I have to call bullshit again and again.
First, you literally wrote ”plutonium fire that wipes out all human life in the northern hemisphere. Feel free to take it back, but do not pretend you didn’t say it. This is exactly what you said.
Second, nuclear fuel uses uranium oxide as a fissile material. Sometimes plutonium oxide added to it, and some plutonium is produced from uranium oxide during the work cycle. Again, do not hesitate to prove me wrong, but all plutonium in the fuel is already oxidized and unlikely to catch fire.
Third, get your numbers consistent, and if at all possible, get them right too. Was it ”1400 spent fuel rods”? Or was it ”4000 tons initially, 1400 tons now of spent fuel”? One rod doesn't weigh one metric ton, it is about the size and weight of the metal stick. The link you provided says there were 566 _assemblies_, which is ~140 tons assuming 250 kilos per assembly. Wikipedia says there were 854 tons of fuel in all 4 reactors and spent fuel pools combined, 104 of them in the unit 3 pool. I wonder if this is pure fuel weight or gross weight.
Forth, a few micrograms of plutonium is not a fatal dose. It is associated with an increased risk of cancer, which is not a definition of ”fatal”, or LD50, or anything like this.
And fifth, plutonium only makes ~1% of the fuel. fix your math, please.
Would you mind reposting your claim, only using correct amounts of materials, working chemistry and your actual idea of the consequences to the human race? Something more specific than jumping from total annihilation to vague ”it has potential”.