The potential dangers of a nuclear installation, including a nuclear power plant, are contamination and irradiation.
There is no "zero risk". This goes for nuclear energy as well as for all human activities. In order to bring the theoretical risk as close to zero as possible, the design and managing of a nuclear power plant are founded on the "defense in depth" concept, a principle systematically applied on all levels.
The point is that a series of barriers are put in place, comparable to the famous Matrioshka ("Russian dolls"): if the first one fails, the second one intervenes; and should the second one refuse to work, then the third one takes over, and so on.
In the same way as the scale used for determining the intensity of an earthquake, the INES scale (International Nuclear Events Scale) wants to inform the public on the seriousness of events in the nuclear industry. "Incidents" come under levels 1 to 3, "accidents" under levels 4 to 7.
Within the framework of the program for « experience feedback » :
• each relevant event is systematically analyzed and classified on the INES scale
• if need be, actions are taken in order to prevent the repetition of such an event
• an international communication system provides an effective exchange of information on the events and the actions taken.