Japan's Nuclear Future: Policy Debate, Prospects, and U.S. Interests

Japan’s Nuclear Future:
Policy Debate, Prospects, and U.S. Interests
May 9, 2008
Emma Chanlett-Avery
Analyst in Asian Affairs
Foreign Affairs, Defense, and Trade Division
Mary Beth Nikitin
Analyst in Nonproliferation
Foreign Affairs, Defense, and Trade Division

Japan’s Nuclear Future:
Policy Debate, Prospects, and U.S. Interests
Japan, traditionally one of the most prominent advocates of the international
non-proliferation regime, has consistently pledged to forswear nuclear weapons.
Nevertheless, evolving circumstances in Northeast Asia, particularly North Korea’s
nuclear test in October 2006 and China’s ongoing military modernization drive, have
raised new questions about Japan’s vulnerability to potential adversaries and,
therefore, the appeal of developing an independent nuclear deterrent. The previous
taboo within the Japanese political community of discussing a nuclear weapons
capability appears to have been broken, as several officials and opinion leaders have
urged an open debate on the topic. Despite these factors, a strong consensus — both
in Japan and among Japan watchers — remains that Japan will not pursue the nuclear
option in the short-to-medium term.
This paper examines the prospects for Japan pursuing a nuclear weapons
capability by assessing the existing technical infrastructure of its extensive civilian
nuclear energy program. It explores the range of challenges that Japan would have
to overcome to transform its current program into a military program. Presently,
Japan appears to lack several of the prerequisites for a full-scale nuclear weapons
deterrent: expertise on bomb design, reliable delivery vehicles, an intelligence
program to protect and conceal assets, and sites for nuclear testing. In addition, a
range of legal and political restraints on Japan’s development of nuclear weapons,
including averse public and elite opinion, restrictive domestic laws and practices, and
the negative diplomatic consequences of abandoning its traditional approach is
Any reconsideration and/or shift of Japan’s policy of nuclear abstention would
have significant implications for U.S. policy in East Asia. In this report, an
examination of the factors driving Japan’s decision-making — most prominently, the
strength of the U.S. security guarantee — analyzes how the nuclear debate in Japan
affects U.S. security interests in the region. Globally, Japan’s withdrawal from the
Nuclear Non-Proliferation Treaty (NPT) would damage the world’s most durable
international non-proliferation regime. Regionally, Japan “going nuclear” could set
off an arms race with China, South Korea, and Taiwan. India and/or Pakistan may
then feel compelled to further expand or modernize their own nuclear weapons
capabilities. Bilaterally, assuming that Japan made the decision without U.S.
support, the move could indicate a lack of trust in the U.S. commitment to defend
Japan. An erosion in the U.S.-Japan alliance could upset the geopolitical balance in
East Asia, a shift that could strengthen China’s position as an emerging hegemonic
power. All of these ramifications would likely be deeply destabilizing for the
security of the Asia Pacific region and beyond.
This report will be updated as circumstances warrant.

In troduction ......................................................1
Background ......................................................2
An Evolving Security Environment in Asia.............................3
Japan’s Nuclear Capacity............................................4
Japan’s Nuclear Energy Program..................................4
Technological Potential.........................................6
Japanese Legal and Political Restraints.................................7
Domestic Factors..............................................7
Public Opinion............................................7
Elite Opinions............................................8
Constitutional Restraints....................................8
1955 Atomic Energy Basic Law..............................8
Three Non-Nuclear Principles................................9
External Factors...............................................9
International Law..........................................9
Consequences for Civilian Nuclear Program.....................9
International Diplomatic Consequences.......................10
Issues for U.S. Policy..............................................10
U.S. Security Commitment.................................10
Potential for Asian Arms Race..............................12
U.S.-China Relations......................................12
Future of the Korean Peninsula..............................12
Japan’s International Reputation.............................13
Damage to Global Non-Proliferation Regime...................13

