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Thinking the Unthinkable: Japanese nuclear power and proliferation in East Asia

September 28, 2005
Volume 3 | Issue 9
Article ID 1931

Thinking the Unthinkable: Japanese nuclear power and proliferation in East Asia

By Frank Barnabie and Shaun Burnie

As we reach the anniversary of the end of World
War II, North-east Asia has changed in so many
ways since the devastation brought about by years
of conflict. But tragically, many historical problems
remain unresolved. The Korean peninsula is still
divided; the United States is the predominant
military power in the region; and nationalism
remains a powerful force in Japan, China and in the
Koreas. These alone should give rise to major
concern for the future peace and stability of the
region. But the threats to peace in the region could
soon get worse.

Sixty years ago the city of Nagasaki was destroyed
by one nuclear bomb containing five kilograms of
plutonium. In 2005, Japan has one of the largest
stocks of weapons usable plutonium in the world
(45,000 kg and growing) as well as access to the
most advanced missile technology. This is not by
accident but design. Deliberate policy established
in the late 1960’s by senior politicians was to
acquire the nuclear material required for atomic
bombs, and the means to deliver them.1 Without
having to cross the difficult threshold of actual
weapons development, Japan has already become a
de facto nuclear weapons state.

Successive Japanese governments have achieved
this status through a nuclear energy policy based
upon the production and use of plutonium, and an
ambitious if flawed commercial space programme.
It is this nuclear policy that will soon lead to the
commissioning of the world’s most expensive
nuclear facility - the Rokkasho-mura reprocessing

The big question is whether or not a future
Japanese government will take a political decision
to develop nuclear weapons. Nuclear proliferation
threats on the Korean peninsula and the growth of
China’s economic and military power are two
important (and real) drivers that are being cited by
powerful interests in Japan as justification for
considering what should be the unthinkable.
So at a time when the tensions, and therefore the
proliferation dynamics in North-east Asia, are
becoming both more serious and complex, there is
an urgent need to examine both Japan’s plutonium
programme and the political context of Japan’s
nuclear weapons policy. This briefing will seek to
focus on a few of these.


Unlike South Korea and Taiwan, which had their
pursuit of reprocessing and plutonium frustrated
by direct U.S intervention, Japanese nuclear
energy policy since the 1960’s has been based
upon the large-scale production and use of
plutonium. The original plan to separate plutonium
from nuclear reactor spent fuel and then use it to
fuel a generation of fast breeder reactors has
failed, with only the Monju fast reactor remaining.
Instead the plan to use plutonium as fuel is
dependent upon successful loading in conventional
light water reactors. This plan too has run into
major delays due to the reality of unsafe technology,
poor operating standards, and a determined antinuclear
movement that has, over recent decades,
challenged all major developments.

Whereas in 1994, Japanese officials were
predicting that plutonium demand (the amount
required to fuel nuclear power plants) would be
85-90,000 kg by 2010, today in 2005 not one
gram of plutonium is loaded into commercial
nuclear power reactors. Moreover, while the
demand side has been a disaster for Japanese
government plans, its plutonium supply has run
out of control, with total plutonium stocks over 45
metric tons - a fivefold rise from the early 1990’s.
This could rise to over 100 tons within the next
fifteen years.

To date most of this plutonium has accumulated in
overseas reprocessing plants in France and the UK
under contracts signed with Japan. However, with
plans to start up the US$21 billion Rokkasho
plant, Japan will have a reprocessing capacity only
equalled by the world’s largest nuclear weapons

The pursuit of plutonium

“Can Japan expect that if it embarks on a
massive plutonium recycling program that
Korea and other nations would not press
ahead with reprocessing programs? Would
not the perception of Japan’s being awash
in plutonium and possessing leading edge
rocket technology create anxiety in the
Diplomatic cable U.S. Ambassador to Japan,
to U.S. Secretary of State Christopher,
March 1993.

Japan’s no-plutonium stockpile policy

In response to political pressure over its plutonium
programme, the Japanese government declared in
the early 1990’s that it would not hold more
plutonium than was necessary for commercial use.
The government’s ‘no plutonium stockpile’ policy
and their declared supply and demand figures for
plutonium, were meant to reassure the international
community, particularly in East Asia, that Japan
would only possess sufficient plutonium to meet
commercial requirements. However, almost from
day one, Japan has possessed well in excess of its
requirements, and as the 1990’s unfolded the excess
stock has increased.

