Research Paper no. 11 2007–08
Thorium in Australia
Greg Baker
Statistics and Mapping Section
17 September 2007
Contents
Executive summary
Introduction
Thorium
Sources of thorium
Thorium resources
Thorium as a nuclear fuel
The future of thorium in Australia
Conclusion
Glossary
Endnotes
- Thorium is a radioactive element that can be used in a new
generation of nuclear reactors as an alternative source of fuel for
the generation of electricity.
- A thorium-based fuel cycle is more proliferation resistant than
conventional uranium-based reactors though there is still a degree
of risk.
- A thorium-based fuel cycle is less accident prone and is more
energy efficient than conventional uranium-based reactors.
- Thorium-based fuel cycle waste products are not as long lived
as those from conventional nuclear reactors.
- Thorium is abundant in Australia.
- There are technical issues still needing resolution before a
thorium-based fuel cycle can become common.
- Even if the technical issues can be resolved there are still
residual environmental concerns in the mining, handling and storage
of radioactive materials.
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Introduction
Thorium is a
naturally-occurring radioactive element that can be used in a new
generation of nuclear reactors as an alternative source of fuel for
the generation of electricity.
Thorium has several advantages as a nuclear
fuel:
-
it produces less of the nuclear by-products
normally used to make nuclear weapons and less of the long-lived
radioactive products of conventional nuclear power
-
its use in suitable nuclear reactors can reduce
the hazard of nuclear accidents
-
unlike natural uranium, its energy content can
be used almost in its entirety, and
-
thorium ore minerals are abundantly available
in Australia.
There are, however, some technical issues to
be resolved before thorium can be considered as a fuel for
Australia s future. If these technical issues can be resolved,
residual environmental concerns of mining, handling and storage of
radioactive materials will still make the decision to use any
thorium-based fuel cycle a political one.
This research paper discusses thorium and the
implications of its use, particularly in the Australian
context.
Thorium is a naturally-occurring radioactive
element. [1] It was
discovered in 1828 by the Swedish chemist and mineralogist J ns
Jakob Berzelius who named the element after Thor, the Norse god of
thunder. [2] In 1898
Gerhard Carl Schmidt and Marie Curie independently found that
thorium was radioactive. [3]
In its natural state thorium is composed
almost entirely of an isotope called thorium-232. Isotopes of an
element, although chemically the same as each other, have
different nuclear structures. [4]
Thorium-232 has a half-life of
14 050 million years, meaning that half of any given mass
will decay disintegrate into other nuclear products in that time;
14 050 million years is over three times the age of the earth.
This means that thorium-232 is not particularly radioactive,
although its decay products are. From its natural state,
thorium-232 decays through a number of stages finishing with
lead-208, which is stable. [5]
Thorium is used for some industrial purposes,
including bringing the intense white colour to gas-lamp mantles.
However, its principal modern interest is as a nuclear fuel.
Thorium is found in small quantities in the
earth s upper crust where, at 6 10 parts per million, it is
about three times more abundant than uranium. [6]
The main source of thorium in Australia and
worldwide is the mineral monazite which is a reddish-brown
rare-earth phosphate mineral. [7] Monazite contains 8 10 per cent thorium.
[8] Other minerals
containing thorium include thorite (thorium silicate), a thorium
uranium mineral which is also an important ore of uranium and
thorianite which contains around 70 per cent thorium dioxide.
[9]
In Australia monazite is usually found as a
component of heavy mineral sand deposits. [10] Because there is no market for the
mineral, monazite is not extracted during mining for heavy mineral
sands but dispersed back through the original host material when a
mining site is returned to its agreed post-mining land use.
[11] This dispersal
of monazite is done to prevent concentrations of radioactivity in
rehabilitated mine sites. [12] However, in doing so, the thorium and rare earths
present in the monazite are negated as a resource as it is unlikely
to be economic to recover the dispersed monazite for its rare earth
and thorium content.
Because there has been little commercial
demand for thorium there are few detailed records on Australia s,
or the world s, thorium resources. [13]
However, Geoscience Australia estimates that
Australia s monazite resources amount to 5.2 million tonnes.
