What would happen if you went swimming in a spent fuel pool?

If one of my modern-day characters, a nuclear power-plant worker decides to take a swim in one of these pools, what will happen?

Would he die, get sick, or not much?

• Solved by XKCD what-if.xkcd.com/29 It's the first result on google when searching your question title. – Trevor Jan 31 at 17:11
• I personally feel that even though xkcd has addressed this, it's still worth answering this question. The answer given there, while awesome, is largely of non-quantitative and only talks about one specific incident. There's more data out there to use. (For what it's worth, I've tried to do this in my answer, but I'm still sure there's even more information out there that could be useful.) – HDE 226868 Jan 31 at 17:47
• @HDE226868 Seems pretty broad to me. What will happen? Anything could happen. And question shows no research effort prior to asking – Trevor Jan 31 at 17:51
• Don't forget XKCD's ultimate answer to the question: "The security guards will shoot you as you try to get into the pool....." – Thucydides Jan 31 at 23:15
• @TrevorD I could agree with you about not enough research effort, but not sure I see the too broad aspect. Either the diver will get sick (and maybe die), or not, and using a typical pool, we can figure that out for most reasonable scenarios. – HDE 226868 Feb 1 at 17:52

$$\begin{array}{|c|c|c|c|}\hline \text{Energy (keV)} & \text{Half-value layer (cm)}\\\hline 100 & 4.15\\\hline 200 & 5.1\\\hline 500 & 7.15\\\hline \end{array}$$ At the surface, the fractional intensity is tiny.