F-1 became Europe’s first nuclear reactor

On December 25, 1946, Moscow’s F-1 research reactor, led by physicist Igor Kurchatov, reached criticality: a controlled, self-sustaining nuclear fission chain reaction began inside it. The Kurchatov Institute identifies it as Europe’s first nuclear reactor; Rosatom’s history calls it the first in Europe and Asia. F-1 was a research reactor, not a power station.