(John Kemp is a Reuters market analyst. The views expressed are
By John Kemp
LONDON, March 24 Japan will transfer all the
highly enriched uranium and separated plutonium held at the
country's fast critical assembly facility to the United States,
the two countries said in a joint statement on Monday.
"This effort involves the elimination of hundreds of
kilograms of nuclear material, furthering our mutual goal of
minimizing stocks of highly enriched uranium and separated
plutonium worldwide, which will help prevent unauthorized
actors, criminals, or terrorists from acquiring such materials,"
according to the White House.
"This material, once securely transported to the United
States, will be sent to a secure facility and fully converted
into less sensitive forms."
The announcement was timed to coincide with the Nuclear
Security Summit in the Netherlands, attended by more than 50
world leaders, including U.S. President Barack Obama and Chinese
President Xi Jinping.
The transfer is mostly symbolic but it comes after China
complained last month Japan is stockpiling nuclear materials
that could be used in a future bomb-making programme ("Japan to
let U.S. assume control of nuclear cache" New York Times, March
It underscores U.S. determination to resist the spread of
dangerous technologies as much as possible and reinforce the
The United States continues to press countries with civilian
reactors to forego enrichment and reprocessing, and instead rely
on international processing facilities operated by existing
nuclear weapons states and other reliable suppliers in Europe.
The proliferation risks posed by nuclear programmes in Iran,
North Korea, Israel, Pakistan and India are well known. But
dozens of other countries are also accumulating enormous
quantities of fissile materials as part of civilian energy
Experts fear these stocks could be used to assemble a
nuclear bomb quickly, if a government decided it needed a
nuclear deterrent, or stolen by terrorists to produce a
radiological weapon (a so-called "dirty bomb").
"As of January 2013, the global stockpile of highly enriched
uranium is estimated to be about 1,390 tonnes," according to the
International Panel on Fissile Materials, an independent group
of arms control and non-proliferation experts from both nuclear
weapon and non-nuclear weapon states founded in 2006.
"The global stockpile of separated plutonium is about 490
tonnes, of which about 260 tonnes is the material in civilian
custody," the panel estimates (fissilematerials.org).
Proliferation experts are concerned about poor security
around some civilian stockpiles, as well as the practice of
shipping large quantities of spent nuclear fuel and plutonium
between producing states and countries with reprocessing
There is no evidence any of this material has been diverted
for military purposes. But just a few kilograms of plutonium or
highly enriched uranium is all that is needed to make an atomic
weapon, and even less is needed for a dirty bomb, so civilian
stockpiles could potentially be used to make thousands of
Less than 1 percent of the uranium ore occurring naturally
is the fissile isotope uranium-235 (U-235). The rest is the more
stable isotope uranium-238 (U-238) which is no use for power
production or bomb-making.
Some reactor designs use uranium in its natural state, but
most need the proportion of U-235 to be raised in order to work
effectively. Before being manufactured into reactor fuel,
natural uranium is therefore enriched by gaseous diffusion or
ultra-fast centrifuges arranged in cascades.
Both methods exploit the small mass difference to separate
some of the lighter U-235 from the heavier U-238. By repeating
the process enough times, the concentration of U-235 can be
raised to any desired level.
For civilian power reactors, the U-235 content is typically
raised to between 3 percent and 5 percent (low enriched uranium,
But some research reactors and those producing medical
isotopes require the proportion of U-235 to be increased to 20
percent or more (highly enriched uranium, HEU). Uranium for
nuclear weapons is enriched to 90 percent.
The enrichment process is essentially the same whether LEU
is being produced for civilian power reactors or weapons-grade
uranium is being produced for bombs.
"The development of atomic energy for peaceful purposes and
the development of atomic energy for bombs are in much of their
course interchangeable and interdependent," according to a U.S.
government report in 1946.
Because of the large volume of material that must be handled
in the early stages, enriching uranium from 1 percent to 2
percent requires lots of centrifuges. But as the proportion of
U-235 rises, the volume of material that has to be handled
declines, and further enrichment becomes simpler.
"By producing LEU of 3-5 percent enrichment, much of the
separative work (approximately 70-88 percent) necessary for
getting to weapons grade is already done," according to experts
from Los Alamos National Laboratory and Stanford University's
Center for International Security and Cooperation.
"Only a fraction of the cascades used for a full-scale
commercial enrichment facility would need to be diverted or
constructed to produce sufficient weapons-grade HEU for a few
bombs per year," they explain ("Nuclear non-proliferation" in
"Fundamentals of materials for energy and environmental
According to the International Panel on Fissile Materials,
12 countries are known to operate enrichment facilities: Russia,
the United States, France, the United Kingdom, Germany, the
Netherlands, Japan, Argentina, Brazil, India, Pakistan and Iran.
North Korea is also believed to have an operational enrichment
Counter-proliferation experts, especially from the United
States, have sought to discourage countries from enriching their
own uranium. But many countries with civilian power programmes,
including Iran, claim enrichment is one of their rights under
the Non-Proliferation Treaty (NPT) and want to enrich their own
fuel for security reasons.
Once uranium has been enriched, it is usually manufactured
into cylindrical pellets 5-12 millimetres in diameter. The
pellets are then inserted into zirconium-alloy tubes about 1-4
metres long known as fuel rods or pins. Multiple fuel rods are
bundled together in a fuel assembly that is inserted into the
In a typical once-through or open fuel cycle reactor, the
fuel is used just once. But when the spent fuel is removed from
the reactor, only around 5 percent of the fissile material has
been used up.
It is more efficient to run the reactor this way, in terms
of optimising its performance, but means 95 percent of the
fissile material inside the fuel rods goes unused, which is
It also generates enormous volumes of highly radioactive
waste that must be stored safely. Spent fuel assemblies are
generally stored in giant cooling ponds as the remaining fissile
material continues to decay and give off enormous amounts of
heat that must be removed to prevent damage to the fuel
To resolve some of these problems, France, Japan and Russia
have developed closed fuel cycles in which spent fuel is sent to
be reprocessed. Unused fissile materials are reclaimed,
fashioned into new fuel rods, and run through the reactor again.
The problem is that the radioactive decay of uranium results
in a host of different products, many of which are themselves
radioactive. Some isotopes are short-lived, like strontium-92
and iodine-128, but others like plutonium-239 are much
longer-lasting and ideal for making atomic weapons ("The nuclear
fuel cycle: from ore to waste" British Nuclear Fuels, 1996).
Reprocessing operations separate these different materials
and return them to the client, including the highly toxic and
The first reprocessing facilities were built to separate
plutonium for weapons. But today Britain, France and Russia all
reprocess reactor fuel for civilian purposes, including fuel
However, the United States decided in 1977 it would defer
reprocessing indefinitely. President Jimmy Carter stated a
moratorium was necessary to reduce the serious threat of
proliferation and set an example for other countries. As a
result, all U.S. spent fuel remains in storage at each plant
where it was used.
Reprocessing makes much more efficient use of the world's
finite stocks of usable uranium. If a large proportion of global
electricity demand is to be met from nuclear reactors in future
to help avert global warming, reprocessing may be essential.
Separation of plutonium is, however, a major proliferation
risk. Ordinary reactor-grade plutonium is not ideal for making
weapons. But both India and the United States have successfully
detonated nuclear devices made from reactor-grade plutonium
reclaimed from civilian reactors.
(Editing by William Hardy)