“The squishy part of the Japanese plan,
where the numbers appear vague and
uncertain, is the use of MOX fuels in
commercial reactors. If use is less than
planned Japan will have to slow down its
reprocessing and accumulate growing
amounts of unreprocessed spent fuel, or will
have to produce separated plutonium that is
clearly excess to Japan’s civilian needs.”
U.S. Embassy diplomatic cable to U.S. Secretary
of State, ‘Japanese plutonium transport and
reprocessing issues’, November 15th 1991.

Nearly fifteen years on and the only thing that has
changed is the volume of Japanese plutonium.
Japanese plans for plutonium fuel (MOX) use
remain highly ‘squishy’ or uncertain. At the time of
this diplomatic cable (1991) Japan had a total of
9,000 kg of plutonium. The current stockpile has
increased fivefold to nearly 45,000 kg.

In 1991, Japan’s Atomic Energy Commission
predicted that by 2010:
• 50 tons of plutonium in MOX would be
loaded into light water reactors
• 10 tons of plutonium in MOX loaded in
Advanced Thermal reactors;
• 20-30 tons of plutonium in MOX loaded
into Fast Breeder reactors.

In reality these projections have been completely
wrong. If we add Japan’s current available
plutonium stockpile (45,000 kg) to the cumulative
supply of plutonium from Rokkasho operations
through to 2020 (100,000 kg), by 2020 Japan’s
plutonium stockpile will reach 145 metric tons. It
is clear that Japan has become the world’s largest
holder of weapons-usable plutonium, far
surpassing that contained in the United States
nuclear weapons arsenal of 100 tons.

“I admit that we have excessive amounts of
plutonium, but our purpose is for
Yuichi Tonozuka, president of the Japan Nuclear
Cycle Development Institute, April 2005.

No such justification would be permissible by a
South Korean nuclear official, because the United
States blocks Seoul from acquiring plutonium.
Still, it is almost inconceivable that Japan’s plans
for plutonium MOX fuel by 2020 will use more
than forty or so tons of plutonium. The history of
Japan’s programme would suggest that they will
fail to utilize even this amount. Thus Japan’s
stockpile of plutonium will continue to grow with
all the resultant negative consequences for global
nuclear non-proliferation and regional peace and

The 2005 Non-Proliferation Treaty (NPT) conference
failed to reach any sort of consensus. It is, therefore,
urgent to strengthen the NPT regime and revitalise the
Treaty. In the short term, the most important
measure to do so is to strengthen the safeguards
system applied by the International Atomic Energy
Agency (IAEA), to make it more difficult to acquire
fissile materials, plutonium and highly enriched
uranium, to make nuclear weapons.

The most serious problem facing the IAEA
safeguards system is that the most sensitive plants
insofar as the diversion of weapon-usable materials
is concerned - particularly uranium-enrichment
facilities and plutonium reprocessing plants - are
impossible to safeguard effectively.3 Consider, for
example, large commercial reprocessing plants
which separate the unused uranium, plutonium and
fission products in spent nuclear power reactor fuel
elements, such as the one under construction at

Safeguarding the plutonium in spent nuclear reactor
fuel elements before reprocessing is relatively
simple. It is just a matter of counting the number of
the elements. Once the plutonium is removed from
spent reactor fuel elements at Rokkasho-Mura,
safeguarding it is quite a different matter. There is
no clear distinction between the commercial use of
plutonium and its military use. To argue that the
further spread of nuclear weapons must be
prevented, as Japan does, while, at the same time,
operating a civil reprocessing plant is, to say the
least, inconsistent.