At an estimated average thorium content of 7 per cent,
this is calculated to mean thorium resources of around 364 000
tonnes from this source. In addition, Geoscience Australia notes
that the resources at Nolans Bore, 135 kilometres northwest of
Alice Springs, contain 60 600 tonnes of thorium dioxide
amountint to 53 300 tonnes of thorium; another deposit,
Toongi, 30 kilometres south of Dubbo in New South Wales
contains about 35 000 tonnes of thorium.
Summing these three figures yields an estimate
for Australia s total identified thorium resources of 452 300
tonnes which Geoscience Australia estimates are extractable at less
than US$80 per kilogram of thorium. [14]
Other countries with thorium resources include
India, Norway, the USA and Canada.
Table 1 shows estimates of world thorium
resources derived by Geoscience Australia. [15]
The identified resources in the table are
those resources considered to be extractable at less than
US$80 per kilogram. The figure for Australia is the Geoscience
Australia estimate discussed above. The remaining figures are from
the OECD s Nuclear Energy Agency (NEA) reproduced by Geoscience
Australia. [16]
Undiscovered resources are resources which are believed to exist
and to be exploitable using conventional mining techniques; they
have not yet been physically confirmed. Data for China and for
central and eastern Europe are not available. [17]
These figures show that Australian thorium
resources are significant on a world scale.
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Naturally-occurring thorium, thorium-232,
although radioactive, is not capable of sustaining a nuclear chain
reaction; the necessary basis for extracting energy from nuclear
fuel is a controlled, self-sustaining nuclear chain reaction.
Thorium-232 is, however, fertile. Being fertile means that
thorium is capable of being converted into a fissile
material, i.e. into a material that is capable of
sustaining a nuclear chain reaction.
This conversion process is relatively
straightforward. When the nucleus of a thorium-232 atom is
bombarded with neutrons, it passes relatively quickly through two
steps to produce uranium-233 which is fissile. [18]
To undertake this process and to produce a
useable fuel source, it is necessary to devise a source of
neutrons. This can be achieved by using neutrons from plutonium or
from enriched uranium or from both as they undergo fission in a
conventional reactor or in a fast breeder reactor, a
reactor which is designed to produce more fissile material than it
consumes. [19]
Fission is the process whereby large atoms split into smaller
atoms, releasing energy and subatomic particles in the process;
some of these particles are neutrons.
Another way to produce neutrons is to use a
device called a particle accelerator. When a heavy
metallic target such as lead is irradiated with high energy protons
(another type of subatomic particle) large numbers of neutrons are
produced.
The thorium fuel cycle can be either a
closed fuel cycle, or an open fuel cycle (also
known as a once-through fuel cycle). [20]
In a closed fuel cycle uranium-233 produced
from thorium-232 as outlined above, as well as other fissile
material in the spent fuel of a reactor are separated, and then
used as fuel in the same or in another reactor. In the first stage
in this process, uranium-233 is prepared as an almost pure isotope,
which can be separated by chemical means. [21] This chemical separation is possible
because the three elements involved in the conversion of
thorium-232 to uranium-233 thorium, protactinium and uranium have
different chemical properties; they will all be present after the
neutron bombardment of thorium-232. [22] The uranium-233 is then fabricated as
part of fuel assemblies for the second stage where a reactor uses
uranium-233 as a nuclear fuel. [23] The system is called closed because ultimately
the spent fuel from the power reactor needs to be re-processed.
In an open fuel cycle, or once-through fuel
cycle, of which there are several practical variations, thorium-232
is placed with the fissile materials uranium or plutonium within a
fuel assembly. The fission of the uranium or plutonium converts the
thorium-232 to uranium-233, which in turn fissions, sustaining the
process.
The other approach to creating neutrons to
bombard thorium-232 is to use a particle accelerator. Some people
within the nuclear industry consider the use of particle
accelerators as too expensive for the moment as a practical option
for the generation of slow neutrons. [24] Other researchers believe that this
has become a realistic option due to advances in computer and
accelerator technology and work on what are called accelerator
driven subcritical systems (ADS) is continuing in several
laboratories across the world. [25]
In an ADS, a stream of protons also subatomic
particles are fired at what is called a spallation target.
The spallation target is made from a material like lead or bismuth.
When struck by the protons, it releases large numbers of neutrons,
among other subatomic particles, which can be directed to strike
the thorium-232 fuel. The thorium-232 converts to uranium-233 which
fissions in situ aided by the neutron stream from the
accelerator. The advantage of this system, according to proponents,
is that because the reactor is subcritical (not self-sustaining),
it will simply stop if the accelerator is turned off. [26]
There have been many experiments in countries
including Germany, India, Japan, Russia, the United Kingdom and the
USA seeking ways in which thorium may be used as a nuclear fuel.
