One of the bombs dropped on Japan was a plutonium bomb. By design it was intended to convert a maximum amount of the plutonium into destructive energy. Any plutonium remaining after the blast would be wasteful.
From years back I recall reading that the U.S. only had a 30 year supply of uranium for powering reactors. The solution to that problem was to build "breeder" reactors which would not only supply energy but would convert some of the uranium into plutonium which could then be separated out and used to power plutonium reactors. Such a process would then give us a 300 year supply of nuclear energy.
So, we are comparing a nuclear weapon explosion where it was intended to destroy all of the plutonium with spent reactor fuel which may have been intended to create plutonium.
I don't know the extent to which my explanation would apply specifically to Fukishima. I think I read that at least one of the reactors was powered by plutonium. At some point the fuel would be "spent" to the point that the reactor would not be efficient, but that might still leave half or more of the original plutonium in the spent rods.
That is a sound explanation. Thanks.
Canada will sell you all the uranium you need for hundreds of years. If you want it.