Obtain a bachelor's degree in nuclear engineering with a minor in physics. Nuclear engineering is the study of nuclear reactions and the mechanisms available to capture energy from those reactions. This is a very difficult course of study, and it is not uncommon for it to take five years instead of four. The physics minor is very helpful in order to understand the framework within which nuclear reactions occur.
Obtain a PhD in nuclear engineering. Nuclear energy is a very complex topic, and a bachelor's degree is not sufficient to fully understand it. Grad student status is also necessary to obtain access to many nuclear labs where new discoveries are made. In addition, the contacts you make in grad school are helpful in finding a job in the nuclear industry and are a good source of recommendations for your security clearance.
Obtain a security clearance. The Nuclear Energy Act of 1954 made all patents related to atomic energy and weapons property of the United States government, and the government requires security clearances to access a lot of its data pertaining to nuclear energy. The level of clearance will depend on the level of access you need at your job. This will require an in-depth background check, criminal record check and fingerprinting. A conviction for any felony and some misdemeanors can lead to instant revocation of your clearance.
Subscribe to nuclear energy scientific journals such as "Progress in Nuclear Energy" and "Atomic Energy." Because this field is on the cutting edge of science, new discoveries are made every day. It is even better if you contribute to the journals and aide others in their understanding of nuclear energy.