The government of Japan released The Status Report of Plutonium Management in Japan - 2017, which details its plutonium holdings. According to the report,
As of the end of 2017, the total amount of separated plutonium both managed within and outside of Japan was approximately 47.3 tons, approximately 10.5 tons of which was held domestically and the rest of approximately 36.7 tons was held abroad.
In 2016, Japan reported having a total of 46.9 tons of separated plutonium, of which 9.8 tons were held domestically.
The changes reflect several developments. First, 0.7 tons of plutonium in MOX fuel was shipped from France to Japan, reducing the amount of plutonium held in France to 15.486 tons (16.217 tons in 2016). According to the report, "reprocessing of spent fuel contracted out to France has been completed." The 0.4 tons increase in the total amount of plutonium reflects the increase of the amount of material held in the United Kingdom from 20.839 to 21.232 tons as separation activities there continue. Japan expects that in 2018-2019 the United Kingdom will complete separation of about 0.6 tons of Japan-own plutonium still contained in spent fuel there.