A good nuclear-weapons designer could construct a
nuclear weapon from three or four kilograms of the
plutonium produced by the Rokkasho-Mura
reprocessing plant. To ensure the timely detection
of the diversion of such a small amount of
plutonium in a plant where so much plutonium is
handled requires very precise safeguard
techniques, requiring significantly more precision
than is currently achievable. Even with the best
available and foreseeable safeguards technology it
is not possible to get the precision necessary.4

The Rokkasho-Mura Reprocessing Plant cannot be
safeguarded and should be abandoned

In August 2004, a leak started in a pipe connected
to the accountancy tank at the front end of the
THORP reprocessing plant at Sellafield and
complete failure of the pipe occurred in mid-
January 2005.5 Solution, containing spent reactor
fuel elements dissolved in nitric acid, leaked into a
cement secondary containment chamber. The leak
was not detected until April 2005, eight months
after it began, by which time about 83,000 litres,
containing about 160 kg of plutonium, had leaked
out. Opportunities to detect the leak - cell
sampling and level measurements - were missed.
That this incident could have occurred is one
example of the inadequacies of the safeguards
system for reprocessing plants.

The main reason for the difficulty of safeguarding
the Rokkasho-Mura plant relates to uncertainty
about the amount of plutonium entering the plant.
An estimate of this amount is made from the
amount of uranium in the spent reactor fuel
elements sent to the reprocessing plant by the
Japanese operators of the reactors. This is
calculated by the reactor operators from their
knowledge of the amount of uranium originally in
the reactor fuel elements and of the way in which
the reactor was operated while the fuel was in it. In
particular the amount of heat produced by the fuel.
The estimate relies on computer calculations not
direct measurement.

The first measurement, as opposed to an estimate
based on calculation, of plutonium in the
Rokkasho-Mura reprocessing plant is made on
samples taken from an accountancy tank at the
beginning of the process. Using mass spectrometry,
the ratio of the amount of plutonium to the amount
of uranium is determined. From the calculated
amount of uranium and the measured
uranium/plutonium ratio, the amount of plutonium
is calculated.6

There may be errors in each stage of this operation.
For example, some plutonium will remain in the
parts of the fuel elements not dissolved in the nitric
acid (called “the hulls”). The amount is very
difficult to estimate.

The operators of the Rokkasho-Mura reprocessing
plant will, therefore, be uncertain about the precise
amount of plutonium produced by the plant. The
uncertainty is called the “material unaccounted for”
or MUF. Because of the nature of the errors
involved, the value of the MUF will usually not be
zero even if no illegal diversion of plutonium has

The fact that there is a MUF means that the
operators of a commercial reprocessing plant do
not know whether or not an amount of plutonium
has gone missing. For example, if the police ring
up the operators and say that a terrorist or criminal
group has contacted them and provided evidence
that they have acquired some plutonium, enough to
fabricate a nuclear explosive, the operators could
not confirm with any certainty that a few kilograms
had, or had not, gone missing. This is because the
amount that may be missing will be within the
MUF. It must be concluded that currently the IAEA
cannot effectively safeguard the Rokkasho-Mura
reprocessing plant.

According to recent estimates, the potential
material unaccounted for (MUF) at the Rokkasho-
Mura plant will be around 50 kg per year. This
plant, which will include the most up-to-date
safeguards technologically available, is designed to
allow the application of the most effective
safeguards possible today. The plant will have the
capacity to reprocess about 800 tonnes of spent fuel
a year, producing about eight tonnes of plutonium.
The effectiveness of safeguards on the plant,
according to these estimates, is more than 99%.
Nevertheless, even on these very optimistic
estimates, the potential material unaccounted for
still amounts to about a nuclear weapon’s worth a

We realise that the official response to MUF is to
claim that even if plutonium goes astray from the
reprocessing plant, physical protection measures
applied will prevent it leaving the site. We disagree
with this and question the effectiveness of physical
protection, and therefore still believe the safeguard
system is inadequate.

The Japanese nuclear industry is keen to reprocess
spent reactor fuel because it recovers unused
uranium and plutonium that can be reused as
nuclear fuel. The fact that there may be some
plutonium unaccounted for at Rokkasho-Mura is
acknowledged, but it is argued that physical
protection measures can be made sufficiently
effective at the plant to ensure that no significant
amounts of plutonium are removed from the site.
Those anxious to prevent the use of plutonium for
the production of nuclear weapons by the
government or by terrorists argue that any
significant amount of plutonium unaccounted for is
unacceptable and that reprocessing at Rokkasho-
Mura plant should be abandoned.

