Thanks for the link, but I think that we can safely assume that if your going to find Plutonium in substantially high contamination doses then there are a few places in the world to look, such as Palomares in Spain and in Thule in Greenland and just north of Las Vegas etc not forgetting the widespread contamination in the old Soviet client states. As the earlier fission bombs weren't particularly efficient then I think you can safely assume that the highest proportion of Plutonium fallout found on the Japanese mainland would be from the Nagasaki detonation using a Plutonium weapon. The later larger more powerful weapons tested in the Pacific were primarily fusion weapons which left very little Plutonium behind. These weapons were also much much further away from the Fukushima site compared to Nagasaki.

Of course the idea that the levels of Plutonium contamination of the Fukushima site by the IAEA could not be distinguished between the level of Plutonium fallout from the use of above ground testing from the 1940s to 1960s and from the fuel from a smoldering No3 reactor using 7% Plutonium Oxide MOX fuel which had ejected the top of the inner pressure vessel containment, which surrounds the inner fuel core, 1500 feet into the air to land on the nearby turbine hall to then have vast qualities of Plutonium contaminated hot particles rain down, is the b*lls*it statement.


Edit - The British did drop the largest ever fission bomb in the Pacific, which dwarfed all other previous fission weapons so this weapon may have produced vast quantities of Plutonium fallout.