This post contains a summary of INFCIRC/549 reports by the countries that submit annual civilian plutonium declarations that reflect the status of civilian plutonium stocks as of 31 December 2016.
Japan (INFCIRC/549/Add.1-20) reported having 9.9 tons of plutonium in the country and 37.1 tonnes abroad (the 2015 numbers were 10.7 and 37.1 tons respectively). In August 2017 Japan also released a more detailed internal version of this report, "The Status of Plutonium Management in Japan".
Germany (INFCIRC/549/Add.2-20) reported 0.5 tons of separated plutonium in the country (1.8 tons in 2015). Germany does not report separated plutonium outside of the country. It is believed to be about 2-3 tons.
Belgium (INFCIRC/549/Add.3-16) declared no separated plutonium in storage or at reprocessing plants and "less than 50 kg" of separated plutonium in all other categories. It is likely that all material belongs to foreign bodies (900 kg was reported in this category in 2014). [UPDATE: In its 2017 report, Belgium corrected that number - no foreign plutonium was in the country as of 31 December 2016.]
Switzerland (INFCIRC/549/Add.4-21) declared "less than 2 kg" of separated plutonium "held elsewhere" (it was "less than 50 kg" in 2015). This reflects the removal of 18 kg of plutonium to the United States.
France (INFCIRC/549/Add.5-21) reported having 81.7 tons of separated unirradiated plutonium in its custody. Of this amount, 16.3 tons belongs to foreign countries. Almost all that plutonium - 16,217 kg - belongs to Japan. The amount of plutonium owned by France is 65.4 tons. The numbers indicate that France separated 2 tons of plutonium in 2016.
The United States (INFCIRC/549/Add.6-20) declared 49.4 tons of separated plutonium, of which 4.6 tons are in MOX fuel and 44.8 tons are "held elsewhere" (most of this material is believed to be in weapon components). This is an increase of 0.4 tons compared to the 2015 declaration. The document explains that the additional material was "accepted by the United States from other nations under nuclear nonproliferation programs." This should include the 331 kg of plutonium removed from Japan as well as the material removed from Germany and Switzerland (believed to be 30 kg and 18 kg respectively).
China (INFCIRC/549/Add.7-16) declared having 40.9 kg of separated plutonium, an increase from 25.4 kg reported in 2015.
The United Kingdom submitted its 2016 report, INFCIRC/549/Add.7-16, in February 2018. The report contains the information that has been posted on the Office for Nuclear regulation website. As of December 2016, the United Kingdom had the total of 133.5 tons of separated plutonium in the country, of which 23.2 tons belonged to foreign bodies (including 20.839 tons of Japan's plutonium).
Russia (INFCIRC/549/Add.9-19) reported 57.2 tons of civilian plutonium. This includes 54.9 tons of material in storage, 1.7 tons of plutonium in unirradiated MOX and 0.6 tons of plutonium stored elsewhere. The numbers in 2015 were 53.1, 1.5, and 0.8 tons respectively for the total of 55.4 tons.
In addition to reporting plutonium stocks, some countries also submit data on their civilian HEU:
Germany reported 0.33 tonnes of HEU in research reactor fuel, 0.94 tonnes of HEU in irradiated research reactor fuel, and 0.01 tonnes in the category "HEU held elsewhere." It's a slight increase from the 2015 numbers - 0.3, 0.93, and 0.03 tons respectively.
France declared 4806 kg of HEU (4598 kg in 2015), of which 3004 kg is unirradiated material - 1028 kg of HEU at fuel fabrication or reprocessing plants, 111 kg at civil reactor sites, 2125 kg at various research facilities. Also declared are 1593 kg of irradiated HEU - 147 kg at civil reactor sites and 1394 kg in other locations. The increase of 247 kg of HEU at fuel fabrication plants probably reflects the HEU held by Areva, which manufactures fuel for the German FRM-II reactor. This material is being supplied by Russia.
The United Kingdom reported having 1,370 kg of HEU (1.404 kg in 2015). Of this amount, 1,233 kg is unirradiated HEU: 2 kg of unirradiated HEU is stored at the enrichment plants, 372 kg - at fuel fabrication facilities, and 858 kg - at other sites. Irradiated HEU is located at civil reactor sites (5 kg) and other sites (132 kg).