There is no need to reprocess spent nuclear power
reactor fuel elements. Civil spent reactor fuel
elements can stored until they can be permanently
disposed of in a geological repository - such as the
one planned by the USA at Yucca Mountain.
Plutonium is generally used as nuclear-reactor fuel
in the form of mixed oxide (MOX) fuel. The plan
is to produce MOX at the Rokkasho-Mura plant by
mixing uranium dioxide and plutonium dioxide.
This can be used as fuel in Japanese nuclear-power
reactors instead of uranium dioxide.

MOX enthusiasts argue that the use of MOX
allows plutonium to generate more energy in
nuclear reactors rather than wasting this energy,
and that the use of MOX would reduce the
stockpiles of civil Japanese plutonium. These
stockpiles are politically embarrassing for the
Japanese government because the plutonium could
be used to fabricate nuclear weapons. The cost of
MOX fuel is, however, much higher than the cost
of ordinary uranium dioxide fuel.

The use of MOX increases the risk of nuclear weapon
proliferation. The necessary steps of
chemically separating the plutonium dioxide from
uranium dioxide and converting the dioxide into
plutonium metal that can be used to fabricate
nuclear weapons are relatively straightforward.
The use of MOX in a nuclear-power reactor is not
a satisfactory solution to the problem of excess
plutonium stocks. A more rational solution would
be to abandon reprocessing at Rokkasho-Mura and
to immobilize existing stocks of Japanese
plutonium until they can be permanently disposed

Safeguards and, therefore, the non-proliferation
regime, would be significantly strengthened if
reprocessing and the production and use of MOX
at the Rokkasho-Mura plant were abandoned. This
would significantly improve global security.
Not one country that has initiated a nuclear
weapons programme since 1945 has done so on
the basis of a democratic debate.7 Decisions were
made behind closed doors in great secrecy and in
the context of external threats - actual, perceived,
contrived and otherwise. In the case of Japan
there is a dangerous assumption that the decision
to build nuclear weapons will require the
overturning of public opinion, which is generally
considered to be by majority opposed to nuclear
weapons. History informs us that conditions
evolve that lead to debate and opposition after the
threshold has been crossed, by which time it is too

Today, Japan is closer to those conditions than at
any time since at least the 1960’s, and probably
since its wartime programme in the 1940’s. In the
case of the military programs run by the Imperial
Navy and Army under the guidance of the father
of the Japanese atom, Nishina Yoshio, it was lack
of time, resources and fissile material that led to
failure.8 In the 1960’s it was the political
judgement that it was not in Japan’s national
interest to acquire the bomb - it could rely upon
the U.S. nuclear guarantee (at least for the
foreseeable future) and at the same time acquire
the means to go nuclear if necessary.

With the technical means to build advanced
nuclear weapons within six months, what remains
is the political judgement of the ruling elite of
Japan first to assess its strategic imperatives and
then the political consequences of going nuclear.
As a de-facto nuclear weapons state under the
U.S. nuclear umbrella, there remains today no
immediate need for Japan to build nuclear
weapons. Its plutonium stockpile is already a
strategic asset. But the conditions for a decision
are evolving, and the public is being softened up
for a possible decision.

Since the 1950’s leading politicians, including
Prime Ministers and Cabinet Secretaries have
pronounced on the possibility of Japan developing
nuclear weapons. Many of these statements have
made clear that the Japanese constitution does not
prohibit Japan possessing nuclear weapons and
that its three non-nuclear principles are not legally

Political momentum towards nuclear weapons

Through most of this period the justification has
been for obvious reasons, put in the context of
national (self) defence, but in most cases without
explicit threats being named (at least in public).
Today the threats are now more explicitly cited. In
recent years leading politicians such as
Ozawa Ichiro warned that Japan could use its commercial
plutonium stockpile for making nuclear weapons.
Ozawa, leader of the opposition party Jiyuto
(Liberal Party), declared in 2002 that if the military
threat posed by China continued to grow:
“It would be so easy for us to produce
nuclear warheads - we have plutonium at
nuclear power plants in Japan, enough to
make several thousand such warheads.”9

The crisis over North Korea’s nuclear weapons
program, based around plutonium reprocessing,
stengthened the position of those in Japan
advocating nuclear weapons development.

