Nuclear energy is attracting revived interest as a potential alternate for electric power generation in the event of increased concerns about global warming. Compared to energy produced by combustion of a carbon atom in coal, fission of a U-235 atom will produce about 10 millions times more energy. However, storage of the nuclear waste is an environmental issue. This chapter has four sections with a major focus on introduction of nuclear power plants and reprocessing of spent nuclear fuels. Different nuclear fuel cycles and nuclear power reactors are introduced in the first section, and the cost–benefits of different energy sources are compared. Fuel burnup and formation of fission products are discussed along with operational impacts and risk analyses in the second section. The third section discusses design of nuclear structural components and various degradation modes. Section four discusses reprocessing issues of nuclear spent fuels. Reprocessing of spent nuclear fuel may be an economically viable option and reduces high-radioactive load in the nuclear waste repositories as well. However, there is a concern about proliferation of weapons-grade plutonium separated during reprocessing. Containment of radionuclides in different waste forms is also discussed in this section.