Nuclear engineering is the branch of engineering concerned with the application of the breakdown (fission) as well as the fusion of atomic nuclei and/or the application of other sub-atomic physics, based on the principles of nuclear physics. In the sub-field of nuclear fission, it particularly includes the interaction and maintenance of systems and components like nuclear reactors, nuclear power plants, and/or nuclear weapons. The field also includes the study of medical and other applications of (generally ionizing) radiation, nuclear safety, heat/thermodynamics transport, nuclear fuel and/or other related technology (e.g., radioactive waste disposal), and the problems of nuclear proliferation.