is, somehow, magical. In reality
it isn’t.”5
The
UK National Nuclear Laboratory report argues that thorium has “theoretical
advantages regarding sustainability, reducing radiotoxicity and reducing proliferation
risk” but that “while there is some justification for these benefits,
they are often over stated.” The report further states that the purported
benefits “have yet to be demonstrated or substantiated, particularly in a
commercial or regulatory environment.”3
The
UK National Nuclear Laboratory report is sceptical about safety claims:
“Thorium
fuelled reactors have already been advocated as being inherently safer than
LWRs [light water reactors], but the basis of these claims is not sufficiently
substantiated and will not be for many years, if at all.”3
False distinction
Thor-bores
posit a sharp distinction between thorium and uranium. But there is little to
distinguish the two. A much more important distinction is between conventional
reactor technology and some ‘Generation IV’ concepts − in particular, those
based on repeated (or continuous) fuel recycling and the ‘breeding’ of fissile
isotopes from fertile isotopes (Th-232>U-233 or U-238>Pu-239).
A
report by the Idaho National Laboratory states:
“For fuel
type, either uranium-based or thorium-based, it is only in the case of
continuous recycle where these two fuel types exhibit different
characteristics, and it is important to emphasize that this difference only
exists for a fissile breeder strategy. The comparison between the thorium/U-233
and uranium/Pu-239 option shows that the thorium option would have lower, but
probably not significantly lower, TRU [transuranic waste] inventory and
disposal requirements, both having essentially equivalent proliferation risks.
“For these
reasons, the choice between uranium-based fuel and thorium-based fuels is seen
basically as one of preference, with no fundamental difference in addressing
the nuclear power issues.
“Since no
infrastructure currently exists in the U.S. for thorium-based fuels, and
processing of thorium-based fuels is at a lower level of technical maturity
when compared to processing of uranium-based fuels, costs and RD&D
requirements for using thorium are anticipated to be higher.”7
George
Dracoulis takes issue with the “particularly silly claim” by a
science journalist (and many others) that almost all the thorium is usable as
fuel compared to just 0.7% of uranium (i.e. uranium-235), and that thorium can
therefore power civilization for millennia. Dracoulis states:
“In fact, in
that sense, none of the thorium is usable since it is not fissile. The
comparison should be with the analogous fertile isotope uranium-238, which
makes up nearly 100% of natural uranium. If you wanted to go that way (breeding
that is), there is already enough uranium-238 to ‘power civilization for
millennia’.”5
Some
Generation IV concepts promise major advantages, such as the potential to use
long-lived nuclear waste and weapons-usable material (esp. plutonium) as reactor
fuel. On the other hand, Generation IV concepts are generally those that face
the greatest technical challenges and are the furthest away from commercial
deployment; and they will gobble up a great deal of R&D funding before they
gobble up any waste or weapons material.
Moreover,
uranium/plutonium fast reactor technology might more accurately be described as
failed Generation I technology. The first reactor to produce electricity − the
EBR-I fast reactor in the US, a.k.a. Zinn’s Infernal Pile − suffered a partial
fuel meltdown in 1955. The subsequent history of fast reactors has largely been
one of extremely expensive, underperforming and accident-prone reactors which
have contributed far more to WMD proliferation problems than to the resolution
of those problems.
Most
importantly, whether Generation IV concepts deliver on their potential depends
on a myriad of factors − not just the resolution of technical challenges.
India’s fast reactor / thorium program illustrates how badly things can go
wrong, and it illustrates problems that can’t be solved with technical
innovation. John Carlson, a nuclear advocate and former Director-General of the
Australian Safeguards and Non-Proliferation Office, writes:
“India has a
plan to produce [weapons-grade] plutonium in fast breeder reactors for use as
driver fuel in thorium reactors. This is problematic on non-proliferation and
nuclear security grounds. Pakistan believes the real purpose of the fast
breeder program is to produce plutonium for weapons (so this plan raises
tensions between the two countries); and transport and use of weapons-grade
plutonium in civil reactors presents a serious terrorism risk (weapons-grade
material would be a priority target for seizure by terrorists).”8
Generation
IV thorium concepts such as molten salt reactors (MSR) have a lengthy,
uncertain R&D road ahead of them − notwithstanding the fact that there is
some previous R&D to build upon.4,9
Kirk
Sorensen, founder of a US firm which aims to build a demonstration ‘liquid
fluoride thorium reactor’ (a type of MSR), notes that “several technical
hurdles” confront thorium-fuelled MSRs, including materials corrosion,
reactor control and in-line processing of the fuel.4
George
Dracoulis writes:
“MSRs are not
currently available at an industrial scale, but test reactors with different
configurations have operated for extended periods in the past. But there are a
number of technical challenges that have been encountered along the way. One
such challenge is that the hot beryllium and lithium “salts” – in
which the fuel and heavy wastes are dissolved – are highly reactive and
corrosive. Building a large-scale system that can operate reliably for decades
is non-trivial. That said, many of the components have been the subject of
extensive research programs.”10
Weapons
proliferation
Claims
that thorium reactors would be proliferation-resistant or proliferation-proof
do not stand up to scrutiny.11 Irradiation of thorium-232 produces
uranium-233, which can be and has been used in nuclear weapons.