Acknowledged by no less than the U.S.
Ambassador to Japan Thomas Schieffer: “If you
had a nuclear North Korea, it just introduces a
whole different dynamic… That increases the
pressure on both South Korea and Japan to
consider going nuclear themselves.” (Tokyo, June
2005). While such a declaration is intended to put
pressure on China to act more forcefully with its
ally in Pyongyang, it is also highly significant in
terms of U.S. policy towards Japan.

In the 1960’s, the Nixon administration considered
the option of arming Japan with nuclear weapons.
Forty years on it would be surprising if there were
not those in Washington considering that such a
development would be in the medium term
interests of the United States. And anyway, the
U.S. is already signalling that it would not be able
to stop it.

Of course, according to most analysts North Korea
already possesses a few or several nuclear
weapons. It has not yet demonstrated their
existence through an actual nuclear test, although it
has been speculated that it is imminent. At which
point the debate in Japan over its security
vulnerability to North Korean missiles would
become frantic.

More likely a test remains a threat, which will be
deployed only when North Korea has run out of
other options. But the general atmosphere remains
threatening and therefore fertile for those in Japan
who would move towards weaponisation.

A further factor to consider is the general view that
international opprobrium/condemnation would be
visited on Japan if it were to go nuclear. It is true
that the consequences for Japan’s nuclear trade
would be problematic, perhaps severely damaging
as Japan is supplied nuclear materials and
technology under condition of peaceful use. But
what of wider diplomatic and economic

It is worth considering the reality of international
relations in the early 21st century. Japan’s major
nuclear trading partners are in possession of their
own nuclear weapons (and currently modernizing
them) or covered by the U.S. nuclear umbrella.
Current nuclear non-proliferation policy is based
upon the double-standards of opposing the
programmes of Iran or North Korea while
maintaining or expanding their own weapons
programs. Japan is unlikely to be labelled part of
the axis of evil. If triggered by a North Korean test,
or equivalent dramatic development, while not
welcoming a Japanese bomb, it is likely that
Japan’s allies would explain it as a regrettable but
understandable reaction.

And it gets worse. Witness the experience of India
and Pakistan in the aftermath of their nuclear
weapons tests in 1998. While sanctions were
applied, including by Japan, the reality today is
that their relations with the United States and allies
(especially Japan) have never been closer. They are
both identified as strategic partners, with India seen
as vital in terms of economic production and future
markets, an ally in the ‘war against terror’ in the
case of the military elite ruling Pakistan, and a
counter balance to China in the case of India. The
reality is that both countries have gotten away, nay
thrived, in the aftermath of becoming nuclear
powers. India is due to sign nuclear cooperation
agreements with the United States and Pakistan is
soon to take delivery from the U.S. of nuclear
strike capable F-16s.

As the world’s second largest economy, the
important and dangerous lesson for policy makers
in Japan is that the world soon learns to live with
nuclear realities. If India and Pakistan can do it,
then Japan certainly can. Japan’s strategic
importance to the United States has moved centre
stage under the Bush administration. There are
pressures to revise its constitution with the active
encouragement of the U.S., and Japan’s military is
being deployed overseas, and undertaking joint
training with the U.S. as never before. The
prospects of Japan moving further towards
nationalism and militarism are made worse by the
likely successor to Prime Minister Koizumi, Shinzo
Abe in 2006.

“Treat nothing as inevitable” is a good principle to
live one’s life by. Unfortunately, in the case of
Japan’s nuclear development, it may not be
sufficient. The international community - read
governments - will learn to live with Japanese
nuclear weapons if that occasion arises. The
consequences would of course be terrible for Northeast
Asia. Pressure in South Korea to respond
would be huge, relations with China could become
disastrous, and the global nuclear non-proliferation
regime centred around the NPT reduced to a
historical footnote.

