On Oct 9, the China Arms Control and Disarmament Association and the China Institute of Nuclear Information and Economics jointly published the Study on Japan's Nuclear Materials. The study, citing data issued by the Japanese government in August 2015, says “Japan has 47.8 tons of highly sensitive separated plutonium, 10.8 tons of which are stored in Japan.” In addition, Japan also has about 1.2 tons of highly enriched uranium.
It is known to all that nuclear energy technology could be applied in both military and civilian uses, and highly enriched uranium and plutonium are all “direct-use materials” for producing nuclear weapons. On Aug 6 and 9, 1945, the two atomic bombs dropped by US fighters in Hiroshima and Nagasaki were a uranium atomic bomb and a plutonium atomic bomb, respectively.
Since the late 1950s, however, Japan has been developing its nuclear energy industry with “dual purposes” -- nuclear power reactors for commercial use and its capabilities in nuclear weapons through the accumulation of nuclear-fuel recycling technologies. Political figures in Japan have repeatedly made dangerous comments on “possessing nuclear weapons,” including Nobusuke Kishi, the maternal grandfather of Shinzo Abe, who said in a letter to the US government in 1957 that from a defense perspective, Japan “believed it was essential that Japan have a nuclear arsenal”; the Japanese government headed by Prime Minister Eisaku Sato, another maternal grandfather of Shinzo Abe, which discussed in the late 1960s the possibility of possessing nuclear weapons in a “highly secret” way and submitted a study report; and Shinzo Abe himself, who said in 2002 that the country's “constitution does not preclude the acquisition of nuclear weapons for tactical defense.” Furthermore, plutonium is a highly toxic and dangerous substance and must be strictly controlled in order to prevent it from falling in the hands of terrorists. For instance, principal members of the Aum Shinrikyo cult, which planned and carried out the sarin gas attack in Tokyo's subway system in 1995, once attempted to seize nuclear materials. With all these factors in consideration, people have reason to demand that Japan show an honest and responsible attitude, and to take action to dispel concerns of the international community about its nuclear intentions.
It is worth mentioning that as early as in November 1955 when Japan and the United States signed the atomic energy agreement, the United States agreed to provide 6 kilograms of uranium-235, a nuclear material with enrichment as high as 20%. In an attempt to achieve the “localization” of highly enriched uranium, Japan set up the Japan Atomic Energy Research Institute in Tokai in June 1956 to serve as the custodian site for the loaned highly-enriched uranium and relevant researches. From the late 1960s to the mid-1970s, Japan started the construction of a highly enriched uranium plant in Ningyo-Toge, and the construction got into full swing in March 1982. The commercial highly enriched uranium processing plant, founded by Japan Nuclear Fuel Limited in Rokkasho-mura, was completed and put into operation in March 1992. It is obvious that long term support by the United States is the reason Japan could have possessed about 1.2 tons of highly-enriched uranium.
In terms of plutonium material, it's something like burning coal to heat boilers, as there would always be coal not fully burned in the slags. When light-water reactors “burn” low-grade uranium, the used nuclear fuels, known as spent fuels, contain some “useful substances” (about 1% of plutonium and 1% of uranium-235) due to insufficient reaction. Experts have estimated that if Japan treats and reprocesses spent fuel from its nuclear power plants and recycles the separated plutonium, it could help reduce about 25% of the country's natural uranium imports. For Japan, which has to rely on imports for uranium, it would be a considerable resource and would be regrettable if disposed of. However, because it has not been capable of treating and processing the spent fuel, Japan has had to ship its spent nuclear fuels to Europe, commissioning the treatment and reprocessing tasks to British and French companies, and then shipping the separated plutonium back to Japan. Beginning from 1978, Japan shipped hundreds of tons of spent nuclear fuel to Britain and France each year. In the late 1990s when the amount was huge, Japan had to use jumbo passenger jets like the Boeing 747 every half month to transport plutonium back to Japan from France and Britain, and the amount of each shipment was about 250 kilograms. Due to the distance between Japan and the countries providing treatment and reprocessing services, whenever Japan was transporting back the processed plutonium, by air or sea, it always caused concerns and opposition from the passing countries. This forced Japan to make a decision to construct its own treatment and reprocessing plant.
After Jimmy Carter was sworn in as the president in January 1977, and the Nuclear Non-Proliferation Act was announced, the United States decided to postpone indefinitely its plan for the construction of commercial treatment and reprocessing plant, and asked its allies to follow the rules accordingly. For Japan, in particular, it required Japan to get consent from the United States before it could put the Tokai reprocessing plant, which was then near completion, into operation. After three rounds of talks on used nuclear fuel reprocessing from April to September in 1977, however, the United States made concessions, and agreed to let Japan to conditionally put the Tokai reprocessing plant into operation. Although conditions were attached, it provided Japan an opportunity to separate and enrich plutonium materials. In the 1970s, the United States also required Japan to get US approval for each shipment of plutonium from Britain and France. After Ronald Reagan became the president in 1981, the United States relaxed its requirements on Japan for plutonium shipments from Europe, from approval for each shipment to approval for shipment when some conditions were met. This is another reason for the growing accumulation of plutonium in Japan. Additionally, the United States once provided 330 kilograms of weapon-grade plutonium and 30 kilograms of uranium to Japan for “research” purposes.
With these factors taken into account, it should be pointed out that the United States must assume its special responsibility for the fact that Japan has a growing inventory of nuclear materials. With technological progress rising and technical requirements for plutonium enrichment getting lower, it is no longer impossible to make nuclear weapons through plutonium enrichment. Therefore, the International Atomic Energy Agency has placed plutonium, either weapons-grade or reactor-grade, on the “Safeguards Glossary”. For this reason, the United States must strengthen its supervision over Japan's attraction to nuclear weapon possession.
