It was doable back in the day, especially if nuclear plant workers make as much as the OP says.
My family was exactly like the Simpsons in terms of what we could afford growing up and who was working. Although my dad worked in an auto factory as opposed to a nuclear plant. He was first a line worker but then managed to be trained to repair machinery.
In the year 2024, it’s hard to fathom how that was at all possible to do, but times were different back then. I will say, I’m fairly certain that my parents were also in a ton of debt when I was growing up. It’s just that they used to give loans to everyone (hence the housing market crash in around 2009 or whenever it was).