Article in Politics / International / Asia & Pacific Rim
Japan has one of the world’s most advanced civil nuclear technologies. Until recently, it was generally thought to be extremely unlikely to take the political decision to become a nuclear-weapon power. No longer on the margins in Japanese politics, the nuclear issue is gaining momentum.

The use of nuclear-power reactors to generate electricity is increasing as countries are turning to nuclear energy to improve the security of their energy supplies and because they are increasingly concerned about the adverse consequences of global warming. Nuclear power emits somewhat less carbon dioxide, a greenhouse gas, than energy sources that rely on the burning of fossil fuels.

The increasing use of nuclear energy – the so-called nuclear renaissance – will spread civil nuclear technology to more and more countries, technology that can be used to make nuclear weapons. More than 45 countries are actively considering the use of nuclear energy and this number may well grow (1). These countries will, in the foreseeable future, be able to produce the fissile material needed for nuclear weapons; they will also have the nuclear physicists and nuclear engineers needed to design and make them. Because they could become actual nuclear-weapon powers in a relatively short time – months rather than years – they are known as ‘latent’ nuclear-weapon powers.

Today, the world contains nine actual nuclear-weapon powers. China, France, Russia, the UK, and the USA are well-established ones. India, Israel and Pakistan have significant nuclear arsenals. And North Korea almost certainly has a small number of nuclear weapons. Many think that Iran intends to acquire them.

Japan is a, if not the, leading latent nuclear-weapon power. It has stocks of plutonium, and the capability to produce highly-enriched uranium, that could be used in nuclear weapons and the nuclear personnel needed to produce them.

Until recently, Japan, with its largely pacifist public, was generally thought to be extremely unlikely to take the political decision to become a nuclear-weapon power. For several decades after the Second World War the lingering memories of the destruction of Hiroshima and Nagasaki by nuclear weapons made the idea that Japan would itself develop nuclear weapons appear outrageous and far-fetched. The Japanese public rejected the acquisition of nuclear weapons as morally repugnant. Within Japan the subject was taboo. And Japan has long been one of the world’s strongest supporters of nuclear non-proliferation and nuclear disarmament.

Since 1945, Japan has been sheltered by the American nuclear “umbrella” which provides a guarantee of Japanese security (2). The security situation has, however, recently changed significantly and the nuclear topic, no longer so toxic, has been raised by several leading politicians. A number of events account for the change. North Korea’s two tests of nuclear weapons, in 2006 and 2009; North Korean tests of ballistic missiles; and China’s modernization of its military forces, are among the factors that have considerably altered the strategic equation in the Asia-Pacific region.

Moreover, many post-Second World War security problems remain unresolved. The Korean peninsula remains divided; the United States is still the predominant military power in the region; and nationalism remains a powerful force in China, Japan, North Korea and South Korea. These alone should cause major concern for the future peace and stability of the region. But the threats to peace in the region could soon get worse.

One of these threats arises from Japan’s own nuclear and ballistic-missile capabilities, capabilities which have been acquired not by accident but design. Deliberate policy, set in motion by senior politicians in the late 1960s, was aimed at acquiring them. Through both a civil nuclear-energy programme, based on the production and use of plutonium as a nuclear fuel, and an active commercial space programme, using several types of solid-fuel rockets, successive Japanese governments have achieved the desired nuclear capability and the basis for a long-range ballistic missile programme (3).

From time to time, questions are raised within Japan about the strength of the American security guarantee and how long it can be expected to last. Moreover, domestic Japanese politics have moved to the right, with some hawks publicly arguing that Japan should develop an independent nuclear arsenal. Some right-wing American commentators would also like to see Japan go nuclear so that it shares the burden of providing security in the Asia-Pacific region. No longer on the margins in Japanese politics, the nuclear issue is gaining momentum.

Japan’s Civil Nuclear Programme

Japan has very advanced civil nuclear technology – one of the world’s most advanced. The fact that Japan needs to import some 80% of its energy requirements explains its interest in nuclear power. The country's 55 nuclear-power reactors (4) provide some 30% of the country's electricity and this is expected to increase to at least 40% by 2017. Currently (end of 2010), these reactors generate about 38,875 megawatts of electricity (MWe), making Japan the world’s third largest producer of nuclear electricity, after the USA and France (5).

