The atoms of plutonium or whatever break down into other atoms. This process is called fission. When it breaks down it also lets neutrons loose, which then attach to other plutonium atome, destabilizing it, then the next one and so on in a chain reaction that produces heat. That heat is transferred to water, which the eventually powers steam turbines. Electricity does not come directly from the rods.
This whole process is regulated via neutrons(or maybe protons, not 100% on that). Put the rods of plutonium closer together, get more fission, more heat. I think they use graphene to regulate things too.
Probably left to work for the new administration. Probably make a great Secretary of education. Get those test scores up