>the lifespan of a camera module was about 24-48 hours for work inside the water of the reactor near the "hot" fuel of the reactor

Wow, you must have needed many shelves full of replacements ready. The whole thing has me curious and full of questions.

How did they even go about replacing them without endangering anyone? And why was a camera needed in a place so close that they would fail so quickly?

It was literally a guy's job on the floor to just replace modules and other electronics. The equipment itself would not become contaminated so it was safe to handle afterwards. It just got bombarded by radiation and became useless as a camera. Being hit by ionizing radiation does not mean you become radioactive. The main issue is if bits of contamination would stick to our fancy duct tape we had around the cameras.

As for why we needed them it's for a bunch of reasons. This is 30 meters down. You gotta inspect welds, replace jet pumps, pick crap up that people drop in, pull plugs, help guide CRD maintenance. Tons of stuff. You gotta see it all. Camera handlers are magical and learn to swim the cameras around using puppet like movements. You manipulate these duct taped to rope cameras using either the cable or the rope. Sometimes we would attach them to stupendously long poles we assemble which were also duct taped (this changed eventually). The issue is such a long pole is basically a pool noodle in terms of handling. Keeping stuff from getting stuck and having confidence in where you were was an art. I wish I could tell you nuclear inspection used fancy drones and super high tech robotics but a ton of the visual side is duct taped cameras and talented handlers. Ultrasonic inspection is where the robotics took over and where they earn their keep. Encoding the position is worth the effort. But for visual you can't really get a sub to do much better than a guy with a long pole. Haha