Japan has had a great deal of experience in all aspects of nuclear reactor technology. It began research in nuclear technology in 1954, just nine years after the end of the Second World War. The Atomic Energy Commission, established in 1956 (under the 1955 Atomic Energy Basic Law), energetically promoted the development and use of nuclear power for electricity generation.

The Japan’s first civil nuclear power reactor, the Tokai-1 reactor, was sold to it by the United Kingdom; it began operating in July 1966 and operated for 22 years, until March 1988. In 1970, Japan began constructing nuclear-power reactors in earnest.

By the end of the 1970s, industrial giants such as Hitachi, Toshiba and Mitsubishi had developed the capability to design and construct light-water reactors, both Pressurised Water Reactors (PWRs) and Boiling Water Reactors (BWRs), including reactors with generating capacity of up to 1,400 MWe. Japan now exports nuclear reactors to other Asian countries and develops new reactor designs, such as the Advanced BWR (ABWR). Two ABWRs are in commercial operation and two more are under construction. Japan is well placed to benefit commercially from the nuclear renaissance.

Apart from designing and constructing reactors, Japan is operating all the other elements of the complete nuclear fuel cycle except uranium mining. Having no uranium that can be mined economically, it imports yellow cake and has industrial plants to convert and enrich uranium and to fabricate reactor fuel elements.

It is operating a commercial reprocessing plant at Rokkasho-Mura, Aomori, operated by Japan Nuclear Fuel Limited (JNFL) (3). A reprocessing plant separates the unused uranium, the plutonium inevitably produced as the reactor consumes uranium fuel, and fission products.

The Rokkasho-Mura Reprocessing Plant (RRP), with an operating capacity of 800 tonnes of spent nuclear power reactor fuel per year, is the world’s most up-to-date reprocessing plant. The output of RRP is not the usual plutonium dioxide, but plutonium dioxide mixed with uranium dioxide, or MOX. But the plutonium dioxide and the uranium dioxides could be separated by straightforward chemistry. The plutonium dioxide could then be converted to plutonium that could be used in nuclear weapons. Japan plans to use eventually commercial fast breeder reactors (FBRs) fuelled by plutonium.

Japan has a large stockpile of civil plutonium. According to a declaration that Japan made to the International Atomic Energy Agency (IAEA), as of 31 December 2009, it owned 4,400 kg of separated unirradiated plutonium at its reprocessing facilities, 1,900 kg in unirradiated MOX fuel, 3,300 kg in the MOX fuel manufacturing process, and 24,100 kg of unirradiated plutonium outside of its territory. It is estimated that Japan’s stockpile on current trends will reach 145 tonnes by 2020 (3). For comparison, today’s total world stock of civil plutonium is about 250 tonnes.

In addition, Japan already has a stockpile of plutonium that could be used directly to fabricate nuclear weapons. About 444 kilograms of this plutonium are in critical assemblies at Tokai-Mura, Ibaraki, plutonium of the type preferred by nuclear-weapon designers to fabricate the most effective nuclear weapons. There is enough to produce more than 100 nuclear weapons.

A critical assembly is designed for studying structures that contain fissile materials (plutonium or highly enriched uranium) in a configuration and quantity sufficient for realization of a nuclear fission chain reaction. Such experiments are necessary for checking the correctness of calculations relevant to nuclear reactors and to nuclear weapon components.

Japan could, if it chose to do so, also use its reactor-grade plutonium, separated from spent nuclear-power reactor fuel element, to produce nuclear weapons. For an advanced technological country like Japan, reactor-grade plutonium is just as good as weapon-grade plutonium to produce nuclear weapons (6). Some argue that it is better because a nuclear weapon made using reactor-grade plutonium would not need a neutron gun to initiate the fission process (7).

Japan’s FBR Programme

Japan has been interested for some time in developing FBRs. These reactors differ from other types in that they produce more fuel than they consume. Uranium-238 in the core of the reactor and in a ‘blanket’ placed around the core is converted into plutonium-239.