Japan’s existing plutonium programme is a driver
for nuclear proliferation in the East Asian region
and further afield. For example, Iran has cited
Rokkasho to support its case for being permitted to
complete its uranium enrichment plant at Natanz.
There is an alternative to Japan travelling full circle
from the ashes of 1945 and becoming a declared
nuclear weapon state. It will come through active
citizen opposition in Japan based upon informed
debate and mobilization, aided by support from
overseas. A change in energy policy that abandons
plutonium use on the grounds of non-proliferation
would be an important first towards rejecting the
path chosen by governments (but not the people) in
the world’s nuclear weapons states. It will also
strengthen Japan’s calls for global nuclear

The nuclear weapon states, in particular the United
States, continue to defy their legal obligations to
disarm their nuclear weapons. The 60th anniversary
of the first use of the atomic bomb is a hugely
important opportunity to begin the mobilization not
just in Japan

1. Mainichi Shimbun, in its 1st August 1994 edition,
revealed that a top secret Foreign Ministry document
called “Our Nation’s Foreign Policy Principles” was
produced in 1969.
2. Total costs for the plant are US$21 billion. See,
“Nuclear Twilight Zone”, Bulletin of Atomic Scientists.
May 2001.
3. Leventhal, P., “IAEA Safeguards Shortcomings: A
Critique”, Nuclear Control Institute, Washington, DC.,
September 12th, 1994
4. Miller, M. M., “Are IAEA Safeguards on Plutonium
Bulk-Handling Facilities Effective?”, Nuclear Control
Institute, Washington, DC., August 1990.
5. Nuclear Engineering International, Thorp board of
enquiry report released, Nuclear Engineering
International, 29th June 2005.
6. Frank Barnaby and Shaun Burnie, “Safeguards on the
Rokkasho reprocessing plant”, Greenpeace
International, June 2002.
7. The U.S. Manhattan project for obvious reasons was
launched without Congressional debate; both France
and the UK launched theirs with limited cabinet
involvement and no parliamentary debate; the Soviet
and Chinese program were initiated under direct orders
of Stalin and Mao; India announced their program with
a nuclear test in 1974; Pakistan similarly in 1998; Israel
still refuses to officially confirm its program exists;
South Africa dismantled its weapons only after the end
of Apartheid and democratic elections. Programs run by
Australia, Switzerland, Germany, Sweden, South Korea
and Taiwan to name the most sophisticated were done
so in great secrecy, with limited parliamentary debate in
a few cases.
8. The first English language report confirming Japan’s
nuclear weapons program was made by David Snell in
the October 3rd edition of the Atlanta Constitution, the
headline read, “Japan Developed Atomic Bomb -
Russians Grabbed Scientists”. More substantive details
on Japan’s wartime bomb program, Genzai Bakudan,
were provided by Deborah Shapely in Science, vol. 199,
Jan. 13th, 1978. While Snell claimed that Japan
progressed to the point where it conducted a nuclear test
on August 10th 1945, off the coast of present day North
Korea, there remain significant doubts that such a test
took place. The latest thinking is that without sufficient
fissile material Japan was 6-9 months away from an
actual weapon.
9. Ozawa’s statement was made during a lecture given
in the southern City of Fukuoka, though was not
supposed to be made public, April 2002, see
Greenpeace International press statement, “Ozawa
confirms nuclear weapons potential of Japan’s
plutonium program as further nuclear transports loom”,
April 7th 2002.

This is an abbreviated version of a report published by the Oxford Research Group and Citizens’ Nuclear Information Center of Tokyo
For the full report see The Nautilus Institute website

Dr. Frank Barnaby is a Nuclear Issues Consultant to Oxford Research Group (ORG), and has been on ORG’s Council of Advisers since its inception. He is a nuclear physicist by training. He was Executive Secretary of the Pugwash Conferences on Science and World Affairs in the late 1960s and Director of the Stockholm International Peace Research Institute from 1971-81. He is now a freelance defence analyst, and is a prolific author on military technology. His most recent book is How to Build a Nuclear Bomb (Granta, 2003).

Shaun Burnie is Coordinator of Greenpeace International nuclear campaigns. Based in Scotland, he has worked in Japan and Korea since 1991. He writes in a personal capacity and this briefing does not necessarily reflect the views of Greenpeace International. Further background on issues raised in this briefing include: Planning for Failure: Nuclear Safeguards at the Rokkasho-mura plant, Burnie/Barnaby, Greenpeace International, 2002; and most recently a report on advanced nuclear technology developments in North-east Asia at the International Conference on Proliferation Challenges in North-east Asia: The Korean Peninsula and Japan, April 2005, National Assembly Seoul. Reports available from

Posted at Japan Focus September 8, 2005.