The
World Nuclear Association states:
“The USA
produced about 2 tonnes of U-233 from thorium during the ‘Cold War’, at various
levels of chemical and isotopic purity, in plutonium production reactors. It is
possible to use U-233 in a nuclear weapon, and in 1955 the USA detonated a
device with a plutonium-U-233 composite pit, in Operation Teapot. The explosive
yield was less than anticipated, at 22 kilotons. In 1998 India detonated a very
small device based on U-233 called Shakti V.”2
According
to Assoc. Prof. Nigel Marks, both the US and the USSR tested uranium-233 bombs
in 1955.6
Uranium-233
is contaminated with uranium-232 but there are ways around that problem. Kang
and von Hippel note:
“[J]ust as it
is possible to produce weapon-grade plutonium in low-burnup fuel, it is also
practical to use heavy-water reactors to produce U-233 containing only a few
ppm of U-232 if the thorium is segregated in “target” channels and
discharged a few times more frequently than the natural-uranium
“driver” fuel.”12
John
Carlson discusses the proliferation risks associated with thorium:
“The thorium
fuel cycle has similarities to the fast neutron fuel cycle – it depends on
breeding fissile material (U-233) in the reactor, and reprocessing to recover
this fissile material for recycle. …
“Proponents
argue that the thorium fuel cycle is proliferation resistant because it does
not produce plutonium. Proponents claim that it is not practicable to use
U-233 for nuclear weapons.
“There is no
doubt that use of U-233 for nuclear weapons would present significant technical
difficulties, due to the high gamma radiation and heat output arising from
decay of U-232 which is unavoidably produced with U-233. Heat levels would
become excessive within a few weeks, degrading the high explosive and electronic
components of a weapon and making use of U‑233 impracticable for stockpiled
weapons. However, it would be possible to develop strategies to deal with these
drawbacks, e.g. designing weapons where the fissile “pit” (the core
of the nuclear weapon) is not inserted until required, and where ongoing
production and treatment of U-233 allows for pits to be continually replaced.
This might not be practical for a large arsenal, but could certainly be done on
a small scale.
“In addition,
there are other considerations. A thorium reactor requires initial core fuel –
LEU or plutonium – until it reaches the point where it is producing sufficient
U-233 for self-sustainability, so the cycle is not entirely free of issues
applying to the uranium fuel cycle (i.e. requirement for enrichment or
reprocessing). Further, while the thorium cycle can be self-sustaining on
produced U‑233, it is much more efficient if the U-233 is supplemented by
additional “driver” fuel, such as LEU or plutonium. For example,
India, which has spent some decades developing a comprehensive thorium fuel
cycle concept, is proposing production of weapons grade plutonium in fast
breeder reactors specifically for use as driver fuel for thorium reactors. This
approach has obvious problems in terms of proliferation and terrorism risks.
“A concept
for a liquid fuel thorium reactor is under consideration (in which the
thorium/uranium fuel would be dissolved in molten fluoride salts), which would
avoid the need for reprocessing to separate U-233. If it proceeds, this concept
would have non-proliferation advantages.
“Finally, it
cannot be excluded that a thorium reactor – as in the case of other reactors –
could be used for plutonium production through irradiation of uranium targets.
