sudden and unexpected event or series of events due to the development of an uncontrolled chain reaction or to the uncontrolled escape of radioactive material, any accident involving facilities or activities from which a release of radioactive material occurs or is likely to occur and which has resulted or may result in an international significant transboundary release that could be of radiological safety significance for another State, a major and unintentional nuclear event, or a series of nuclear events, that is caused by the development of an uncontrolled chain reaction or the uncontrolled release of radioactive material and that leads to significant consequences for people, the environment or the nuclear facility, äkiline ja ootamatu sündmus või sündmuste jada, mist tekib kontrollimatu ahelreaksiooni või kontrollimatu radioaktiivse materjali lekke tõttu