The Japan Institute of International Affairs

How Realistic Is a Nuclear-Armed Japan?
Tetsuya Endo 20 July 2007
Whether Japan should go nuclear is a long-standing question. The country has seen several waves of heated debates on this issue in past decades, beginning in 1960 when Japan revised and renewed the Security Treaty with the United States. The debate was revived shortly after China conducted its first nuclear weapons test in 1964, and this carried over well into the 1970s, when Japan mulled whether to join the international nonproliferation regime (Japan signed the NPT in 1970, but delayed ratification for six years). The North Korean nuclear test in October last year fuelled the latest wave of the nuclear debate, which was more intense than ever. Yet the question of a nuclear-armed Japan has been raised more often abroad than within Japan.

The pros and cons of a nuclear Japan aside, how feasible is it for Japan to acquire nuclear weapons? Many of the past debates have centered on security considerations and little attention has been paid to technological aspects and the international framework concerning nuclear energy. I hope to examine the latter aspects by taking into account as broad a range of issues as possible.


Technologically, Japan is capable of developing nuclear weapons if it invests considerable time and money. A major nuclear energy user possessing 55 nuclear reactors and committed to its nuclear fuel cycle program, Japan possesses high-level nuclear technologies, a substantial amount of plutonium and the capability to enrich uranium. Although nearly all this plutonium is reactor-grade plutonium unsuitable for nuclear explosion, Japan does possess a small amount of high-grade plutonium. A majority of its uranium is low-enriched, but Japan is capable of producing highly-enriched uranium if it wishes. Japan indeed retains highly-enriched uranium for use in research and experiments, albeit in an extremely small amount. Nevertheless, it is virtually unthinkable for this country to divert nuclear fuel to make bombs in secret. Its plutonium and uranium are kept under strict IAEA verification, and Japan is a highly transparent society. Even if Japan succeeds in manufacturing nuclear warheads, where is it going to test them? Some people say simulation technology can substitute for an onsite test, but the first nuclear warhead at least would require an onsite test. However, there is no geographically suitable place for such a test in Japan.

Given time, it is not technologically impossible for Japan to develop nuclear weapons as well as their delivery systems. However, developing more than one or two nuclear bombs would require enormous money. There is a huge gap between possessing the technology to produce one or two nuclear bombs and arming oneself with nuclear weapons "effectively".

What about the legal and policy aspects? Article 9 of the Constitution makes no mention of nuclear weapons, and the Japanese government has established an interpretation that the Constitution does not prohibit Japan from possessing nuclear weapons as long as they are retained for exclusively self-defensive purposes. In practice, though, the 1955 Atomic Energy Basic Law, which regulates Japan's nuclear activities, limits the use of atomic energy to peaceful purposes alone and bans research and development for other purposes, including weapons production. Successive governments have also adhered to the three non-nuclear principles of not possessing, not producing and not permitting the introduction of nuclear weapons into Japan, which were incorporated into a parliamentary resolution. Although the non-nuclear principles are not legally binding, they have become an important pillar of Japan's national policy. People may suspect that such domestic arrangements could be overturned through legal or administrative procedures. Given the strong anti-nuclear sentiment among the Japanese people, however, this will not happen so easily.

International Restraints

Greater restraints on a nuclear-armed Japan come from abroad than from within. Japan will be faced with severe economic and political risks if it ignores international restraints and embarks on the development of nuclear weapons.

The first restraint is the Nuclear Nonproliferation Treaty. To arm itself with nuclear weapons, Japan would have to withdraw from this international nonproliferation regime. The withdrawal of a major nuclear energy user could trigger a domino effect worldwide, dealing a serious blow to the already shaken nonproliferation regime. The consequences of becoming internationally isolated are shown all too clearly by Japan's diplomatic situation starting from the 1930s.

The second is the possible suspension or termination of bilateral nuclear cooperation agreements that Japan has concluded with countries such as the United States, France, Britain, Canada, and Australia. These agreements ensure steady supplies to Japan of natural uranium, enriched uranium and nuclear energy technologies among other things on condition that Japan use the supplied material and technologies strictly for peaceful purposes. As soon as it is discovered that Japan has diverted them to weapons development, Japan will not only see its supplies of nuclear fuel cut off but will also be required to return all the material provided theretofore. This will lead to a virtual suspension of all nuclear activities in Japan, causing serious economic damage to a country in which nuclear energy accounts for a third of total power generation.

Japan's acquisition of nuclear weapons would have a grave impact on international politics as well. The Japan-US security alliance, which sits at the very foundation of Japan's national security policy, includes a US nuclear umbrella over Japan (extended deterrence). Behind the domestic argument that Japan should arm itself with nuclear weapons lie suspicions about the efficacy of this nuclear umbrella. However, such suspicions only beget US distrust in Japan, which might bring about a drastic change in the nature of the Japan-US alliance. Would the US permit Japan to go nuclear in the first place? I think this is hardly possible given the US attitude toward the NPT system as well as past examples of Japan-US negotiations on nuclear energy.

The development of nuclear weapons by Japan would seriously damage its relations with its neighbors. More than half a century has passed since World War II came to an end, but Japan's relations with Asian countries remain still sensitive. The thought of Japan going nuclear would evoke nightmares of the past in these countries. At any rate, a nuclear-armed Japan would fuel fear among its neighbors and destabilize the region.

As the sole nation to suffer a nuclear attack, Japan has advocated the elimination of nuclear weapons throughout its postwar history and has made nuclear disarmament, including the complete banning of nuclear tests, an important pillar of its diplomacy. In addition to its own non-nuclear policy, Japan has proactively cooperated in global efforts against nuclear proliferation. A turnabout in its nuclear policy would disrupt Japan's diplomatic consistency and seriously undermine its diplomatic principles.

As I mentioned above, Japan has the technology to develop nuclear weapons and, with the relevant legal revisions, Japan could actually embark on a nuclear weapons development program. Developing its own nuclear weapons is by no means impossible for Japan. However, it would require huge commitments of manpower, material and money, and it would not be so easy to change the persisting popular anti-nuclear sentiment. More importantly, a nuclear-armed Japan would face severe isolation from the international community. Given all these grave risks, it is clear that the nuclear option is surely not in the national interest of Japan and far from a realistic policy choice.

Tetsuya Endo is Senior Adjunct Fellow of The Japan Institute of International Affairs and a former vice chairman of the Atomic Energy Commission of Japan.

The views expressed in this piece are the author's own and should not be attributed to The Association of Japanese Institutes of Strategic Studies.
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