The Rokkasho used fuel reprocessing plant in Aomori Prefecture

Japan has been adjusting its plans for reprocessing used fuel and producing mixed oxide (MOX) fuel, known as its pluthermal policy, in order to reduce its growing stockpile of plutonium separated from used fuel. This stockpile has been a subject of public and international concern.

In February 2024, the Japan Atomic Energy Commission (JAEC) reiterated Japan's principle of not possessing plutonium without specific purposes and declared a policy to reduce the amount of its plutonium stockpile. However, this reduction is contingent on the operation of the reprocessing plant and MOX plant under construction at Rokkasho in Aomori Prefecture.

Construction of the Rokkasho Reprocessing Plant (RRP) began in 1993 with a planned completion date of 1997, but has faced repeated delays. Similarly, construction of the MOX plant began in 2010 and is now expected to be completed during fiscal years 2026 and 2027.

Currently, only four of Japan's operating nuclear units use MOX fuel. Japan's plutonium stockpile is expected to total around 44.5 tonnes in FY2026, with most of it stored abroad in France and the UK.

The Federation of Electric Power Companies (FEPC) has reaffirmed its plutonium utilisation plan, subject to the operation of the Rokkasho reprocessing plant and MOX fuel plant. FEPC aims for early and maximum implementation of MOX use by at least 2030, with 12 nuclear units using MOX by then.

To establish reprocessing technology for used MOX fuel, FEPC has decided to proceed with a reprocessing demonstration study on spent MOX fuel in France, in collaboration with France's Orano. The study will look at the properties of used MOX fuel and its impact on reprocessing equipment, and demonstrate that MOX fuel used at domestic nuclear power plants can be reprocessed in commercial plants.

Due to delays in the completion of the Rokkasho facility, Kansai Electric has been urged by Fukui Prefecture to address shrinking storage capacity for used fuel. Kansai Electric has drawn up a new road map assuming that the Rokkasho plant will start reprocessing in FY2027 and receiving used fuels in FY2028. The company plans to transport 198 tonnes of used fuel to Rokkasho over three years to FY2030, and 100 tonnes to Orano starting in FY2030.

Overall, Japan is continuing to grapple with the challenge of managing its plutonium stockpile while also pursuing its nuclear energy goals.