What what I can tell they use "dropped" to refer to just falling to the bottom of their shaft, though it definitely does evoke the idea of them just rattling around down there in my head. I think that since water is such a good buffer, that once you turned off the pressure you could open a hatch and just kind of fish out whatever you wanted with a very long pair of tongs. This is obviously a research sized reactor, but you can see they're happily mucking about with it on the other end of long poles, and the scientist says they could hypothetically fish something back out: https://youtu.be/5QcN3KDexcU?t=329