Japan’s Nuclear Future: Policy Debate,
Prospects, and U.S. Interests
The notion of Japan developing nuclear weapons has long been considered far-
fetched and even taboo, particularly within Japan. Hailed as an example of the
success of the international non-proliferation regime, Japan has consistently taken
principled stands on non-proliferation and disarmament issues. Domestically, the
largely pacifist Japanese public, with lingering memories of the destruction of
Hiroshima and Nagasaki by atomic bombs in the closing days of World War II, has
widely rejected any nuclear capacity as morally unacceptable. The inclusion of Japan
under the U.S. nuclear “umbrella,” with regular reiterations from U.S. officials,
provides a guarantor to Japanese security. Successive Japanese administrations and
commissions have concluded that Japan has little to gain and much to lose in terms
of its own security if it pursues a nuclear weapons capability.
Today, Japanese officials and experts remain remarkably uniform in their
consensus that Japan is unlikely to move toward nuclear status in the short-to-
medium term. However, as the security environment has shifted significantly, the
topic is no longer toxic and has been broached by several leading politicians. North
Korea’s test of a nuclear device in 2006 and China’s military modernization have
altered the strategic dynamics in the region, and any signs of stress in the U.S.-Japan
alliance raises questions among some about the robustness of the U.S. security
guarantee. An ascendant hawkish, conservative movement — some of whom openly
advocate for Japan to develop an independent nuclear arsenal — has gained more
traction in Japanese politics, moving from the margins to a more influential position.
In addition, previous security-related taboos have been overcome in the past few
years: the dispatch of Japanese military equipment and personnel to Iraq and
Afghanistan, the elevation of the Japanese Defense Agency to a full-scale ministry,
and Japanese co-development of a missile defense system with the United States. All
of these factors together increase the still unlikely possibility that Japan will
reconsider its position on nuclear weapons.
Any reconsideration of Japan’s policy of nuclear weapons abstention would
have significant implications for U.S. policy in East Asia. Globally, Japan’s
withdrawal from the Nuclear Non-Proliferation Treaty (NPT) could damage the most
durable international non-proliferation regime. Regionally, Japan “going nuclear”
could set off a nuclear arms race with China, South Korea, and Taiwan and, in turn,
India, and Pakistan may feel compelled to further strengthen their own nuclear
weapons capability. Bilaterally, assuming that Japan made the decision without U.S.
support, the move could indicate Tokyo’s lack of trust in the American commitment
to defend Japan. An erosion in the U.S.-Japan alliance could upset the geopolitical

balance in East Asia, a shift that could indicate a further strengthening of China’s
position as an emerging hegemonic power. These ramifications would likely be
deeply destabilizing for the security of the Asia Pacific region and beyond.
Japan’s post-war policy on nuclear weapons and non-proliferation has been to
reject officially a military nuclear program. The Japanese Army and Navy each
conducted nuclear weapons research during World War II, but neither was successful
in gaining enough resources for the endeavor.1 Despite the fact that by the early
1970s Japan had already acquired the technical, industrial and scientific resources
needed to develop its own nuclear weapons, Japanese policy has repeatedly stated its
opposition to the development of nuclear weapons.
Complicating Japan’s anti-nuclear weapons policy has been a post-World War
II dependence on the U.S. “nuclear umbrella” and security guarantee. Under the
terms of the Mutual Security Assistance Pact signed in 1952 and the 1960 Treaty of
Mutual Cooperation and Security, Japan grants the U.S. military basing rights on its
territory in return for a U.S. pledge to protect Japan’s security. The rejection of
nuclear weapons by the Japanese public appears to be overwhelmingly driven by
moral, rather than pragmatic, considerations, but Japan’s leaders have based their
policy of forswearing nuclear weapons on protection by the U.S. nuclear arsenal.
The bedrock of domestic law on the subject, the “Atomic Energy Basic Law”
of 1955, requires Japan’s nuclear activities to be conducted only for peaceful
purposes. In 1967, the “Three Non-Nuclear Principles” (hikaku sangensoku) were
announced by Prime Minister Eisaku Sato, enshrining the policy of not possessing,
not producing, and not permitting the introduction of nuclear weapons into Japan.
When Japan ratified the Nuclear Non-Proliferation Treaty (NPT) in 1976, it reiterated
its three non-nuclear principles, placed itself under the treaty obligation as a
non-nuclear weapons state, and pledged not to produce or acquire nuclear weapons.
Japan has been a staunch NPT supporter in good standing ever since.
Despite multiple reiterations of Japan’s non-nuclear status, this orthodoxy has
been challenged on several occasions, usually when Japan has felt strategic
vulnerability. Probably the most prominent episode occurred in the mid-1960s:
China tested a nuclear device for the first time in 1964, and the United States was
engaged in the Vietnam War. Prime Minister Eisaku Sato secretly commissioned
several academics to produce a study exploring the costs and benefits of Japan’s
possible nuclearization, the so-called “1968/70 Internal Report.”2 Another secret
investigation into Japan’s nuclear option was done by the Japan Defense Agency

1 Priority was placed on biological and chemical weapons programs. Kurt M. Campbell and
Tsuyoshi Sunohara, “Japan,” in Campbell, Einhorn, Reiss, eds., The Nuclear Tipping Point,
Brookings Institution Press, 2004; and Federation of American Scientists website.
[ h t t p : / / www.f a s .or g/ nuke / gu i d e / j a pa n/ nuke / ]
2 Yuri Kase, “The Costs and Benefits of Japan’s Nuclearization: An Insight into the 1968/70
Internal Report,” The Nonproliferation Review, Summer 2001.

