As the Nuclear Security Summit meets in The Hague this week, Japanese Prime Minister Abe and US President Obama have jointly announced that Japan will transfer all plutonium and highly enriched uranium (HEU) from Japan's Fast Critical Assembly (FCA) at Tokai to the US for disposal. This material includes 331kg of weapons grade plutonium and 200kg of weapons grade HEU.

The material was supplied to Japan in the 1960s by the US and UK. The FCA was used in experiments for designing fuel for fast breeder reactors. The US will convert the material to less sensitive forms: the plutonium will be disposed of and the HEU downblended.

This agreement is a major achievement for both nuclear security and non-proliferation. It will remove weapons grade material from a civil site in Japan and bring it under military-standard security in the US while it is disposed of. At the same time, the agreement decisively addresses any suspicions that the material is being retained for a nuclear weapons option. China recently expressed concern about Japan continuing to hold this material, which is sufficient to produce some 60 nuclear weapons.

Japan is to be commended for acting to eliminate this weapons grade material. However, Japan still has significant quantities of weapons grade plutonium contained in 'blanket' assemblies from its fast breeder reactor program. Japan has said this material will be reprocessed in such a way as to dilute the plutonium with lesser quality ('reactor grade') plutonium.

Other countries will take a close interest in how this material is dealt with. A similar issue arises with India, which plans to use fast breeder reactors to produce weapons grade plutonium for use in other reactors. Separation and handling of weapons grade plutonium raises regional tensions and also presents a serious terrorist risk.

Japan will continue to have substantial holdings of reactor grade plutonium from the reprocessing of power reactor fuel. There are some nine tonnes of this material in Japan itself, and a further 35 tonnes held on Japan's account in the UK and France. If the Rokkasho reprocessing plant (pictured), awaiting safety assessment by Japan's Nuclear Regulatory Authority, proceeds, Japan's holdings of separated reactor grade plutonium could increase by six tonnes or more every year.

The International Atomic Energy Agency's plutonium management guidelines set out the principle of balancing supply and demand, by which plutonium stockpiling should be avoided and plutonium separated only at the rate it is consumed. It is understood the draft communiqué for this week's Nuclear Security Summit also calls for minimising stocks of separated plutonium, though apparently this has yet to be agreed by all participants. It is to be hoped Japan will commit to this principle and will urge others to do the same.

The Lowy Institute's research on nuclear issues is supported by a grant from the Nuclear Security Project of the Nuclear Threat Initiative.

Photo courtesy of Wikipedia.