The plutonium can be used to fuel another breeder so that enough nuclear fuel becomes available not only to keep the reactor going but also to fuel a new one of the same size. Eventually, a family of breeder reactors becomes self-sustaining in nuclear fuel, requiring only a relatively small annual replenishment of uranium-238. FBRs are obviously attractive to Japan because it has no significant indigenous supplies of uranium. The plutonium recovered from a FBR run in an optimum way is precisely the type of plutonium needed to fabricate the most effective nuclear weapons.

Japan has two FBRs. The Joyo experimental FBR has been operating since 1977 at Ōarai, Ibaraki. The Monju prototype FBR started up, in Tsuruga, Fukui Prefecture, in April 1994 but it has not operated since December 1995 when a sodium leak occurred and it had to be shut down. In August 2010, a device accidentally fell into the Monju reactor and the task of removing it will delay its full start-up until 2014 or later. The reactor will then have been shut down for 19 years.

The Evolution of a Nuclear-Weapon Programme

The first stages in a nuclear-weapon programme involve designing a nuclear weapon, using available open and covert data, and performing feasibility studies of possible designs. These stages use paper and computer studies and some proto-type testing but are not directed towards the production of nuclear weapons.

It would be very surprising, to say the least, if Japan had not worked on these initial stages. They have probably been initiated without a decision by the political leadership but one by defence bureaucrats. But political leaders will almost certainly be involved in any decision to move to the development and production stages of a nuclear-weapon programme.

Japan’s political leadership may take such a decision perhaps after discussion with a small number of colleagues but it may not involve the entire senior political group, such as the whole cabinet. If Japan takes the political decision to fabricate nuclear weapons, it will almost certainly use plutonium-239 as the fissile material and the implosion method to fabricate its first nuclear weapons. (The implosion method was developed by the Americans during the Second World War in the Manhattan Project and used to explode the atomic bomb that destroyed Nagasaki in August 1945.)


If Japan does decide to go nuclear, history shows that the world will soon learn to live with the decision. After India and Pakistan, for example, conducted their nuclear weapons tests in 1998, sanctions were applied by various countries, including Japan. But Indian and Pakistani relations with their allies, like the United States and Japan, very soon recovered and then even improved.

The reality, clear for all to see, is that India and Pakistan have thrived in the aftermath of their becoming nuclear-weapon powers. India has signed very favourable nuclear-cooperation agreements with the United States and Pakistan has taken delivery of American F-16 combat aircraft that are able to deliver nuclear weapons. If India and Pakistan can get away with it, then Japan can too, particularly given Japan's strategic importance to the United States.

But the consequences of Japan going nuclear would be very serious for global security and for security in the Asia-Pacific region. Pressure in South Korea to follow suit and acquire nuclear weapons would be huge; relations with China could deteriorate dramatically; and the international nuclear non-proliferation regime, based on the Non-Proliferation Treaty (NPT), would be so badly damaged that it probably would not recover.


1. Emerging Nuclear Energy Countries, World Nuclear Power Reactors 2009-10, 7 December 2010

2. Emma Chanlett-Avery and Mary Beth Nikitin, Japan's Nuclear Future: Policy Debate, Prospects, and U.S. Interests, Congressional Research Service, February 19, 2009.

3. Frank Barnaby and Shaun Burnie, Thinking the Unthinkable: Japanese nuclear power and proliferation in East Asia, Oxford Research Group and Citizens’ Nuclear Information Center, Oxford and Tokyo, 2005,

4. World Nuclear Association, World Nuclear Power Reactors and Uranium Requirements

5. Nuclear Power in Japan

6. J. Carson Mark, Explosive Properties of Reactor-Grade Plutonium, Science and Global Security, Vol.4, pp.111-128, 1993 and Richard L. Garwin, Reactor-Grade Plutonium Can be Used to Make Powerful and Reliable Nuclear Weapons: Separated plutonium in the fuel cycle must be protected as if it were nuclear weapons, Federation of American Scientists, August 26, 1998.

7. Bunn, M, The US Program for Disposition of Excess Weapons Plutonium, Paper to International Atomic Energy Agency Conference, Vienna, June 1997.

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About the Author 

Charles F Barnaby
Frank Barnaby, a nuclear physicist, worked at the: Atomic Weapons Research Establishment, Aldermaston (1951-57); University College, London

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