(JDA) in 1995 as Japan assessed its standing in the new post-Cold War environment
after the 1994 North Korean nuclear crisis in 1994 and as the international
community was considering the indefinite extension of the NPT.3 Both reports
concluded that Japan should continue to rely on the U.S. security guarantee and that
development of nuclear weapons would threaten that relationship.
An Evolving Security Environment in Asia
Since the end of the Cold War, and particularly in the past decade, developments
in the region have increased Japan’s sense of vulnerability and caused some in the
policy community to rethink Japan’s policy of forswearing nuclear weapons
development. During the Cold War, the U.S. military presence in Japan represented
the Pacific front of containing the Soviets, a reassuring statement of commitment to
Japan’s security to many Japanese. North Korea’s test of a ballistic missile over
Japan in August 1998 dispelled the sense of a more secure post-Cold War
environment for the archipelago. Moreover, India and Pakistan both conducted
underground nuclear weapons tests earlier that year, which to many undermined the
success of the international non-proliferation regime and set off fears of a new
nuclear arms race. Japan was particularly alarmed at the tests, and instituted a freeze
on new loans and grants to the two states.
Since then, more provocative behavior from Pyongyang, particularly its 2006
tests of medium-range missiles and a nuclear device, have heightened Japan’s fear
of potential attacks. The nuclear test prompted prominent officials in the ruling party
to call for an open debate on whether to pursue nuclear arms: both Foreign Minister
Taro Aso and chairman of the party’s policy council called for such a debate before
later backing off their comments. In addition to North Korea’s activities, a proposed
U.S.-India civilian nuclear deal has led to concern among some Japanese non-
proliferation experts that the NPT has weakened further. To these experts, the
legitimacy and deterrent effect of the global non-proliferation regime underpins
Japan’s commitment to its own non-nuclear status.
While North Korea represents a more immediate danger, many defense experts
see China as the more serious and long-term threat to Japan’s security.4 China’s
rapid military modernization and advancements in weapons systems have
compounded Tokyo’s concern. Japanese defense papers have pointed to Beijing’s
apparent progress in short and medium range missiles, its submarine force (some of
which have on occasion intruded into Japan’s territorial waters), and nuclear force
modernization as specific areas of concern. As Chinese military spending continues
to accelerate, Japanese defense budgets have stagnated. Although Sino-Japanese
relations appear to have stabilized since a period of tension under former Prime
Minister Junichiro Koizumi’s administration, fundamental distrust and the potential
for conflict remains between the Pacific powers.

3 “‘95 Study: Japan and Nukes Don’t Mix,” The Asahi Shimbun, February 20, 2003.
4 Hajime Izumi and Katsuhisa Furukawa. “Not Going Nuclear: Japan’s Response to North
Korea’s Nuclear Test,” Nautilus Institute Policy Forum Online. July 19, 2007.

Japan’s Nuclear Capacity
Japan’s Nuclear Energy Program
Japan is a country poor in natural resources but with a high level of energy
consumption. Since the 1960s, Japan has relied on nuclear power for a significant
portion of its energy; nuclear energy currently provides 35% of its electricity. The
Japan Atomic Energy Commission’s 2005 Framework for Nuclear Energy Policy
emphasizes the importance of nuclear power for energy independence and carbon
emission reduction. Japan is currently the third-largest user of nuclear energy in the
world, with 55 light-water nuclear power reactors (49.58 million kW) operated by 10
electric power companies. The first commercial power reactor began operation in
1966. Two nuclear power plants are under construction, four are in the final stages
of regulatory review, and an additional seven may be built over the next decade.
Japan’s policy is to achieve a fully independent, or “closed,” fuel cycle.5 The
closed fuel cycle promotes the use of mixed-oxide (MOX) fuel in light-water
reactors. The set goal is to have 16-18 such reactors by FY2010, and utilities in Japan
are now in the process of being licensed for MOX loading and obtaining consent
from the local governments. The Japan Atomic Energy Agency (JAEA) was
established on October 1, 2005, to integrate Japan’s R&D institutes, the Japan
Atomic Energy Research Institute and the Japan Nuclear Cycle Development
Institute. JAEA carries out R&D work on the full range of fuel cycle activities.
Two of the more controversial aspects of Japan’s civilian power program are its
large stocks of separated plutonium and advanced fuel cycle facilities. Plutonium is
a by-product of the uranium fuel used in all nuclear reactors. Plutonium in spent fuel
is not weapons-usable. Once this reactor-grade6 plutonium is separated out of spent
fuel through reprocessing, it is potentially directly usable in nuclear weapons.7 This

5 Natural uranium ore first passes through the refining, conversion, enrichment, reconversion
and fabrication processes before it is fed into the nuclear reactor as a metal-sheathed fuel.
Following irradiation, the spent fuel from the reactor is sent to a reprocessing plant where
the residual uranium and newly produced plutonium are recovered for re-use as fuel. Then,
the plutonium oxide is mixed with uranium oxide at a MOX fuel conversion plant to
produce a mixed oxide nuclear fuel. MOX fuel can then be irradiated just like fresh fuel in
a nuclear power plant. This entire process is called the “closed” nuclear fuel cycle. See
[ ht t p: / / www.j a pannucl ear .com/ nucl e ar power / f uel c yc l e / what .ht ml ] .
6 Plutonium that contains at least 20 percent of the nonfissile isotopes Pu-240Reactor-grade
plutonium is 65% fissile (by thermal neutrons) compared with 93% fissile for weapon-
grade material.
7 Although reactor-grade plutonium has a higher-rate of spontaneous fission reactions and
therefore difficult to use in nuclear weapons, it was proven possible in a 1962 test. See U.S.
Congress, Office of Technology Assessment, “Technologies Underlying Weapons of Mass
Destruction,” December 1993; “Additional information concerning underground nuclear
weapon test of reactor-grade plutonium,”U.S. Department of Energy Office of Public Affairs
[https://www.osti.gov/opennet/document/press/pc29.htmll] and Richard L. Garwin,
“Reactor-Grade Plutonium Can be Used to Make Powerful and Reliable Nuclear Weapons,”

