In which country was the first nuclear reactor that produced electricity built?
On June 27, 1954, the Obninsk Nuclear Power Plant in the USSR became the world's first nuclear power plant to generate electricity for a power grid, producing around 5 megawatts of electric power.
Construction started on 1 January 1951. First criticality was achieved on 6 May 1954, and the first grid connection was made on 27 June 1954. For around four years, until the opening of the Siberian Nuclear Power Station, Obninsk remained the only nuclear power reactor in the Soviet Union; the power plant remained active until 29 April 2002 when it was finally shut down.