Japan's new policy on its plutonium stockpile

Tatsujiro Suzuki and Masa Takubo

On 31 July 2018, Japan's Atomic Energy Commission (JAEC) issued a new policy paper, The Basic Principles on Japan's Utilization of Plutonium, which for the first time, stated that "Japan will reduce the size of its plutonium stockpile." A similar statement was included in the new Strategic Energy Plan (in Japanese) by the Ministry of Economy, Trade and Industry (METI) that was adopted on 3 July by the Cabinet of the Japanese government.

Japan's plutonium stockpile, according to the data released by the JAEC at the same time as the new policy, is about 47.3 tons of plutonium (as of the end of 2017), of which 36.7 tons is overseas (21.2 tons in UK and 15.5 tons in France) and 10.5 tons in Japan. The Rokkasho reprocessing plant, with a design separation capacity of 8 tons of plutonium per year, on which stated construction in 1993, is currently planned to be completed in 2021. Plans call for the J-MOX plant to be completed in 2022 to turn this plutonium into MOX fuel for light water (LWR) nuclear power reactors.

Summary of JAEC's new policy

The new policy has five key aspects.

Reprocessing will be approved by METI under the Spent Nuclear Fuel Reprocessing Implementation Act only to the extent necessary for specified MOX use in LWRs. The government will assure that MOX fuel is to be fully consumed in a timely manner by instructing the operators.

Reactor operators are to "minimize the [unirradiated plutonium-containing] feedstock" between reprocessing and irradiation.

The utilities are to focus on reducing Japan's plutonium stockpile stored overseas through measures including "collaboration and cooperation," i.e. transfer of ownership to reactor operators in a position to use more unirradiated plutonium than they own.

Japan's Atomic Energy Agency must examine all options including disposal of the unirradiated plutonium it acquired for R&D purposes if there is no concrete plan to use.

Spent fuel storage capacity is to be expanded steadily.


The new policy is a step into a right direction. It is not sufficient, however, to guarantee that there will in fact be a "reduction" of Japan's plutonium stockpile. There are several reasons for this.

The new policy is based on the assumption that the Rokkasho reprocessing plant will be operated. Unless the government changes this policy, it will be difficult to reduce Japan's plutonium stockpile substantially.

If the Rokkasho reprocessing plant is started as scheduled, it will be difficult to realize the new policy that Japan's total "stockpile will not increase from the current level." Certainly, the stock of unirradiated plutonium in Japan is likely to increase greatly as long as the necessary minimum MOX feed stock and use plans remain undefined,

Although the pace of plutonium separation at Rokkasho can be controlled by METI, the government has no legal authority to control the rate of plutonium use in MOX to assure that plutonium use exceeds plutonium supply. JAEC's new policy does not have any specific plan to remedy this lack of authority.

Minimizing the "feedstock" is the right policy but will have no significant impact on the utilities' reprocessing plans in the absence of a clear specification of what is expected to be the acceptable "minimum" stock of unirradiated plutonium.

The plan to have the J-MOX fuel fabrication plant start one year after the startup of the Rokkasho reprocessing plant may be as wildly optimistic as was the original plan to start commercial reprocessing at Rokkasho in 1997.

The new policy focuses on MOX use of plutonium stored in France and the UK and suggests that ownership of plutonium there should be transferred among utilities so that those that have operating reactors licensed to use MOX can consume plutonium owned by others who don't. Transfer of ownership of plutonium among utilities has been done before. If necessary, the government can exercise its legal authority under Article 13 of Japan's Atomic Energy Basic Act which allows the government to order institutions to transfer fissile materials with specified price.

It will take some ten years to use as MOX fuel in Japanese reactors the Japanese plutonium stored in France, even assuming the free transfer among Japan's utilities of this plutonium. Japan has only four operating reactors licensed to use MOX with a combined capacity to consume about two tons of plutonium per year without much hope for more MOX-using reactors to come on line in the next several years. About two tons of plutonium in MOX is already in the pools of those reactors waiting to be loaded.

Japan owns almost all of the remaining foreign plutonium stored in UK. The UK does not have a MOX fuel fabrication plant, however. The new policy did not discuss the proposal made by the UK Nuclear Decommissioning Authority to take over title of foreign-owned plutonium stored in UK. As of January 2017, the UK had taken title to 8.5 tons of foreign plutonium it has separated and stores. Transfer to the UK of title to the remaining Japanese plutonium should be considered a "win-win" deal for both Japan and the UK. It also would reduce the challenge of securely transporting plutonium from Europe to Japan.

JAEC's mention of "disposal" of R&D plutonium is the first time that the government has described Japan's stock of separated plutonium as a "disposal" problem rather than as a "resource". This is a hopeful sign.

Encouraging spent fuel storage is the right policy but it should be done as an alternative to reprocessing not to facilitate the regulation of the rate of reprocessing.