Spent fuel pond. We used to say the place you can get a tan without going outside.
When the rods are taken out of the reactor for replacement, they transfer them to the spent fuel pond for temporary storage. The boron water suppresses the reaction and keeps the surrounding area and people from being irradiated.
There are spent fuel pond divers. This is gradually being replaced by underwater drones but the divers are still around. Another occupational joke in the nuke utility business was that you had to pass psych exams to get NRC security clearance. They never gave those tests to the divers because it is understood they are all crazy.
Rods that come out of the pool to make room for more rods go into permanent, specialized concrete casks stored outside. That storage yard BTW is guarded by very tight security and men with automatic weapons.
I didn't do that kind of work but volunteered once to work in the containment during an outage at Peach Bottom in PA. It's strictly volunteer. You suit up, go in, put a wrench on a nut and turn it until your 60 seconds is up. Then out you go and the next guy comes in to repeat that procedure until all the nuts are loose and the valve can be removed. Crazy. As B'ster mentioned, everyone wears dosimeters. Nuke plant workers are allowed to absorb a certain umber of RADs per year. If I remember right it's 50 mSv (millisieverts) . Or at least back then it was. Radiation sickness symptoms become observable at somewhere around 1000 mSv.
Every worker who is allowed into hot areas is tracked by the NRC in cooperation with the utilities. They know what your exposure is. Once you hit your annual dose limit, you cannot work anywhere hot.