...Like number COVID casualties...
This is in theory.
It is true that Tsar Bomb produced 97% of energy out of fusion but this was just a feature of the test.
Natural uranium tamper is doubling yield of thermonuclear weapon.
Russian test did not include it because its workings were already well understood and 100 Mt weapon would not be survivable to aircraft crew at bomber speeds available and also radiation fallout would not be acceptable on such a large scale even for Soviets.
Nevertheless modern thermonuclear weapons uniformly contain natural uranium tamper which is a cheap and efficient way to double the yield (natural uranium is fissile by fast neutrons produced by fusion).
So about 50% of energy in modern thermonuclear warheads is coming out of fission and they are not as clean as many think (albeit due to high yield most of radioactive by-products are ending up in jet stream, not in immediate fallout 10 or 20 miles next to ground zero.
nuclear reactor use Uranium and produce isotopes at the heavy end of the table , while some are short lived ,
there is some with half live longer than a human life span ,
keeping the spent fuel in a cooling pond for a couple of years see the total radioactivity drop substantially
the residual radiation is best to be left in peace for a couple of decade then reprocessed
Short living fission products are of great concern and long living transuranides like Plutonium-239 are far less radiotoxic than commonly believed.
Number of workers exposed to Plutonium-239 in 1950-thies have been shown to enjoy longer life than average member of public. No cancers either.
Nuclear power both civilian and military is powerful stuff and is no joking matter
but the meme of demonic nuclear is just that , a made up propaganda exaggeration
...unless it goes Fukushima...