separated plutonium can also be “recycled” into MOX fuel for light-water power
reactors. France, India, Japan, Russia and the U.K. currently all produce reactor fuel
through reprocessing.
The global stockpile of separated plutonium is estimated to be about 500 tons,
including military and civilian stocks.8 Stocks of civilian separated plutonium are
growing around the world. According to the 2005 declared annual inventory under
IAEA INFCIRC/549, Japan possesses 5.9 MT of civilian stocks of separated
plutonium stored in Japan, and 37.9 MT of separated plutonium stored outside the
country.9 This material has the potential to make over 1,000 nuclear weapons.
Japan’s civilian separated plutonium stockpile is expected to grow to 70 tons by


To date, Japan has sent its spent fuel to the United Kingdom (Sellafield) and
France (La Hague) for reprocessing and MOX fuel fabrication. But Japan is
completing facilities which will eliminate the need for such outsourcing. The private
company Japan Nuclear Fuel Limited (JNFL) has built and is currently running active
testing on a large-scale commercial reprocessing plant at Rokkasho-mura, which is
expected to begin operating sometime in 2008. Its expected capacity is
800tons/year.11 A MOX fuel fabrication plant currently being built by JNFL at
Rokkasho-mura is expected to be completed in October 2012.
Around 2050, Japan plans to shift from MOX fuel in light water reactors to
using MOX fuel in fast breeder reactors.12 R&D work continues using the prototype
MONJU and JOYO fast breeder reactors, despite earlier accidents.13 A final disposal
site for high level radioactive waste has not yet been selected. Japan plans to store
and dispose of its nuclear waste domestically.14 Japan also has a uranium enrichment
R&D facility at Tokai-mura and is developing an advanced centrifuge uranium
enrichment plant at Rokkasho-mura.

7 (...continued)
August 1998 [http://www.fas.org/rlg/980826-pu.htm].
8 Global Fissile Material Report 2007, IPFM. [http://www.fissilematerials.org]
9 One metric ton is approximately 1.1 US tons.
10 Global Fissile Material Report 2007, IPFM. [http://www.fissilematerials.org]
11 A pilot reprocessing plant began full-scale operation in 1981 at the Tokai Nuclear Fuel
Cycle Engineering Laboratories.
12 A fast breeder reactor is a fast neutron reactor that produces more plutonium than it
consumes, which can then be reused as fuel in the reactor, thereby creating a closed fuel
13 The MONJU reactor’s operation was stopped due to a sodium leakage accident in the
reactor’s secondary system in 1995. During the course of manufacturing fuel for the JOYO
reactor, a Level-4 criticality accident occurred in September 1999 at a fuel conversion
14 For more on waste storage in Japan, see [http://www.japannuclear.com/nuclearpower/
program/ waste.html ].

The Rokkasho-mura reprocessing facility, the first in a non-nuclear weapon
state, has raised some proliferation concerns.15 Concerns have been raised in
particular over the construction of an industrial-scale reprocessing facility in Japan,.
Additionally, fast breeder reactors also produce more plutonium than they consume,
potentially posing a proliferation risk. Some cautionary voices point out that
advanced countries have been shifting away from the pursuit of reprocessing
technologies as the international community strives to find appropriate multilateral
approaches to containing the spread of enrichment and reprocessing technologies to
new countries.16
To counteract public concern, Japan emphasizes transparency in all aspects of
its nuclear activities to assure the public and international community that atomic
energy is used solely for peaceful purposes. All reactor operating electric power
utilities in Japan are required by law to make public the quantity of plutonium in
possession and a plutonium use plan each fiscal year. All of Japan’s nuclear facilities
are subject to IAEA full-scope safeguards, and an Additional Protocol to its IAEA
safeguards agreement came into force in December 1999. The protocol augments the
agency’s authority to verify that nuclear activities are not diverted to military
purposes. Japan has also been a leader in developing advanced safeguards
technologies with the IAEA, and participates in multilateral advanced research efforts
for future fuel cycle technologies, such as Generation IV International Forum
(Gen-IV), International Project on Innovative Nuclear Reactors and Fuel Cycles
(INPRO) and the U.S.-led Global Nuclear Energy Partnership (GNEP).17
Technological Potential
Japan’s technological advancement in the nuclear field, combined with its
stocks of separated plutonium, have contributed to the conventional wisdom that
Japan could produce nuclear weapons in a short period of time. In 1994, Prime
Minister Tsutomu Hata famously told reporters that “it’s certainly the case that Japan
has the capability to possess nuclear weapons but has not made them.” Indeed, few
dispute that Japan could make nuclear weapons if Tokyo were to invest the necessary
financial and other resources.
However, the ability to develop a few nuclear weapons versus the technological,
financial and manpower requirements of a full nuclear deterrent should be
considered. Producing nuclear weapons would require expertise on bomb design
including metallurgists and chemists; while a reliable deterrent capability may also

