The Chernobyl disaster was a
nuclear accident
A nuclear and radiation accident is defined by the International Atomic Energy Agency (IAEA) as "an event that has led to significant consequences to people, the environment or the facility. Examples include lethal effects to individuals, lar ...
that occurred on 26 April 1986 at the No. 4
reactor in the
Chernobyl Nuclear Power Plant
The Chernobyl Nuclear Power Plant (ChNPP; ; ), is a nuclear power plant undergoing decommissioning. ChNPP is located near the abandoned city of Pripyat in northern Ukraine northwest of the city of Chernobyl, from the Belarus–Ukraine bor ...
, near the city of
Pripyat in the north of the
Ukrainian SSR
The Ukrainian Soviet Socialist Republic ( uk, Украї́нська Радя́нська Соціалісти́чна Респу́бліка, ; russian: Украи́нская Сове́тская Социалисти́ческая Респ ...
in the
Soviet Union
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
. It is one of only two nuclear energy accidents rated at seven—the maximum severity—on the
International Nuclear Event Scale
The International Nuclear and Radiological Event Scale (INES) was introduced in 1990 by the International Atomic Energy Agency (IAEA) in order to enable prompt communication of safety significant information in case of nuclear accidents.
The ...
, the other being the 2011
Fukushima nuclear disaster
The was a nuclear accident in 2011 at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan. The proximate cause of the disaster was the 2011 Tōhoku earthquake and tsunami, which occurred on the afternoon of 11 March 2011 an ...
in
Japan. The initial emergency response, together with later
decontamination
Decontamination (sometimes abbreviated as decon, dcon, or decontam) is the process of removing contaminants on an object or area, including chemicals, micro-organisms or radioactive substances. This may be achieved by chemical reaction, disinfect ...
of the environment, involved more