[27] These
experiments began soon after the Second World War and
thorium-fuelled reactors were trialled in the late 1970s and early
1980s. There are no commercial scale thorium reactors yet in
operation and thorium cannot be used directly in current generation
uranium-fuelled reactors. [28]
The future of thorium as a nuclear fuel in
Australia has been canvassed in several recent reports. These
include the House of Representatives Standing Committee on Industry
and Resources
Australia s uranium greenhouse friendly fuel for an energy hungry
world and the so-called Switkowski report Uranium
mining, processing and nuclear energy opportunities for
Australia? Within the context of the need to reduce
Australia s greenhouse gas emissions, these reports refer to the
advantages of thorium mentioned in the introduction above:
-
thorium produces less of the nuclear
by-products normally used to make nuclear weapons and less of the
long-lived radioactive products of conventional nuclear power
-
thorium s use in nuclear reactors can reduce
the hazard of nuclear accidents
-
thorium s energy content can be used almost in
its entirety and
-
thorium is in relative abundance in Australia.
[29]
As noted above, using thorium as a nuclear
fuel produces less of the nuclear by-products normally used to make
nuclear weapons and less long-lived nuclear waste.
The uranium-233 produced from thorium-232 has
a great advantage over uranium-235, the fuel of traditional nuclear
power reactors it does not produce plutonium which is the greatest
nuclear weapons proliferation risk. [30] In addition, the thorium fuel cycle
is proliferation resistant because of the presence of an
isotope of uranium, uranium-232, and its highly radioactive and
difficult-to-handle decay products. [31]
These advantages are true for thorium as a
fuel whichever technology is chosen. However accelerator driven
subcritical systems simply do not produce the plutonium-239 which
is used in nuclear weapons and only produces small quantities of
nuclear waste which needs storage for no more than 500 years. Using
thorium in conventional or fast breeder reactors reduces the amount
of weapons-useable material and reduces the amounts of very
long-life radioactive material. [32]
Thorium-based accelerator driven subcritical
systems can also be used to change highly radioactive waste from
conventional nuclear reactors into more benign and shorter-lived
radioisotopes. [33]
Using the thorium fuel cycle in conventional
critical reactors has many benefits (as discussed above) but it
does not reduce the risk of nuclear accidents.
However if the thorium fuel cycle is used in
an accelerator driven subcritical system the possibility of nuclear
accidents will be almost eliminated. An accelerator driven system
by definition is a subcritical nuclear reactor and will remain
operational as long as the neutrons from an external source are
injected into the reactor. [34] An ADS system can simply be switched off, taking
advantage of the subcritical nature of the thorium core. Such a
reactor cannot melt down; a meltdown is a situation where
the heat of a nuclear reaction cannot be contained and the reactor
core melts.
In addition, the thorium used in nuclear
reactors is used as the chemical thorium dioxide which at 3300
degrees Celsius has the highest melting point of any oxide. This
provides far better thermal and physical properties than the
uranium oxide used in conventional reactors. [35]
Depending on the fuel cycle used, the energy
content of thorium can be used almost in its entirety. Virtually
all natural thorium is thorium-232 and is potentially useable in a
reactor compared to 0.7 per cent of natural uranium.
[36]
The ores of thorium are in abundance in
Australia although they are geographically dispersed. With little
change to current sand mining practices, monazite can be readily
extracted for its thorium and rare earth mineral content, rather
than being discarded.
Not all technical problems have yet been
solved in the development of fuel cycles based on thorium. The
World Nuclear Association, echoed by Australia s Uranium
Information Centre, has highlighted four of these problems.
[37]
Firstly, it is difficult and expensive to
fabricate fuel for closed cycle thorium reactors. Uranium-233,
chemically separated from irradiated thorium, is highly radioactive
and hence hard to handle for fuel assembly fabrication. In
addition, separated uranium-233 is always contaminated with
uranium-232. Uranium-232 is radioactive, has a half life of
68.9 years and produces strong gamma emitters like
thallium-208 as decay products. [38]
Secondly, there are technical difficulties in
recycling thorium due to the high radioactivity of thorium-228
which is a decay product of the contaminant uranium-232. [39]
Thirdly, there is some nuclear proliferation
risk with uranium-233 if it can be separated.