15 A nuclear weapon state as defined by the NPT is limited to states that have detonated a
nuclear weapon or nuclear explosive device before January 1, 1967. The United States,
United Kingdom, Russia, France, and China are the five nuclear weapon states under the
NPT. All other NPT parties are non-nuclear weapon states.
16 Since Japan has been in possession of this technology for decades, it does not fall into the
category of countries whose access to the technology might be limited in the future. See
CRS Report RL34234, Managing the Nuclear Fuel Cycle: Policy Implications of Expanding
Global Access to Nuclear Power, coordinated by Mary Beth Nikitin.
17 [http://www.gen-4.org/index.html], [http://www.iaea.org/OurWork/ST/NE/NENP/
NPTDS/Projects/INPRO/index.html], [http://www.gnep.energy.gov/]

require reliable delivery vehicles, an intelligence program to protect and conceal
assets from a first-strike, and a system for the protection of classified information.
The 1995 JDA report stated that Japan’s geography and concentrated populations
made the political and economic costs of building the infrastructure for a nuclear
weapons program “exorbitant.” If one assumes that Japan would want weapons with
high reliability and accuracy, then more time would need to be devoted to their
development unless a weapon or information was supplied by an outside source.
As some analysts have pointed out, if Japan manufactured nuclear warheads,
then it would need to at the minimum perform one nuclear test — but where this
could be carried out on the island nation is far from clear.18 Furthermore, Japan’s
nuclear materials and facilities are under IAEA safeguards, making a clandestine
nuclear weapons program difficult to conceal. The Rokkasho-mura reprocessing
plant was built in close consultation with the IAEA, with safeguards systems installed
in process lines during construction. Japan seems to have intentionally built its
nuclear program so it would not be ideal for military use, in compliance with
Japanese law.
Japanese Legal and Political Restraints
Domestic Factors
Public Opinion. In general, public opinion on defense issues in Japan appears
to be shifting somewhat, but pacifist sentiment remains significant. In the past,
Japanese public opinion strongly supported the limitations placed on the Japanese
military, but this opposition has softened considerably since the late 1990s. Despite
this overall shifting tide, the “nuclear allergy” among the general public remains
strong. The devastation of the atomic bombings led Japanese society to recoil from
any military use of nuclear energy. Observers say that the Japanese public remains
overwhelmingly opposed to nuclearization, pointing to factors like an educational
system that promotes pacifism and the few surviving victims of Hiroshima and
Nagasaki who serve as powerful reminders of the bombs’ effects.
While Japanese public opinion remains, by most accounts, firmly anti-nuclear,
some social currents could eventually change the conception of nuclear development.
Many observers have recognized a trend of growing nationalism in Japan,
particularly among the younger generation. Some Japanese commentators have
suggested that this increasing patriotism could jeopardize closer cooperation with the
United States: if Japan feels too reliant on U.S. forces and driven by U.S. priorities,
some may assert the need for Japan to develop its own independent capability.
Another wild card is the likelihood that Japan will face a major demographic
challenge because of its rapidly ageing population: such a shock could either drive
Japan closer to the United States because of heightened insecurity, or could spur
nationalism that may lean toward developing more autonomy.

18 Tetsuya Endo, “How Realistic Is a Nuclear-Armed Japan?,” AJISS-Commentary No. 8,
July 20, 2007.

Elite Opinions. A review of recent articles and interviews with prominent
Japanese opinion-makers and experts revealed a near-consensus of opposition to the19
development of nuclear weapons. Realist-minded security observers cite the danger
of threatening China and causing unnecessary instability in the region, while foreign
policy managers point to the risk of weakening the U.S. alliance. Some observers
claim, however, that a younger generation of upcoming elites may be more
nationalistic and therefore potentially more supportive of the option in the future.
There is some degree of disagreement in Japan on if a debate itself about
whether Japan should consider the nuclear option would be a valuable exercise.
Some nuclear critics argue that such a debate would solidify Japan’s non-nuclear
stance by articulating for the public why not possessing nuclear weapons serves the
national interest. The debate could also reassure those who oppose Japan’s nuclear
development. Others, however, argue that simply raising the issue would alarm
Japan’s neighbors, arouse distrust, and negatively affect regional security.
Domestically, some analysts think that a public debate on nuclear weapons would
outrage the Japanese public, making most politicians averse to the proposal.
Constitutional Restraints. There are several legal factors that could restrict
Japan’s ability to develop nuclear weapons. The most prominent is Article 9 of the
Japanese constitution, drafted by American officials during the post-war occupation,
that outlaws war as a “sovereign right” of Japan and prohibits “the right of
belligerency.” However, Japan maintains a well-funded and well-equipped military
for self-defense purposes, and the current interpretation of the constitution would
allow, in theory, the development of nuclear weapons for defensive purposes.
Beginning with Prime Minister Nobusuke Kishi in 1957, and continuing through
Shinzo Abe in 2006, Japanese administrations have repeatedly asserted that Article
9 is not the limiting factor to developing nuclear weapons.20 As Chief Cabinet
Secretary in 2002, current Prime Minister Yasuo Fukuda said that the constitution did
not prohibit nuclear weapons, adding that “depending upon the world situation,
circumstances and public opinion could require Japan to possess nuclear weapons.”21
1955 Atomic Energy Basic Law. Although the Constitution may be
interpreted to allow for possession of nuclear weapons, since 1955 Japanese domestic
law prohibited any military purpose for nuclear activities.22 Its basic policy statement
(Article 2) says: “the research, development, and utilization of atomic energy shall
be limited to peaceful purposes, aimed at ensuring safety and performed
independently under democratic management, the results therefrom shall be made
public to contribute to international cooperation.” This law, which also established

