One reason reprocessing thorium fuel cycles haven’t been successful is that uranium-232 (U-232) is created along with uranium-233. U-232, which has a half-life of about 70 years, is extremely radioactive and is therefore very dangerous in small quantities:
Thorium Fuel: No Panacea for Nuclear Power, http://ieer.org/wp/wp-content/uploads/2012/04/thorium2009factsheet.pdf By Arjun Makhijani and Michele Boyd A Fact Sheet Produced by the Institute for Energy and Environmental Research and Physicians for Social Responsibility
Thorium “fuel” has been proposed as an alternative to uranium fuel in nuclear reactors. There are not “thorium reactors,” but rather proposals to use thorium as a “fuel” in different types of reactors, including existing light-water reactors and various fast breeder
Thorium, which refers to thorium-232, is a radioactive metal that is
about three times more abundant than uranium in the natural
environment. Large known deposits are in Australia, India, and Norway.
Some of the largest reserves are found in Idaho in the U.S. The
primary U.S. company advocating for thorium fuel is Thorium Power
(www.thoriumpower.com). Contrary to the claims made or implied by
thorium proponents, however, thorium doesn’t solve the proliferation,
waste, safety, or cost problems of nuclear power, and it still faces
major technical hurdles for commercialization.
Not a Proliferation Solution
Thorium is not actually a “fuel” because it is not fissile and
therefore cannot be used to start or sustain a nuclear chain reaction.
A fissile material, such as uranium-235 (U-235) or plutonium-239
(which is made in reactors from uranium-238), is required to
kick-start the reaction. The enriched uranium fuel or plutonium fuel
also maintains the chain reaction until enough of the thorium target
material has been converted into fissile uranium-233 (U-
233) to take over much or most of the job. An advantage of thorium is
that it absorbs slow neutrons relatively efficiently (compared to
uranium-238) to produce fissile uranium-233.
The use of enriched uranium or plutonium in thorium fuel has
proliferation implications. Although U-235 is found in nature, it is
only 0.7 percent of natural uranium, so the proportion of U-235 must
be industrially increased to make “enriched uranium” for use in
reactors. Highly enriched uranium and separated plutonium are nuclear
In addition, U-233 is as effective as plutonium-239 for making nuclear
bombs. In most proposed thorium fuel cycles, reprocessing is required
to separate out the U-233 for use in fresh fuel. This means that, like
uranium fuel with reprocessing, bomb-making material is separated out,
making it vulnerable to theft or diversion. Some proposed thorium fuel
cycles even require 20% enriched uranium in order to get the chain
reaction started in
existing reactors using thorium fuel. It takes 90% enrichment to make
weapons-usable uranium, but very little additional work is needed to
move from 20% enrichment to 90% enrichment. Most of the separative
work is needed to go from natural uranium, which has 0.7% uranium-235,
to 20% U-235.
It has been claimed that thorium fuel cycles with reprocessing would
be much less of a proliferation risk because the thorium can be mixed
with uranium-238. In this case, fissile uranium-233 is also mixed with
non-fissile uranium-238. The claim is that if the uranium-238 content
is high enough, the mixture cannot be used to make bombs without a
complex uranium enrichment plant. This is misleading. More uranium-238
does dilute the uranium-233, but it also results in the production of
more plutonium-239 as the reactor operates. So the proliferation
problem remains – either bomb-usable uranium-233 or bomb-useable
plutonium is created and can be separated out by reprocessing.
Further, while an enrichment plant is needed to separate U-233 from
U-238, it would take less separative work to do so than enriching
natural uranium. This is because U-233 is five atomic weight units
lighter than U-238, compared to only three for U-235. It is true that
such enrichment would not be a straightforward matter because the
U-233 is contaminated with U-232, which is highly radioactive and has
very radioactive radionuclides in its decay chain. The
radiation-dose-related problems associated with separating U-233 from
U-238 and then handling the U-233 would be considerable and more
complex than enriching natural uranium for the purpose of bomb making.
But in principle, the separation can be done, especially if worker
safety is not a primary concern; the resulting U-233 can be used to
make bombs. There is just no way to avoid proliferation problems
associated with thorium fuel cycles that involve reprocessing. Thorium
fuel cycles without reprocessing would offer the same temptation to
reprocess as today’s once-through uranium fuel cycles.