“Arguments
that the thorium fuel cycle is inherently proliferation resistant are
overstated. In some circumstances the thorium cycle could involve significant
proliferation risks.”13
Sometimes
thor-bores posit conspiracy theories. Former International Atomic Energy Agency
Director-General Hans Blix said “it is almost impossible to make a bomb
out of thorium” and thorium is being held back by the “vested
interests” of the uranium-based nuclear industry.14
But
Julian Kelly from Thor Energy, a Norwegian company developing and testing thorium-plutonium
fuels for use in commercial light water reactors, states:
“Conspiracy
theories about funding denials for thorium work are for the entertainment
sector. A greater risk is that there will be a classic R&D bubble [that]
divides R&D effort and investment into fragmented camps and feifdoms.”4
Thor-bores and
uro-sceptics
Might
the considered opinions of nuclear insiders, experts and enthusiasts help to
shut the thor-bores up? Perhaps not − critics are dismissed with claims that
they have ideological or financial connections to the vested interests of the
uranium-based nuclear industry, or they are dismissed with claims that they are
ideologically opposed to all things nuclear. But we live in hope.
Thor-bores
do serve one useful purpose − they sometimes serve up pointed criticisms of the
uranium fuel cycle. In other words, some thor-bores are uro-sceptics. For
example, thorium enthusiast and former Shell executive John Hofmeister states:
“The days of
nuclear power based upon uranium-based fission are coming to a close because
the fear of nuclear proliferation, the reality of nuclear waste and the difficulty
of managing it have proven too difficult over time.”15
References:
1.
Tim Dean, 16 March 2011, ‘The greener nuclear alternative’,
www.abc.net.au/unleashed/45178.html
2.
www.world-nuclear.org/info/Current-and-Future-Generation/Thorium/
3.
UK National Nuclear Laboratory Ltd., 5 March 2012, ‘Comparison of thorium and
uranium fuel cycles’,
www.decc.gov.uk/assets/decc/11/meeting-energy-demand/nuclear/6300-comparison-fuel-cycles.pdf
4.
Stephen Harris, 9 Jan 2014, ‘Your questions answered: thorium-powered nuclear’,
www.theengineer.co.uk/energy-and-environment/in-depth/your-questions-answered-thorium-powered-nuclear/1017776.article
5.
George Dracoulis, 5 Aug 2011, ‘Thorium is no silver bullet when it comes to
nuclear energy, but it could play a role’, http://theconversation.com/thorium-is-no-silver-bullet-when-it-comes-to-nuclear-energy-but-it-could-play-a-role-1842
6.
Nigel Marks, 2 March 2015, ‘Should Australia consider thorium
nuclear power?’,
http://theconversation.com/should-australia-consider-thorium-nuclear-power-37850
7.
Idaho National Laboratory, Sept 2009, ‘AFCI Options Study’, INL/EXT-10-17639,
www.inl.gov/technicalpublications/Documents/4480296.pdf
8.
John Carlson, 2014, submission to Joint Standing Committee on Treaties,
Parliament of Australia, www.aph.gov.au/DocumentStore.ashx?id=79a1a29e-5691-4299-8923-06e633780d4b&subId=301365
9.
Oliver Tickell, August/September 2012, ‘Thorium: Not ‘green’, not ‘viable’, and
not likely’, www.no2nuclearpower.org.uk/nuclearnews/NuClearNewsNo43.pdf
10.
George Dracoulis, 19 Dec 2011, ‘Thoughts from a thorium ‘symposium”,
http://theconversation.com/thoughts-from-a-thorium-symposium-4545
11.
www.foe.org.au/anti-nuclear/issues/nfc/power-weapons/thorium
12.
Jungmin Kang and Frank N. von Hippel, 2001, “U-232 and the Proliferation-Resistance
of U-233 in Spent Fuel”, Science
& Global Security, Volume 9, pp.1-32,
www.princeton.edu/sgs/publications/sgs/pdf/9_1kang.pdf
13.
John Carlson, 2009, ‘Introduction to the Concept of Proliferation Resistance’,
www.foe.org.au/sites/default/files/Carlson%20ASNO%20ICNND%20Prolif%20Resistance.doc
14.
