Comment by Retric
2 months ago
> Here's what I got: the radiation level just 1 meter away from the "elephant foot" (the solidified molten core), at the time of the accident was about 1000 times lower than the solar irradiation. At 100 meters it was 10 million times lower (because of the inverse square law).
No, the elephants foot isn’t a point source at its surface.
To use an extreme example going from 1m away from the sun to 100m away from the sun doesn’t result in a 10,000x drop off in energy density. Instead the exponential drop-off occurs relative to the center of the sun because energy is coming from any point on the surface visible to that location. A similar principle applies with the elephants foot, though the geometry is more complicated.
I treated the elephant foot as a point source. It’s a back of the envelope calculation. Maybe I’m off by a factor of 10, but I’m not off by a factor of one million.
I mean if your benchmark was “at the time of the accident” then you’re off by more than a factor of a million. The often quoted 80 to 100 grays per hour was eight months after formation and it had gotten way less radioactive by then. Decay heat which all comes from radioactivity was ~1% of full reactor output for a few days. ~10,000 kW or so from a fairly compact object which is why it was still melting through concrete.
As to a point source, if you’re making an approximation use the center of the object and your 100m distance calculation would be corrected by about 25x. Though obviously the building itself provides shielding.
I used the figure you quoted, which I got from wikipedia [1]. I said "at the time of the accident"; you are pointing out it was 8 months after the accident. I guess I should specify all the details in my comments on HN going forward? I said that now the radiation level must be lower, and I could't find any more recent estimates, but I ballparked it at 100x lower.
In the end, I'm not sure what your point is? Are you disagreeing with my overall estimate that the energy produced by the elephant's foot's radioactivity at 100 meters distance is one billion times lower than the energy we receive from the sun, and therefore fungi can't "feed" on it, because this energy is nowhere near enough to sustain life?
[1]https://en.wikipedia.org/wiki/Elephant%27s_Foot_(Chernobyl)#...
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