RE: It’s purpose for being created was to help ween the U.S. off of the use of FOREIGN oil.
While that was one reason for the formation of the Department of Energy, the other big reason was to have one Department handle all aspects of the nation’s nuclear program (from reactors to bombs to disposal of waste). In essence, have a “one-stop shop” where anyone that needed a nuclear expert could go.
That’s why they handled the development and production of our nuclear weapons and currently handle their maintenance. (and would design and build more if we were doing that)
And, I think, they are also responsible for helping develop nuclear power plants. Or at least, having their nuclear scientists set the safety standards.
I had always thought all of that should have been handled by the Atomic Energy Commission which was formed after WW II.