The duties of a mech eng at a nuclear plant are quite varied, but generally it is solving small problems (like a valve manufacturer has changed the part numbers for a bonnet seal, someone has to confirm that the parts with e new numbers are the same as the old parts) to quite large problems (like we need to install a third emergency diesel generator). And everything in between. The safety equipment gets tested every month, someone needs to watch the results for slow degradation over time. The NRC inspector has questions, someone needs to provide the answers. Another plant found a problem with valves from XYZ company -- someone needs to see if we have the same valves. Operations department says this pump sounds funny. There is a small crack in this pipe support...
If you work inside the plant you will learn how to get dressed up to prevent you from contaminating yourself, and you will go into places and see things that your fellow students will never see.
One thing is, when these problems come up they will call you in, even if it is in the night, and you have to drag yourself into work.
If you have any interest in it, an internship is the very best thing you could do. And even if you don't end up in the nuclear power business, it will be a very cool way to spend a few months.