On the worst-case scenario at Fukushima …
If all the plutonium in Fukushima explode and disperse in the atmosphere, according to the most conservative estimates, the number of deaths of approximately 920 million people.
Most cited results from Ralph Nader said that pound of plutonium dust dispersed in the atmosphere would be enough to kill 8 billion people. However, the math shows that one pound of plutonium could kill up to 2 million people. Thus, the toxicity of plutonium can be compared with nerve gas.
However, this most plutonium in Fukushima damn much!
According to TEPCO, the Fukushima reactors 1-3 stored 210 kg of plutonium.
It is somewhere around 460 pounds, and even if we decide on a minimum — two million deaths per 1 pound, the 460 x 2 million = 920 million.