Just when you thought it was safe to go back in the water.
What if I took a swim in a typical spent nuclear fuel pool? Would I need to dive to actually experience a fatal amount of radiation? How long could I stay safely at the surface?
Spoiler alert, but necessary for my comment
In fact, as long as you were underwater, you would be shielded from most of that normal background dose. You may actually receive a lower dose of radiation treading water in a spent fuel pool than walking around on the street.
This jibes with my experience in the navy — the crew had their exposure monitored, and the word was that it wasn’t unusual for someone on a sub not directly being exposed to radioactive/contaminated materials or hanging out near the reactor compartment to have their dose be lower than what one would get on the surface. The benefitted from spending most of their time several tens of meters blow the surface, and all of the attenuation that afforded.