And fourthly, there are technical problems in
reprocessing spent fuel from these reactors.
Were the technical difficulties to be
resolved, it is by no means clear that Australia s environmental
movement would accept a thorium-based nuclear future for Australia.
Two states New South Wales and Western Australia have current bans
on the mining of thorium and influential organisations such as the
Australian Conservation Foundation (ACF) are opposed to any nuclear
industry in Australia. [40] The ACF correctly points out that uranium-233 is still
subject to the same safeguard requirements as uranium-235, the
material used in conventional nuclear reactors, as is any uranium
or plutonium used to make neutrons for the thorium cycle. [41]
There are several advantages for Australia in
pursuing a thorium-based nuclear future in preference to the
conventional uranium-based reactors that are now central to the
nuclear and climate change debate.
However, with technical problems yet to be
resolved, the current relative abundance of uranium, and an
environmental movement opposed to any nuclear activities in
Australia, a thorium-based nuclear future does not appear likely in
the short to medium term. [42]
Back to top
accelerator driven subcritical
system See ADS.
ADS An accelerator driven
subcritical system. This is a subcritical reactor.
alpha decay Radioactive decay in which the nucleus of an atom emits
two protons and two neutrons this is identical to emitting a helium
nucleus.
anti-neutrino A sub-atomic
particle.
atom One of the building
blocks of matter. In simple terms an atom comprises a nucleus and a
number of electrons.
beta decay With beta decay,
within the nucleus a neutron spontaneously changes into a proton
which produces the new element and ejects an electron and another
sub-atomic particle called an anti-neutrino.
closed fuel cycle A nuclear
fuel cycle in which the nuclear fuel is re-processed after it
leaves the reactor.
electron A sub-atomic
particle.
element A substance which
cannot be changed into another substance by ordinary chemical
processes
fast breeder reactor A
reactor which is designed to produce more fissile material than it
consumes.
fertile A fertile element is
capable of being converted into fissile material.
fissile A fissile material is
one that is capable of sustaining a nuclear chain reaction.
gamma emission The radiation
produced during some radioactive decay.
half-life The half-life of a
radioactive element or isotope is the time that it takes for
exactly half its mass to decay to other isotopes.
isotope Isotopes of an
element, although chemically the same as each other, have different
nuclear structures.
mineral A naturally-occurring
homogeneous solid that has a definite chemical composition and a
highly ordered atomic structure.
mixed oxide fuel Nuclear fuel
which is a mixture of the oxides of several nuclear fuels including
uranium, plutonium and thorium.
monazite A reddish-brown
rare-earth phosphate mineral.
naturally-occurring element
An element found in nature and which has not been manufactured
using nuclear processes.
neutron A sub-atomic particle
that is in the nucleus of all atoms except hydrogen.
nuclear chain reaction A
controlled, self-sustaining nuclear chain reaction is the necessary
basis for extracting energy from nuclear fuel.
nucleus The core of an atom.
It contains protons and neutrons.
once-through fuel cycle See
open fuel cycle.
open fuel cycle A nuclear
fuel cycle in which the nuclear fuel is not re-processed after it
leaves the reactor.
particle accelerator A device
which accelerates charged particles such as protons and thus
increases their energy.
proliferation resistant A
process or product which is difficult to be used for the
manufacture of nuclear weapons.
protactinium-233 An isotope
of proactinium which is a decay product of thorium-233.
proton A sub-atomic particle
that is in the nucleus of all atoms.
radioactive decay A process
in which spontaneously and randomly the state of an atomic nucleus
is altered and gamma or nuclear particles are emitted.
radioactive element An
element that has an unstable atomic nucleus this sort of element
spontaneously and randomly alters the state of its atomic nucleus,
emitting sub-atomic particles in the process.
rare-earth mineral A group of
elements once thought rare and difficult to separate.
spallation target Material
that produces neutrons when struck by a stream of protons.
sub-atomic particles The
building blocks of atoms. There are many different sorts of
sub-atomic particle including the electron, the proton and the
neutron.
subcritical reactor A nuclear
reactor which is not self-sustaining.
thorium A naturally-occurring
radioactive element which can be used in nuclear reactors as an
alternative source of fuel for the generation of electricity.
thorium-232 This is the
naturally occurring form of the element thorium.
thorium-233 This isotope is
produced when thorium-232 is bombarded with slow neutrons.
uranium-232 A highly
radioactive contaminant of the process to produce uranium-233.
uranium-233 The fissile
material produced from the bombardment of thorium-232 with
neutrons.
uranium-235 The uranium
isotope used in conventional nuclear power reactors.
uranium-238 The uranium
isotope that forms the great bulk of naturally-occurring
uranium.
