You don't have to work at a power plant... Assuming you're a student, try doing an internship at a national lab like LANL or ORNL, or contact physics or mechanical engineering professors at your university to see if there's research you're interested in.
The only thing I know how on the basis of nuclear reactor design is how to run kcode in MCNP and see if my theoretical reactor is critical. How would I be able to calculate how the fuel is burning in my reactor over some period of time, and change my core composition accordingly?