Thorium Fuel: No Panacea for Nuclear Power
Edited on Thu Mar-11-10 12:34 AM by kristopher
(Open Access Document)
Thorium Fuel: No Panacea for Nuclear Power
By Arjun Makhijani and Michele Boyd
A Fact Sheet Produced by the Institute for Energy and Environmental Research and Physicians for Social Responsibility
“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 reactor designs.
Thorium, which refers to thorium‐232, is a radioactive metal that is about three times more
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
Not a Proliferation Solution
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.
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 weapons materials.
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.
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‐usable
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
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 the an amount (mass) of insoluble thorium is about 200
times that of breathing the same mass of uranium.
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
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. Besi
des 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
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
may be abundant and possess certain technical advantages, but it does
not mean that it is economical. Compared to uranium, 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, inhalati on 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. 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
Fact sheet completed in January 2009
Updated July 2009
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