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Endnotes
[1]. In simple
terms, an element is a substance which cannot be changed into
another substance by ordinary chemical processes. Iron and lead,
for example, are elements. A naturally-occurring element
is found in nature and has not been manufactured using nuclear
processes. A radioactive element is an element that has an
unstable atomic nucleus this sort of element spontaneously and
randomly alters the state of its atomic nucleus, emitting
sub-atomic particles in the process. Sub-atomic particles are the
building blocks of atoms. There are many different sub-atomic
particles; those mentioned here are the electron, and the
proton and the neutron which in combination make
up an atomic nucleus.
[2]. James B Hedrick, Thorium , United States Geological
Survey at
http://minerals.usgs.gov/minerals/pubs/commodity/thorium/690798.pdf,
accessed 23 July 2007; and Uranium Information Centre,
Thorium , Briefing Paper, no. 67, UIC, May 2007,
http://www.uic.com.au/nip67.htm,
accessed 23 July 2007.
[4]. The number that is part of the isotope name here 232 is
the isotope s atomic mass number. This mass number is the sum of
the number of protons in the nucleus here 90 and the number of
neutrons in the nucleus here 142. The isotope thorium-228 also
occurs in the decay series of thorium-232, i.e. in the chain of
nuclear products produced as thorium-232 disintegrates. Most of
these are short-lived isotopes and hence more radioactive than
thorium-232; they are negligible in mass. A diagram of the decay
series follows in the next footnote. Thorium , World Nuclear
Association at http://www.world-nuclear.org/info/inf62.htm,
accessed 23 July 2007.
[5]. McGraw-Hill Encyclopedia of Science and
Technology, 9th edition, p. 414 and the web site http://environmentalchemistry.com/yogi/periodic.
Thorium-232 with an atomic mass number of 232 eventually decays to
lead-208 with an atomic mass number of 208.
[6]. Nuclear Energy Agency/Organisation of Economic
Co-operation and Development, Forty years of uranium resources,
production and demand in perspective: The Red Book
retrospective , NEA/OECD, Paris, 2006, p. 135.
[7]. A mineral is a naturally-occurring homogeneous solid
that has a definite chemical composition and a highly ordered
atomic structure. Rare-earth minerals are a group of elements once
thought rare; the term is probably now a misnomer. See
McGraw-Hill Encyclopedia of Science and Technology, 9th
edition, pp. 188 and 212.
[8]. Nuclear Energy Agency/Organisation of Economic
Co-operation and Development, loc. cit. Interestingly,
monazite contains significant amount of helium caused by the alpha
decay of thorium and uranium; the helium can be extracted by
heating. In alpha decay the nucleus of an atom emits two protons
and two neutrons this is identical to emitting a helium
nucleus.
[9]. McGraw-Hill Encyclopedia of Science and
Technology, 9th edition, p. 414; and US Department of Energy,
Argonne National Laboratory, Environmental Science Division,
Radiological and chemical fact sheets to support health risk
analyses for contaminated areas: thorium, August 2005,
http://www.ead.anl.gov/pub/doc/ANL_ContaminantFactSheets_All_070418.pdf,
accessed 30 July 2007.
[10]. Geoscience Australia, Australia s
identified mineral resources 2007, Geoscience Australia,
Canberra, 2007. These mineral sands are often found in placer
deposits which are accumulations of dense materials trapped by the
flow of water. Placer materials are dense materials that because of
their density fail to be carried along by water flow and are left
behind and concentrated in hollows and bends.
[11]. The minerals in mineral sands are extracted for their
titanium and zirconium content.
[12]. Geoscience Australia, loc. cit. Radiation is
an occupational health issue in the mineral sands industry and
heavy mineral sands production is managed under the Code of
Practice for Mining and Milling of Radioactive Ores. Current
performance data indicate that current radiation levels are well
below the recently set Commonwealth Radiation Protection
Code limit for occupational exposure.