19 According to a series of interviews carried out in Tokyo in February 2007 as well as
articles such as Hajime Izumi and Katsuhisa Furukawa. “Not Going Nuclear: Japan’s
Response to North Korea’s Nuclear Test,” Arms Control Today, Volume 37, Issue 6. July

1, 2007.

20 Llewelyn Hughes, “Why Japan Will Not Go Nuclear (Yet),” International Security, Vol.

31, No. 4. Spring 2007.

21 “So Much for Japan’s Nuclear Taboo,” International Herald Tribune. June 13, 2002.
22 [http://www.jaea.go.jp/jnc/kaihatu/hukaku/english/atomiclaw.htm]

regulatory bodies for safety and control issues, is at the core of Japanese policy in
maintaining a peaceful, transparent nuclear program.
Three Non-Nuclear Principles. Japanese leaders have often cited the
“Three Non-Nuclear Principles” as another obstacle to Japanese development of
nuclear weapons. The trio consists of Japanese pledges not to allow the
manufacture, possession, or importation of nuclear weapons. Many security experts,
however, point out that the principles, passed as a Diet resolution in 1971 as part of
domestic negotiations over the return of Okinawa from U.S. control, were never
formally adopted into law, and therefore are not legally binding.23 Although not
technically a legal constraint, Japanese leaders have consistently stated their
commitment to the principles, including a reiteration by Prime Minister Shinzo Abe
in the aftermath of North Korea’s nuclear test in 2006.
External Factors
International Law. Japan is obligated under Article 2 of the NPT not to
“receive the transfer from any transferor whatsoever of nuclear weapons or other
nuclear explosive devices or of control over such weapons or explosive devices
directly, or indirectly; not to manufacture or otherwise acquire nuclear weapons or
other nuclear explosive devices; and not to seek or receive any assistance in the
manufacture of nuclear weapons or other nuclear explosive devices.” Under Article
3 of the NPT, Japan is required to accept IAEA full-scope safeguards on its civilian
nuclear program. Japan signed an Additional Protocol in 1998 under which the IAEA
can use an expanded range of measures to verify that civilian facilities and materials
have not been diverted to a military program.
Consequences for Civilian Nuclear Program. Lacking adequate
indigenous uranium supplies, Japan has bilateral civilian nuclear cooperation
agreements with the United States, France, United Kingdom, China, Canada, and
Australia. If a Japanese nuclear program for military purposes were declared or
discovered, Japan would need to return the supplied material to its country of origin.
Japan’s civilian nuclear energy program — which supplies over a third of Japan’s
energy — would then be cut off from world supplies of natural uranium, enriched
uranium and related equipment.
The United States most recent nuclear energy cooperation agreement with Japan
took effect on July 17, 1988. Article 12 of this agreement states that, if either party
does not comply with the agreement’s nonproliferation provisions or violates their
IAEA safeguards agreement, the other party has the right to cease further
cooperation, terminate the agreement, and require the return of any material, nuclear
material, equipment or components transferred or “any special fissionable material
produced through the use of such items.”
If Japan withdrew from the NPT, it would likely be subject to UN Security
Council-imposed sanctions and economic and diplomatic isolation. Penalties under

23 Llewelyn Hughes, “Why Japan Will Not Go Nuclear (Yet),” International Security, Vol.

31, No. 4. Spring 2007.

