Spent Fuel Pool

From What-If folks: What if I took a swim in a typical spent nuclear fuel pool? http://what-if.xkcd.com/29/ ...."Assuming you’re a reasonably good swimmer, you could probably survive treading water anywhere from 10 to 40 hours. At that point, you would black out from fatigue and drown. This is also true for a pool without nuclear fuel in the bottom."