[13]. Geoscience Australia, loc. cit.
[14]. Geoscience Australia, op. cit., pp 71 2. The
figure of US$80 per kilogram is conventionally taken as the cut-off
point for measuring the quantity of extractable resources of
uranium and thorium. It does not imply that extraction is economic
at that level because extraction is only economic if the market
price exceeds the extraction cost. In the case of thorium there is
no market price. Also Yanis Miezitis, Geoscience Australia,
personal communication, 31 August 2007 and 12 September
2007.
[15]. Geoscience Australia, op. cit., p.73 and
Yanis Miezitis, Geoscience Australia, personal communication,
31 August 2007. Other figures for thorium resources are at
U.S. Geological Survey (USGS), Thorium , Mineral Commodity
Summaries 2007, United States Government Printing Office,
Washington, 2007, pp. 170 1. The entire USGS publication is at
http://minerals.usgs.gov/minerals/pubs/mcs/2007/mcs2007.pdf,
accessed 30 July 2007; the thorium chapter can be viewed at
http://minerals.usgs.gov/minerals/pubs/commodity/thorium/thorimcs07.pdf,
accessed 30 July 2007. Note that estimates from different
sources vary because of different assumptions underlying their
compilation and different interpretations of the term reserves
.
[16]. Nuclear Energy Agency/Organisation of Economic
Co-operation and Development, Forty years of uranium resources,
production and demand in perspective: The Red Book
retrospective , NEA/OECD, Paris, 2006, p. 136 8.
[18]. Neutrons are sub-atomic particles typically found
within the nucleus of atoms. Outside the nucleus, free neutrons can
be fired at nuclear targets such as thorium-232 atoms. A slow
neutron has low energy. When bombarded with a slow neutron,
thorium-232 absorbs the neutron and hence becomes thorium-233.
Thorium-233 has a half life of about 22 minutes decaying into
protactinium-233. Protactinium-233 has a half-life of about
27 days decaying into uranium-233. Each of these radioactive
decays happens by a process called beta emission or
beta decay. With beta decay, within the nucleus a neutron
spontaneously changes into a proton which produces the new element
and ejects an electron and another sub-atomic particle called an
anti-neutrino. The resulting uranium-233 is fissile, i.e. is
capable of sustaining a nuclear chain reaction. Because of the
additional proton, the thorium has become protactinium which has 91
protons compared to thorium s 90 and the protactinium in turn
becomes uranium which has 92 protons.
[19]. The fissile isotope uranium-235 is not sufficiently
concentrated in uranium in its natural state for the uranium to be
useful as a fuel. The natural occurrence of about 0.7 per cent
uranium-235 needs to be increased enriched to around three per cent
uranium-235. See Ian Clark and Barry Cook, Uranium ,
Introduction to Australia s Minerals, vol. 5, Uranium
Information Centre, 2000, p. 12. Although the element
plutonium is found in very small trace amounts as the isotope
plutonium-244 in nature, plutonium is manufactured from uranium.
See http://environmentalchemistry.com/yogi/periodic/Pu.html,
accessed 2 August 2007. The thorium used in conventional
nuclear reactors is used in the form of mixed oxide fuel
where oxides of thorium and of uranium or plutonium are mixed in
forming the fuel assembly. S R Hashemi-Nezhad, University of
Sydney, personal communication, 4 September 2007.
[20]. International Atomic Energy Agency, Thorium fuel
cycle potential benefits and challenges, IAEA-TECDOC-1450,
IAEA, Vienna, May 2005, p. 10.
[21]. In practice the uranium-233 will not be pure and will
be contaminated with small amounts of uranium-232. Uranium-232 is
highly radioactive; its decay products such as thallium-208 and
bismuth-212 emit strong gamma radiation with very short half lives.
Uranium Information Centre, Thorium , Briefing Paper, no.
67, UIC, May 2007, http://www.uic.com.au/nip67.htm,
accessed 31 July 2007 and http://environmentalchemistry.com/yogi/periodic,
accessed 31 July 2007.
[22]. This process is in contrast to the enrichment of
uranium which is needed for conventional nuclear power reactors.
Enrichment is the process of concentrating particular isotopes of
the uranium element which have the same chemical properties as each
other and hence cannot be chemically separated. See also footnote
21.
