Have you ever noticed that if you place a dry piece of paper on a wet table, the paper becomes wet? This happens because a more concentrated medium tends to transfer the substance present in it to a less concentrated medium.
This process of transmission from a more concentrated medium to a less concentrated one is called osmosis.
And you've probably also noticed that there's a maximum amount of sugar you can put into juice, and if you exceed it, the sugar settles at the bottom of the glass. This happens because the medium becomes saturated with sugar and can't dissolve any more.
Now for the answer,
The generators of Nuclear Power Plants are full of radioactive Iodine, the so-called Iodine 131. When this product is released into the atmosphere (examples include the accidents in Chernobyl (1983) and Fukushima (2011)), the main medical action is to give the population Iodine capsules (non-radioactive) so that these people become saturated with Iodine and do not absorb radioactive Iodine from the atmosphere.
It's worth remembering that *potassium iodide* KI is added to table salt to prevent goiter, but the recommended daily dose of iodine is 150 micrograms for people over 14 years old and 220 micrograms for pregnant women. In cases of radioactive accidents, the doses aim to saturate the body, especially the thyroid gland.
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