In the fall of 1940, the Japanese army concluded that constructing an atomic bomb was indeed feasible. The Institute of Physical and Chemical Research, or Rikken, was assigned the project under the direction of Yoshio Nishina. The Japanese Navy was also diligently working to create its own "superbomb" under a project that was dubbed F-Go, headed by Bunsaku Arakatsu at the end of World War II. The F-Go program (or No. F, for fission) began at Kyoto in 1942. However, the military commitment wasn't backed with adequate resources, and the Japanese effort to an atomic bomb had made little progress by the end of the war.
Japan's nuclear efforts were disrupted in April 1945 when a B-29 raid damaged Nishina's thermal diffusion separation apparatus. Some reports claim the Japanese subsequently moved their atomic operations Konan (Hungnam, now part of North Korea). The Japanese may have used this facility for making small quantities of heavy water. The Japanese plant was captured by Soviet troops at war's end, and some reports claim that the output of the Hungnam plant was collected every other month by Soviet submarines.
There are indications that Japan had a more sizable program than is commonly understood, and that there was close cooperation among the Axis powers, including a secretive exchange of war materiel. The German submarine U-234, which surrendered to US forces in May 1945, was found to be carrying 560 kilograms of Uranium oxide destined for Japan's own atomic program. The oxide contained about 3.5 kilograms of the isotope U-235, which would have been about a fifth of the total U-235 needed to make one bomb. After Japan surrendered on August 15, 1945, the occupying US Army found five Japanese cyclotrons, which could be used to separate fissionable material from ordinary uranium. The Americans smashed the cyclotrons and dumped them into Tokyo Harbor.Although possession of nuclear weapons is not forbidden in the constitution, Japan, as the only nation to experience the devastation of atomic attack, expressed its abhorrence of nuclear arms early on and determined never to acquire them. The Basic Atomic Energy Law of 1956 limits research, development, and utilization of nuclear power to peaceful uses, and beginning in 1956, national policy has embodied "three non-nuclear principles"--forbidding the nation to possess or manufacture nuclear weapons or to allow them to be introduced into the nation. Prime Minister Eisaku Sato made this pledge - known as the Three Non-Nuclear Principles - on February 5, 1968. The notion was formalized by the Japanese Diet on November 24, 1971. In 1976 Japan ratified the Nuclear Non-Prolifeation Treaty (NPT), adopted by the United Nations Security Council in 1968, and reiterated its intention never to "develop, use, or allow the transportation of nuclear weapons through its territory." Japan became a signatory to the Comprehensive Nuclear-Test-Ban Treaty in 1997 and has membership in many non-proliferation efforts, including the Nuclear Suppliers Group (NSG), Missile Technology Control Regime (MTCR), and the Zangger Committee.
Japan lacks significant domestic sources of energy except coal and must import substantial amounts of crude oil, natural gas, and other energy resources, including uranium. Japan's nuclear output nearly doubled between 1985 and 1996, as Japan attempted to move away from dependence on oil following the 1973 Arab oil embargo. The Japanese government is committed to nuclear power development, but several accidents in recent years have aroused public concern. During the past few years, public opposition to Japan's nuclear power program has increased in reaction to a series of accidents at Japanese nuclear plants, including a March 1997 fire and explosion at the Tokai-mura reprocessing plant. Other problems for Japan's nuclear power program have included rising costs of nuclear reactors and fuel, the huge investments necessary for fuel enrichment and reprocessing plants, several reactor failures, and the question of nuclear waste disposal. Regardless, Japan plans to increase the proportion of electricity generated from nuclear to 40% by 2017 and 50% by 2030. As of 2000, Japan ranked third worldwide in installed nuclear capacity, behind the United States and France.
Japan’s nuclear power development suffered a crippling blow on March 11, 2011 after the Tōhoku earthquake and tsunami caused three of the six nuclear reactors at the Fukushima I Nuclear Power Plant to meltdown. The Fukushima Daiichi nuclear disaster was the largest nuclear disaster since Chenobryl in 1986. As of March 2012, only two of Japan’s 54 nuclear reactors were still operating, due to safety concerns regarding nuclear power. Trade Minister Yukio Edano was quoted by Reuters saying that “it is quite possible that no reactors will resume operations towards the summer.” With the Japanese public and Japanese officials no longer as confident regarding nuclear power, Japan has been importing more oil and liquefied gas for power.