[23]. Uranium Information Centre, Thorium , Briefing
Paper, no. 67, UIC, May 2007, http://www.uic.com.au/nip67.htm,
accessed 31 July 2007. Nuclear fuel formed into fuel
assemblies are commonly used to build a nuclear reactor core.
[24]. Mujid S Kazimi, Thorium fuel for nuclear energy ,
American Scientist, vol. 91, no. 5, September
October 2003, p. 408.
[25]. S R Hashemi-Nezhad, Accelerator driven subcritical
nuclear reactors for safe energy production and nuclear waste
incineration , Australian Physics, vol. 43, no. 3, 2006,
p. 91
[26]. S R Hashemi-Nezhad ibid. and Uranium Information
Centre, Thorium , Briefing Paper, no. 67, UIC,
May 2007, http://www.uic.com.au/nip67.htm,
accessed 31 July 2007. Conventional nuclear reactors
operate in a critical mode and need complex systems to
slow and stop the reaction.
[27]. Uranium Information Centre, Thorium, Briefing
Paper no. 67, May 2007, http://www.uic.com.au/nip67.htm,
accessed 31 July 2007. The main proponent of thorium
nuclear power technology is India which is pursuing the thorium
route principally because of its concerns for security of supply
for its nuclear fuel. Two of India s nuclear power reactors are
loaded with thorium fuel in order to improve their operation when
newly-started. India plans to use thorium-based fuel in four
reactors under construction.
[28]. Uranium Information Centre, Thorium, Briefing
Paper no. 67, May 2007, http://www.uic.com.au/nip67.htm,
accessed 13 september 2007 and Yanis Miezitis, Geoscience
Australia, personal communication 12 September 2007.
[29]. Australia, House of Representatives, Standing
Committee on Industry and Resources, Australia s uranium
greenhouse friendly fuel for an energy hungry world, 2006; and
Department of Prime Minister and Cabinet, Uranium mining,
processing and nuclear energy opportunities for Australia?,
Report to the Prime Minister by the Uranium Mining, Processing and
Nuclear Energy Review Taskforce, 2006.
[30]. The uranium-235 in traditional nuclear power reactors
is never pure and will be mixed with over 90 per cent
uranium-238 in the fuel rods made for traditional nuclear power
reactors. The uranium-238 itself is fertile. When exposed to the
neutron bombardment in a nuclear reactor, atoms of uranium-238 on
absorbing a neutron become uranium-239. This is a short-lived
isotope and decays with a half-life of about 23 minutes into
neptunium-239. This neptunium-239 with a half-life of 2.4 days,
decays in turn into plutonium-239. Plutonium-239 is highly
radioactive with a half-life of 24 110 years. It is this waste
plutonium-239 which presents the greatest nuclear weapons
proliferation risk. See the uranium, neptunium and plutonium pages
at http://environmentalchemistry.com/yogi/periodic,
accessed 30 July 2007. A good general discussion of this is at
Tim Dean, New age nuclear , Cosmos, issue no. 8, 2006, pp
44 5.
[31]. International Atomic Energy Agency, Thorium fuel
cycle potential benefits and challenges, IAEA-TECDOC-1450,
IAEA, Vienna, May 2005, pp. 79 84.
[32]. S R Hashemi-Nezhad, personal communication,
4 September 2007.
[33]. Tim Dean, op. cit., pp. 46 7.
[34]. S R Hashemi-Nezhad, Accelerator driven subcritical
nuclear reactors for safe energy production and nuclear waste
incineration , Australian Physics, vol. 43, no. 3, 2006,
p. 91
[35]. International Atomic Energy Agency, Thorium fuel
cycle potential benefits and challenges, IAEA-TECDOC-1450,
IAEA, Vienna, May 2005.
[36]. International Atomic Energy Agency, Thorium fuel
cycle potential benefits and challenges, IAEA-TECDOC-1450,
IAEA, Vienna, May 2005, p. 12; and World Nuclear Association,
Thorium at http://www.world-nuclear.org/info/inf62.htm,
accessed 23 July 2007. There are, of course, losses in
transforming this energy into electricity but this is true of any
energy source.
[42]. The opinion of the chief of the Australian Nuclear
Science and Technology Organisation (ANSTO), Dr Ziggy Switkowski,
is that this technology may be as far away as the middle of this
century. See the ABC Television
Lateline interview of Dr Switkowski by Tony Jones, 15 August
2007.