a U.N. Security Council resolution could include economic sanctions beyond the
Nuclear Suppliers Group cut-off of nuclear-related supply.
International Diplomatic Consequences. Diplomatically, the policy turn-
about would have profound implications. Japan has built a reputation as a leader in
non-proliferation and as a promoter of nuclear disarmament. It has consistently called
for a “safe world free of nuclear weapons on the earliest possible date.” Japan
submits a resolution to the General Assembly’s First Committee each year on a
nuclear-free world and submits working papers to the NPT review conferences and
preparatory committees on disarmament. It has been a vocal advocate for IAEA
verification and compliance and was the first to respond with sanctions to nuclear
tests in South Asia and North Korea. It has been a constant voice in support of
nuclear disarmament in international fora. An about-face on its non-nuclear weapon
state status would dramatically change the global view of Japan, or might
dramatically change the perception of nuclear weapons possession in the world. This
move could have profound implications for nuclear proliferation elsewhere, perhaps
leading to additional NPT withdrawals. Acquiring nuclear weapons could also hurt
Japan’s long-term goal of permanent membership on the UN Security Council.
Issues for U.S. Policy
U.S. Security Commitment. Perhaps the single most important factor to
date in dissuading Tokyo from developing a nuclear arsenal is the U.S. guarantee to
protect Japan’s security. Since the threat of nuclear attack developed during the Cold
War, Japan has been included under the U.S. “nuclear umbrella,” although some
ambiguity exists about whether the United States is committed to respond with
nuclear weapons in the event of a nuclear attack on Japan.24 U.S. officials have
hinted that it would: following North Korea’s 2006 nuclear test, Secretary of State
Condoleezza Rice, in Tokyo, said, “...the United States has the will and the capability
to meet the full range, and I underscore full range, of its deterrent and security
commitments to Japan.”25
During the Cold War, the threat of mutually assured destruction to the United
States and the Soviet Union created a sort of perverse stability in international
politics; Japan, as the major Pacific front of the U.S. containment strategy, felt
confident in U.S. extended deterrence. Although the United States has reiterated its
commitment to defend Japan, the strategic stakes have changed, leading some in
Japan to question the American pledge. Some in Japan are nervous that if the United
States develops a closer relationship with China, the gap between Tokyo’s and
Washington’s security perspectives will grow and further weaken the U.S.
commitment.26 These critics also point to what they perceive as the soft negotiating
position on North Korea’s denuclearization in the Six-Party Talks as further evidence

24 Hajime Izumi and Katsuhisa Furukawa, “Not Going Nuclear: Japan’s Response to North
Korea’s Nuclear Test,” Nautilus Institute Policy Forum Online. July 19, 2007.
25 “U.S. Is Japan’s Nuclear Shield, Rice Says,” Los Angeles Times. October 19, 2006.
26 Brad Glosserman, “Japan Peers Into the Abyss,” PacNet Newsletter #20. March 20, 2008.

that the United States does not share Japan’s strategic perspective.27 A weakening
of the bilateral alliance may strengthen the hand of those that want to explore the
possibility of Japan developing its own deterrence.
Despite these concerns, many long-time observers assert that the alliance is
fundamentally sound from years of cooperation and strong defense ties throughout
even the rocky trade wars of the 1980s. Perhaps more importantly, China’s rising
stature likely means that the United States will want to keep its military presence in
the region in place, and Japan is the major readiness platform for the U.S. military
in East Asia. If the United States continues to see the alliance with Japan as a
fundamental component of its presence in the Pacific, U.S. leaders may need to
continue to not only restate the U.S. commitment to defend Japan, but to engage in
high-level consultation with Japanese leaders in order to allay concerns of alliance
drift. Congressional leaders could face pressure to re-consider allowing the sale of
the F-22 Raptor aircraft in order to bolster trust in the alliance.28
U.S. behavior plays an outsized role in determining Japan’s strategic
calculations, particularly in any debate on developing nuclear weapons. Security
experts concerned about Japan’s nuclear option have stressed that U.S. officials or
influential commentators should not signal to the Japanese any tacit approval of
nuclearization.29 Threatening other countries with the possibility of Japan going
nuclear, for example, could be construed as approval by some quarters in Tokyo.
U.S.-Japanese joint development of a theater missile defense system reinforces
the U.S. security commitment to Japan, both psychologically and practically. The
test-launch of several missiles by North Korea in July 2006 accelerated existing plans
to jointly deploy Patriot Advanced Capability 3 (PAC-3) surface-to-air interceptors
as well as a sea-based system on Aegis destroyers. If successfully operationalized,
confidence in the ability to intercept incoming missiles may help assuage Japan’s fear
of foreign attacks. This reassurance may discourage any potential consideration of
developing a deterrent nuclear force. In addition, the joint effort would more closely
intertwine U.S. and Japan security, although obstacles still remain for a seamless

27 Brad Glosserman, “Nuclear Basics for the Alliance,” PacNet Newsletter #21. April 19,


28 For more information, see CRS Report RS22684, Potential F-22 Raptor Export to Japan,
by Christopher Bolkcom and Emma Chanlett-Avery.
29 Kurt Campbell and Tsuyoshi Sunohara, “Japan: Thinking the Unthinkable,” The Nuclear
Tipping Point, 2004.
30 The principle of “collective self-defense” raises questions about how closely the United
States and Japan can integrate missile defense cooperation. The term comes from Article
51 of the U.N. Charter, which provides that member nations may exercise the rights of both
individual and collective self-defense if an armed attack occurs. The Japanese government
maintains that Japan has the sovereign right to engage in collective self-defense, but a 1960
decision by the Cabinet Legislation Bureau interpreted the constitution to forbid collective
actions because it would require considering the defense of other countries, not just the
safety of Japan itself. The ban on collective self-defense raises questions about how

