Your numbers, as far as they go, look to be in the right ballpark.
I still argue that the amount introduced to the larger environment is much lower than from the above ground tests.
The explosions at Fukishima were chemical explosions, mostly hydrogen gas burning to water. They simply weren't hot enough to vaporize any significant amounts of the metals and concrete in the reactor.
By contrast the nuclear explosions happen at such very high temperatures they directly vaporized anything within hundreds of yards, then heavily irradiated that vapor rendering it highly radioactive and and spreading it far and wide. To get an approximate idea of the mass involved, lets assume the average fire ball was 600 meters in diameter (a W-88 at 350kt yield), and it was on rock and soil. That gives a fireball volume of about 375,000 m3. Let's say half the fireball was "wasted" on the air, i.e. a surface blast. That gives a vaporized crater volume of about 185,000m3. Let's further say that the bomb is only about 55% efficient at vaporizing rock, and further de-rate the initial volume vaporized down to 100,000 m3, just for easy math...
Picking an average rock density of 2.5 g/cm3 gives us 2,500,000 g/m3 or 2500 kg or 2.5 metric tons/m3
Times 100,000m3 gives us 250,000 tons of intensely radioactive fallout per blast. Roughly 450 blasts before the test ban treaty in 1962 gives us a billion tons or so.
That's not counting anything sucked in from the surrounding countryside, nor any seawater pouring into the craters, nor any gasses "vented" from numerous underground tests.
That sounds like a lot.
It IS a lot, but we're still here, aren't we?
You note we are still here - those who died off are indeed not present.
The first time I encountered comparisons between Nagasaki/Hiroshima and Fukukshima, it was in a point for point comparison between the radiation remaining on site after time elapsed. Much more radiation over a larger area is currently present at Fukushima at this point in time compared with nuclear blasts. Some went into the atmosphere to contribute to harmful radiation exposure world wide. But Fukushima has been contributing to atmospheric, land and water contamination freely for over two years now - compare that with the total duration of atomic blasts. Fukushima is worse, unfortunately. Based on medical evidence (e.g., BEIR VII and other studies), we can assume that the overall cancer rate has increased by some degree as a result of loading radioactive contaminates into the atmosphere, land and water.
The explosions at Fukishima were chemical explosions, mostly hydrogen gas burning to water. They simply weren't hot enough to vaporize any significant amounts of the metals and concrete in the reactor. There are some conflicting opinions about how those explosions came about. Did they occur before or after meltout ? Was the explosion a result of meltout or simply overheating ? We know they were venting containment multiple times before the explosions. Some evidence points to steam explosions when the corium hit the sandstone layer below.
Nuclear explosions contain a large portion of light and heat energy. That thermal and blast energy is not radioactive and is what vaporizes the surrounding material. About 15 % of the energy is Nuclear Radiation. Since E=MC2, about 85 % of the mass is converted to thermal and blast energy.
Excerpted from The Energy from a Nuclear Weapon
The remaining 15 percent of the energy is released as various type of nuclear radiation. Of this, 5 percent constitutes the initial nuclear radiation, defined as that produced within a minute or so of the explosion, are mostly gamma rays and neutrons. The final 10 percent of the total fission energy represents that of the residual (or delayed) nuclear radiation, which is emitted over a period of time. This is largely due to the radioactivity of the fission products present in the weapon residues, or debris, and fallout after the explosion.
It IS a lot, but we're still here, aren't we?
Not for much longer my friend.