To enhance its energy security, the government advocates uranium and plutonium recovery through reprocessing of spent fuel. The Power Reactor and Nuclear Fuel Development Corporation (PNC) operates a reprocessing plant with an annual capacity of 90 tons but a larger reprocessing plant, Rokkasho-Mura, with a capacity of 800 tons per year, originally planned for 2003, isthe first reprocessing plant in an NPT non-nuclear weapon state. Reprocessing is expensive and costs can quickly rise with new safety requirements and the development of new technologies. Estimated in 1993 to cost about $8 billion, a more recent estimate for Rokkasho-Mura places the total at $15 billion. Japan also is interested in recycling recovered plutonium. In 1999, Japan began, in two prefectures, a controversial mixed-oxide utilization plan, which involves burning a highly toxic mix of plutonium and uranium on a commercial scale.
The reprocessing plant at Tokai in Ibaragi has been reprocessing spent fuel since 1981, though its operation was temporarily halted by a fire and explosion in March 1997. A commercial-size reprocessing plant has been under construction since 1993 at Rokkasho in Aomori prefecture. The Recycle Equipment Test Facility (RETF) is designed to reprocess plutonium produced in Monju and Joyo, Japan's two fast breeder reactors. Approval for construction was given by the Science and Technology Agency and announced on December 13, 1994. Japan Nuclear Fuel Ltd. (JNFL) has announced that initial operation of the reprocessing plant currently being constructed in Rokkasho-Mura, Aomori Prefecture has been delayed to October 2012 due to complications during testing. This most recent postponement is the 18th delay in launching initial operations at Rokkasho-Mura. The previous plan called for operations to begin in January 2003. With a large store of plutonium, Japan mainly relies on Britain and France to recover plutonium from nuclear waste. Weapon-grade plutonium is nearly pure plutonium 239, whereas the plutonium in commercial fuel is much lower in plutonium 239 and higher in the isotopes that are undesirable for weapons use. This, however, is not a crucial difference, since all plutonium can be used in weapons. The US nuclear weapons arsenal does not utilize commercial (reactor grade) plutonium from spent fuel. Tests were completed, however, to confirm that reactor grade plutonium could be used in a nuclear explosive and is therefore a nonproliferation concern.Tokyo pledged in 1991 that it would adhere to the principle of not retaining surplus plutonium. Since 1994 the Japanese Atomic Energy Commission (JAEC) has published annual inventories of separated plutonium. As of December 1995, the total inventory of separated plutonium managed by Japan was 16.1 tons, with 4.7 tons in Japan and 11.4 tons in Europe. A nuclear bomb similar to the one exploded in Nagasaki can be made with seven to eight kg of plutonium.
Japan's small size, its geographically concentrated industry, and the close proximity of potentially hostile powers all render the country vulnerable to a nuclear strike. North Korea's attempts to develop nuclear weapons coupled with its capability to target Japan with any weapon that it developed, is a matter of great concern to Japanese military strategists. Events on the Asian mainland could also affect Japan. Since the early 1970s, China has possessed a nuclear force capable of striking Japan.
Having renounced war, the possession of war potential, the right of belligerency, and the possession of nuclear weaponry, it held the view that it should possess only the minimum defense necessary to face external threats. The Japanese government values its close relations with the United States, and it remains dependent on the United States nuclear umbrella.
During the Sato cabinet in the 1960's, it is reported that Japan secretly studied the development of nuclear weapons. On June 17, 1974, Japanese Prime Minister Tsutomu Hata told reporters that "it's certainly the case that Japan has the capability to possess nuclear weapons but has not made them." This remark aroused widespread concern in the international media at that time. Japan's nuclear power program based on reprocessed plutonium has aroused widespread suspicion that Japan is secretly planning to develop nuclear weapons. Japan's nuclear technology and ambiguous nuclear inclinations have provided a considerable nuclear potential, becoming a "paranuclear state." Japan would not have material or technological difficulties in making nuclear weapons. Japan has the raw materials, technology, and capital for developing nuclear weapons. Japan could possibly produce functional nuclear weapons in as little as a year's time. On the strength of its nuclear industry, and its stockpile of weapons-useable plutonium, Japan in some respects considers itself, and is treated by others as, as a virtual nuclear weapons state. The Japanese people’s abhorrence of nuclear weapons and newfound distrust of nuclear power since 2011 and Japan’s involvement in non-proliferation efforts make the possibility of Japan acquiring nuclear weapons unlikely.