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Our expert panel answers
your questions on thorium-
fuelled fission reactors.
Stephen Harris reports
T horium is increasingly being promoted as an alternative fuel to
uranium in civil nuclear fission reactors. Proponents argue it’s
safer, more abundant and much harder to weaponise. But the
most significant development of thorium-fuelled reactors at Oak
Ridge National Laboratory in the US was cancelled in the 1970s and
the technology would need large amounts of investment to continue
readying it for commercial use.
For our latest reader Q&A, we put your questions to a panel of
n Julian Kelly, chief technology officer for Thor Energy, a Norwegian
firm developing and testing thorium-plutonium (Th-MOX) fuels for
use in commercial light water reactors (LWRs);
n David Martin, deputy director of research at the Weinberg
Foundation, a not-for-profit thorium lobby group;
n Fiona Rayment, director of fuel cycle solutions at the UK’s National
Nuclear Laboratory (NNL);
n Kirk Sorensen, founder of US firm Flibe Energy, which aims to
build a demonstration liquid-thorium-fuelled reactor (LFTR).
Old idea: Thorium research
dates back to the 1960s.
removal and high thermal conversion efficiency achieved at low
pressures. That final attribute is unique among reactors in this class.
The disadvantages are a small and aged base of scientists and
engineers who have actual experience in the technology, regulatory
challenges that will be faced to adapt solid-fuel reactor regulations
around liquid-fuel technology, the production of tritium in the salt
and its containment, and the challenge of developing a materials
database to support 30–60 year licensing of this class of reactors.
n What are the advantages and disadvantages of thorium-fuelled
Fiona Rayment: The main advantage is that
reactors over other proposed next-generation
the use of thorium is a potential strategic
The use of thorium alternative to using uranium/plutonium, and so
David Martin: First, it is essential to
distinguish between thorium fuel and
is a potential strategic could be energy additional contributor to fuel cycle
future reserves. The thorium
advanced reactors. In practice, most current
also generates much lower quantities of highly
and future reactors could be fuelled by
alternative to using
radioactive ‘transuranic’ materials, which are
thorium-based fuel, but only certain reactors
uranium/plutonium generally viewed as waste. Under some
are able to fully exploit thorium’s potential. The
circumstances, it is predicted that the thorium
two most promising thorium-fuelled reactors
fuel cycle could give an economic benefit, although this remains to
are high-temperature reactors (HTRs) and molten salt
be proven in practice. The main disadvantages are that thorium (in
the form of Th-232) is only fertile, not fissile and converting the
Thorium’s high melting point makes it ideally suited to HTRs [but]
thorium to fissile uranium-233 involves a neutron capture that is
MSRs offer a step-change in fuel efficiency and inherent safety.
time-consuming and expensive to implement. Another disadvantage
Liquid fluoride thorium reactors [a type of MSR] would breed the
is that utilising thorium will involve the development and
fissile isotope U233 and would automatically ‘burn up’ their own
deployment of new fuel-cycle technology, which has to compete with
wastes, producing minimal long-lived radioactive waste.
the established uranium fuel cycle. While it is true that using thorium
produces only trace amounts of plutonium, it does produce very
Kirk Sorensen: The advantages of LFTRs are the potential for much
high-quality fissile material that is a significant proliferation issue,
greater use fraction of fuel, the elimination of the need to fabricate
as is the case with the conventional uranium/plutonium fuel cycle.
solid-fuel elements, a completely passive approach to decay heat
“ 32 | theEnGineeR | DECEMBER 2013