Did Matt groening work at a nuclear power plant?
No he doesn't. He works/worked as the creator of the Simpson's.
Why do you think he works at a nuclear power plant?
Few specifics have been supplied by Matt Groening regarding the Springfield Nuclear Power Plant. The nuclear assembly was cited as a Fissionator 1952 Slow-Fission Reactor, but beyond that, we can only guess. It presents all the appearances of the pressurized water reactor plant with which we are somewhat familiar, as these are the most common types in the US.