This article focuses on the environmental impact of nuclear energy and addresses the following major environmental issues associated with nuclear power generation: ① controlling the radioactive discharge from nuclear installations under normal operation and evaluating their non-radioactive environmental impact (water withdrawals and non-radioactive discharges); ② long-term management of spent fuel and radioactive waste (radwaste), notably that disposed off in geological repositories; ③ prevention and mitigation of severe nuclear accidents and their radioactive releases and; ④ improving nuclear safety to restrict its environmental impact and to contribute toward the public acceptance of nuclear energy. Nuclear energy, with its very low emissions of green house gases, has a unique capacity to generate massive and on-demand dispatchable amounts of electricity. The annual effective radiation dose delivered to the public surrounding nuclear power plants under normal operation is negligible. Considerable efforts have been made to define sustainable management of high-level long-lived radwaste that is disposed in geological formations. The return of experience from severe nuclear accidents in the past has informed and propelled major improvements in several aspects of nuclear energy production—including reactor design and operational management as well as in the development of accident-management guidelines— and has proved to be highly valuable. The environmental risks in the event of a severe accident have been substantially reduced and protocols have been established to minimize the release of radioactive materials and avoid the large-scale evacuation of people in the event of a severe nuclear accident. Efforts must be continued to improve reactor safety and enhance the transparency of the industry and the authorities that support and control nuclear power to further reduce the environmental impact.