[en] Nuclear accidents are unexpected events characterized by losing of control over the sources of radiation. This may, , directly or indirectly create a danger to human life, health or property. In certain nuclear accidents, such dangers may be of a limited scope, which means that they constitute a threat only to those persons who work directly with the sources of radiation, or the equipment that comprises such sources, and their immediate working environment. Under certain conditions, as a consequence of major nuclear accidents, the broader population and considerable property might be endangered as well. The way in which nuclear accidents with the sources of ionising radiation may occur, the intensity of doses that may exist in the radiation source environment, the nature and quantities of radioactive materials which might spread in the environment, the level of radiation exposure of the staff and the population due to a nuclear accident - all these may be considerably different in case of a nuclear accident with different radiation sources. Depending on the category of nuclear accident, major environmental pollutant releases are possible in such situations. (author)