The impossibility of constructing a technological facility that would function in a completely safe way is a well-known fact. Various failures and accidents are almost common occurrence in their everyday work. On the other hand, major disasters in technological facilities do not happen very often, but when they do happen, they usually leave serious consequences.

Accidents in technological facilities can happen as results of failures or human mistakes. They can also be caused by external influences like earthquakes, floods, extreme meteorological conditions or terrorist attacks.

Accidents in nuclear facilities are specific because they can leave considerable radiological consequences as a result of the presence of huge amounts of radioactive material. They can endanger human health and contaminate the nature surrounding the area of the facilities.

In case of an accident, emission of radioactive material from a nuclear facility into the surrounding area can come about. Radioactivity can be emitted into the atmosphere, surface-waters or soil, that is, underground waters. The experience so far has pointed out that special attention should be paid to the accidents with major emission of radioactivity into the atmosphere followed by a considerable emission of warmth.

Should an emission of radionuclides from the facilities into the atmosphere occur, a so-called radioactive cloud would be formed. It would then expand under the influence of very complex processes in the atmosphere.

A population affected by the radioactive cloud would first be exposed to direct radiation from the radioactive cloud and breathing in of radioactive particles and gasses contained in the cloud. In a later phase, after the deposition of the particles on the surface, the prevailing ways of exposing would consist of direct radiation from the deponed radioactive material, breathing in of the resuspended dust and consuming of the contaminated food and water.

Until our days a few minor and major accidents have occured in nuclear power plants. The most notorious ones are the following:

1957 Windscale, England
(reactor for production of plutonium)

1957 Kyshtym, Russia
(spent nuclear fuel processing facility)

1973 Windscale, England
(spent nuclear fuel processing facility)

1979 Three Mile Island, USA
(nuclear power plant)

1980 Saint-Laurent, France
(nuclear power plant)

1986 Chernobyl, Ukraine
(nuclear power plant)

1989 Vandellos, Spain
(nuclear power plant)

1999 Tokamura, Japan
(nuclear fuel processing facility)