Not a Waste Solution
Proponents claim that thorium fuel significantly reduces the volume,
weight, and long-term radiotoxicity of spent fuel. Using thorium in a
nuclear reactor creates radioactive waste that proponents claim would
only have to be isolated from the environment for 500 years, as
opposed to the irradiated uranium-only fuel that remains dangerous for
hundreds of thousands of years. This claim is wrong. The fission of
thorium creates long-lived fission products like technetium-99
(half-life over 200,000 years). While the mix of fission products is
somewhat different than with uranium fuel, the same range of fission
products is created. With or without reprocessing, these fission
products have to be disposed of in a geologic repository.
If the spent fuel is not reprocessed, thorium-232 is very-long lived
(half-life:14 billion years) and its decay products will build up over
time in the spent fuel. This will make the spent fuel quite
radiotoxic, in addition to all the fission products in it. It should
also be noted that inhalation of a unit of radioactivity of
thorium-232 or thorium-228 (which is also present as a decay product
of thorium-232) produces a far higher dose, especially to certain
organs, than the inhalation of uranium containing the same amount of
radioactivity. For instance, the bone surface dose from breathing an
amount (mass) of insoluble thorium is about 200 times that of
breathing the same mass of uranium.
Finally, the use of thorium also creates waste at the front end of the
fuel cycle. The radioactivity associated with these is expected to be
considerably less than that associated with a comparable amount of
uranium milling. However, mine wastes will pose long-term hazards, as
in the case of uranium mining. There are also often hazardous
non-radioactive metals in both thorium and uranium mill tailings.
Ongoing Technical Problems
Research and development of thorium fuel has been undertaken in
Germany, India, Japan, Russia, the UK, and the U.S. for more than half
a century. Besides remote fuel fabrication and issues at the front end
of the fuel cycle, thorium-U-233 breeder reactors produce fuel
(“breed”) much more slowly than uranium-plutonium-239 breeders. This
leads to technical complications. India is sometimes cited as the
country that has successfully developed thorium fuel. In fact, India
has been trying to develop a thorium breeder fuel cycle for decades
but has not yet done so commercially.
One reason reprocessing thorium fuel cycles haven’t been successful is that uranium-232 (U-232) is created along with uranium-233. U-232, which has a half-life of about 70 years, is extremely radioactive and is therefore very dangerous in small quantities: a single small
particle in a lung would exceed legal radiation standards for the
general public. U-232 also has highly radioactive decay products.
Therefore, fabricating fuel with U-233 is very
expensive and difficult.
Not an Economic Solution
Thorium may be abundant and possess certain technical advantages, but
it does not mean that it is economical. Compared to uranium, the
thorium fuel cycle is likely to be even more costly. In a once-through
mode, it will need both uranium enrichment (or plutonium separation)
and thorium target rod production. In a breeder configuration, it will
need reprocessing, which is costly. In addition, as noted, inhalation
of thorium-232 produces a higher dose than the same amount of
uranium-238 (either by radioactivity or by weight).
Reprocessed thorium creates even more risks due to the highly
radioactive U-232 created in the reactor. This makes worker protection
more difficult and expensive for a given level of annual dose. Fact
sheet completed in January 2009
Updated July 2009
Clean Technica (http://s.tt/1n2ee)
Why Thorium Nuclear Isn’t Featured on CleanTechnica
Clean Technica, SEPTEMBER 11, 2012 BY ZACHARY SHAHAN
Update: I have published a new post on this matter (thorium) that
includes two rebuttals to the below reposted paper.
Now, before I get into the details of why thorium is anything but
awesome, I want to say a few things about the culture that surrounds
the “thorium will solve all our problems!” idea. Thorium enthusiasts
are often willing to make claims like, “if it weren’t for the
government, we would have switched to thorium nuclear energy decades
ago.” Or, “thorium nuclear will solve all our problems, but it’s been
suppressed by big government for decades.”
Clean Technica (http://s.tt/1n2ee)……...
there are legitimate reasons why wind and solar energy are blowing up
in use and popularity but thorium is not. There’s a good reason (or
many good reasons) why wind turbines and solar panels are in place all
over the world, but there isn’t a single commercial thorium reactor in
operation. It’s not because every government in the world is
suppressing thorium. It’s most likely because thorium simply isn’t
what its proponents say it is.
Clean Technica (http://s.tt/1n2ee)