Ukraine ousted Khrushchev and became the Soviet leader from 1964 to 1982. Many prominent Soviet sports players, scientists, and artists came from Ukraine. On 26 April 1986, a reactor in the Chernobyl Nuclear Power Plant exploded, resulting in the Chernobyl disaster, the worst nuclear reactor accident in history. This was the only accident to receive the highest possible rating of 7 by the International Nuclear Event Scale, indicating a "major accident", until the Fukushima Daiichi nuclear disaster in March 2011. At the time of the accident, 7 million people lived in the contaminated territories, including 2.2 million in Ukraine. After the
Russian military intervention in Ukraine (2014–present) sphere of interest. Iulian Chifu and his co-authors claim that in regard to Ukraine, Russia pursues a modernized version of the Brezhnev Doctrine on "limited sovereignty", which dictates that the sovereignty of Ukraine cannot be larger than that of the Warsaw Pact prior to the demise of the Soviet sphere of influence. This claim is based on statements of Russian leaders that possible integration of Ukraine into NATO would jeopardize Russia's national security. After the collapse of the Soviet Union, both nations retained very close ties. At the same time, there were several sticking points, most importantly Ukraine's significant nuclear