The government of Japan released The Status Report of Plutonium Management in Japan - 2016, which details its plutonium holdings. According to the report,
As of the end of 2016, the total amount of separated plutonium both managed within and outside of Japan was approximately 46.9 tons, approximately 9.8 tons of which was held domestically and the rest of approximately 37.1 tons was held abroad.
In 2015, Japan reported having a total of 47.9 tons of separated plutonium, of which 10.8 tons were held domestically.
The change of the amount of plutonium held in Japan reflects several developments. First, 904 kg of plutonium taken off the balance is in MOX fuel that was loaded in two power reactors at the Takahama plant that began operations in 2016 - 720 kg in Unit 3 and 184 kg in Unit 4. Second, in March 2016 331 kg of plutonium was removed from the Fast Critical Assembly in JAERI Tokai Research Establishment and shipped to the United States. At the same time, the 2016 report accounts for 251 kg of plutonium that is contained in the fuel of Monju fast neutron reactor that has not been irradiated. This material was not included in previous reports.
The Tokai reprocessing plant is reported to have separated 244 kg of plutonium (compared to 308 kg in 2015). The plant in Rokkasho has not separated any plutonium.
Of the total of 37.1 tons of plutonium held abroad, 16.2 tons are in France and 20.8 tons - in the United Kingdom. According to the report, "reprocessing of spent fuel contracted out to France has been completed." Japan expects that the amount of plutonium held in the United Kingdom will increase by 1 ton by 2018.