Japan’s Separated Plutonium Inventory (as of end of 2016)
On August 1 2017, Japan’s Nuclear Safety Commission released data on plutonium storage conditions as of the end of 2016. The International Atomic Energy Agency (IAEA) revised its evaluation methods for unirradiated plutonium in September 2016, bringing to light 251 kg of unirradiated plutonium that had been loaded into the Monju reactor. Specifically, the evaluation method was revised to include unirradiated plutonium loaded into nuclear reactors in addition to other plutonium accounted for previously, with the objective of making the assessment of civil unirradiated plutonium holdings clearer under the IAEA’s International Plutonium Management Guidelines. After the criticality test operation of Monju in May 2010, the fuel was exchanged. It has remained there to this day with no operations resuming (and the decision made to decommission the reactor), so the unirradiated amount inside the reactor will now be accounted for.
Also, 331 kg of plutonium that was part of a 444 kg criticality test apparatus was transferred to the Savannah River National Laboratory in March 2016, so the amount has decreased.
The total amount of plutonium in Japan has decreased by about one ton due to irradiation of MOX fuel starting with the resumption of operations at Takahama Units 3 and 4. This can be determined from differences in amounts held in commercial nuclear power reactors.