Right, because generators the size needed to operate nuclear power plants are the sort of thing that you just pick up at any corner hardware store and "drive up and plug in"?
here's what one of those generators looks like. A nuclear power power plant may have a dozen or more in their generator building. Even replacing just one is not some sort of couple day task. These things take prep work and a lot of labour to acquire, move, install and set up. Weeks to months. That's all assuming that the generator building itself is still usable; a failure in such a large generator, or the sort of external event that can take out such a large generator, is not exactly some sort of low energy event.
Back before Fukushima people like you were all over Slashdot harping about how major nuclear disasters couldn't happen again, that it's only possible with old Soviet designs like Chernobyl that are horribly misused. Quit being so damned short sighted. Unforseen events and cascading failures do happen. You can't just act like "the list of causes of major that have already happened is the entire comprehensive list of what could cause major failures".
If you scram, lose your grid connection and lose your generators, you will likely get a Fukushima-like event. Two of the three happened here. Let's not pretend that the concept of something taking out the generator room, or otherwise preventing its power from working the pumps - generators which are only rarely tested - is such a preposterous concept. And let's not be silly and act like massive pieces of industrial equipment can just be plopped down and hooked up like a little Honda generator.