Potential for Asian Arms Race. To many security experts, the most
alarming possible consequence of a Japanese decision to develop nuclear weapons31
would be the development of a regional arms race. The fear is based on the belief
that a nuclear-armed Japan could compel South Korea to develop its own program;
encourage China to increase and/or improve its relatively small arsenal; and possibly
inspire Taiwan to pursue nuclear weapons. This in turn might have spill-over effects
on the already nuclear-armed India and Pakistan. The prospect — or even reality —
of several nuclear states rising in a region that is already rife with historical
grievances and contemporary tension could be deeply destabilizing. The counter-
argument, made by some security experts, is that nuclear deterrence was stabilizing
during the Cold War, and a similar nuclear balance could be achieved in Asia.
However, most observers maintain that the risks outweigh potential stabilizing
U.S.-China Relations. The course of the relationship between Beijing and
Washington over the next several years is likely to have a significant impact on the
nuclearization debate in Japan. If the relationship chills substantially and a Cold
War-type standoff develops, there may be calls from some in the United States to
reinforce the U.S. deterrent forces. Some hawkish U.S. commentators have called
for Japan to be “unleashed” in order to counter China’s strength.32 Depending on the
severity of the perceived threat from China, Japanese and U.S. officials could
reconsider their views on Japan’s non-nuclear status. Geopolitical calculations likely
would have to shift considerably for this scenario to gain currency. On the other
hand, if U.S.-Sino relations become much closer, Japan may feel that it needs to
develop a more independent defense posture. This is particularly true if the United
States and China engaged in any bilateral strategic or nuclear consultations.33
Despite improved relations today, distrust between Beijing and Tokyo remains
strong, and many in Japan’s defense community view China’s rapidly modernizing
military as their primary threat.
Future of the Korean Peninsula. Any eventual reunification of the Korean
peninsula could further induce Japan to reconsider its nuclear stance. If the two
Koreas unify while North Korea still holds nuclear weapons and the new state opts
to keep a nuclear arsenal, Japan may face a different calculation. Indeed, some

30 (...continued)
Japanese commanders will gauge whether American forces or Japan itself is being targeted.
Under the current interpretation, Japanese forces could not legally respond if the United
States were attacked.
31 Masahiro Matsumura, “Prudence and Realism in Japan’s Nuclear Options,” Brookings
Institution website, January 16, 2008.
32 See Richard Lowry, “Time for the Sun to Rise,” National Review. July 4, 2005.
33 Katsuhisa Furukawa, “Japanese Perspectives on Nuclear Weapons, Disarmament, and
Nonproliferation,” Research Institute of Science and Technology for Society powerpoint
presentation. November 29, 2007. For more on existing U.S.-PRC nuclear cooperation, see
CRS Report RL33192, U.S.-China Nuclear Cooperation Agreement, coordinated by Shirley

Japanese analysts have claimed that a nuclear-armed reunified Korea would be more
of a threat than a nuclear-armed North Korea.
Such a nuclear decision would depend on a variety of factors: the political
orientation of the new country, its relationship with the United States, and how a
reunified government approached its historically difficult ties with Japan. Although
South Korea and Japan normalized relations in 1965, many Koreans harbor
resentment of Japan’s harsh colonial rule of the peninsula from 1910-1945. If the
closely neighboring Koreans exhibited hostility toward Japan, it may feel more
compelled to develop a nuclear weapons capability. The United States is likely to be
involved in any possible Korean unification because of its military alliance with
South Korea and its leading role in the Six-Party Talks. U.S. contingency planning
for future scenarios on the Korean peninsula should take into account Japan’s
calculus with regard to nuclear weapon development.
Japan’s International Reputation. If Japan decided to go nuclear, its
international reputation as a principled advocate for non-proliferation would erode.
Many observers say this would rule out Japan’s ambition of eventually holding a seat
on the United Nations Security Council. Japan, of course, would bear the brunt of
these consequences, but it could be harmful to U.S. interests as well. Japan is
generally viewed overwhelmingly positively by the international community, and its
support for U.S.-led international issues can lend credibility and legitimacy to efforts
such as democracy promotion, peacekeeping missions, environmental cooperation,
and multilateral defense exercises, to name a few.
Damage to Global Non-Proliferation Regime. Japan’s development of
its own nuclear arsenal could also have damaging impact on U.S. nonproliferation
policy. It would be more difficult for the United States to convince non-nuclear
weapon states to keep their non-nuclear status or to persuade countries such as North
Korea to give up their weapons programs. The damage to the NPT as a guarantor of
nuclear power for peaceful use and the IAEA as an inspection regime could be
irreparable if Japan were to leave or violate the treaty. If a close ally under its nuclear
umbrella chose to acquire the bomb, perhaps other countries enjoying a strong
bilateral relationship with the United States would be less inhibited in pursuing their
own option. It could also undermine confidence in U.S. security guarantees more