Herman Trabish, 10 Dec 2013, ‘Thorium Reactors: Nuclear Redemption or Nuclear
Hazard?’,
http://theenergycollective.com/hermantrabish/314771/thorium-reactors-nuclear-redemption-or-nuclear-hazard
15. Pia Akerman, 7 Oct 2013, ‘Ex-Shell boss issues nuclear call’, The Australian, www.theaustralian.com.au/national-affairs/policy/ex-shell-boss-issues-nuclear-call/story-e6frg6xf-1226733858032
A thought for thorium
Nuclear Engineering International, 03 November 2009
www.neimagazine.com/story.asp?sectionCode=76&storyCode=2054564
The question of thorium fuel comes up every so often, says [Albert Machiels, senior technical executive at the USA’s Electric Power Research Institute]. “I really cannot claim that there is a great interest in thorium fuel – it is more a matter of curiosity. …
Experts disagree about whether thorium fuel is more proliferation-resistant than uranium. …
Many in the industry remain sceptical with regard to thorium. Now that uranium infrastructure is in place, developing a thorium fuel cycle is a ‘big risk,’ ‘unnecessary’ and a ‘distraction,’ according to some in the industry.
I put the question to Thorium Power; if thorium fuel is so good why aren’t we using it? Their response:
“Essentially the answer is because the nuclear industry started using UO2 on a large scale first and they’ve had 50 years to improve it and become comfortable with it. Due to a highly conservative nature of nuclear utilities (‘why change something that works just fine’), there has been little incentive for a commercial utility to switch from UO2 fuels even though ThO2-based fuels have many advantages.”
For this reason, if thorium fuel is going to take off it will need to be introduced in light water reactors first, notwithstanding the interesting reactor concepts currently being developed that use thorium. In accelerator-driven systems, or ADS, a particle accelerator knocks neutrons off a heavy element such as mercury, and those neutrons cause thorium to breed fissile uranium- 233. In molten salt reactors, thorium dissolved in a 650°C fluoride salt coolant breeds uranium-233, which undergoes fission.
“ADS and breeder reactors, such as molten-salt reactors, are so far in the future that if thorium has to wait for one of those developments it’s not going to happen. The point of entry must be the existing infrastructure, at least for the United States,” Machiels says.
Comparison of thorium and uranium fuel cycles
UK National Nuclear Laboratory Ltd.
A report prepared for and on behalf of Department of Energy and Climate Change
Issue 5, 5 Mar 2012
http://www.decc.gov.uk/assets/decc/11/meeting-energy-demand/nuclear/6300-comparison-fuel-cycles.pdf
EXECUTIVE
SUMMARY
The UK
National Nuclear Laboratory has been contracted by the Department for Energy
and Climate Change (DECC) to review and assess the relevance to the UK of the
advanced reactor systems currently being developed internationally. Part of the
task specification relates to comparison of the thorium and uranium fuel
cycles. Worldwide, there has for a long time been a sustained interest in the
thorium fuel cycle and presently there are several major research initiatives
which are either focused specifically on the thorium fuel cycle or on systems
which use thorium as the fertile seed instead of U-238. Currently in the UK,
the thorium fuel cycle is not an option that is being pursued commercially and
it is important for DECC to understand why this is the case and whether there
is a valid argument for adopting a different position in the future.
NNL has
recently published a position paper on thorium [1] which attempts to take a
balanced view of the relative advantages and disadvantages of the thorium fuel
cycle. Thorium has theoretical advantages regarding sustainability, reducing
radiotoxicity and reducing proliferation risk. NNL’s position paper finds that
while there is some justification for these benefits, they are often over
stated.
The value
of using thorium fuel for plutonium disposition would need to be assessed
against high level issues concerning the importance of maintaining high
standards of safety, security and protection against proliferation, as well as
meeting other essential strategic goals related to maintaining flexibility in
the fuel cycle, optimising waste arisings and economic competitiveness. It is
important that the UK should be very clear as to what the overall objectives
should be and the timescales for achieving these objectives.
Overall,
the conclusion is reached that the thorium fuel cycle at best has only limited
relevance to the UK as a possible alternative plutonium disposition strategy
and as a possible strategic option in the very long term for any follow-up
reactor construction programme after LWR new build. Nevertheless, it is
important to recognise that world-wide there remains interest in thorium fuel
cycles and as this is not likely to diminish in the near future. It may
therefore be judicious for the UK to maintain a low level of engagement in
thorium fuel cycle R&D by involvement in international collaborative
research activities. This will enable the UK to keep up with developments,
comment from a position of knowledge and to some extent influence the direction
of research. Participation will also ensure that the UK is more ready to
respond if changes in technology or market forces bring the thorium fuel cycle
more to the fore.