Nuclear reactors, and particularly those used for the generation of electricity, pollute the environment by their thermal and radioactive discharges. The radioactive discharges may be considerably magnified as a result of reactor accidents, faulty safety precautions, faulty construction or human error. These considerations make it very difficult to select suitable sites for reactors.
In the case of thermal discharges, nuclear plants may inject over 60% more heat to the condenser cooling water than do the most modern fossil-fuelled plants of the same size. Radioactive pollution from a nuclear reactor is created by fission in the reactor core. Some of the radionuclides created by the process escape along various pathways to the environment. The actual emission level depends on the reactor type and the funds invested in containing it. There is disagreement concerning how much radiological pollution from such a source should be officially tolerated.