The F-1 (from "First Physical Reactor") is a research reactor operated by the Kurchatov Institute in Moscow, Russia. When started on December 25, 1946, it became the first nuclear reactor in Europe to achieve a self-sustaining nuclear chain reaction.[1] It was still in operation in the beginning of the 2010s, with a power level of 24 kW, making it, at that time, the world's oldest operating reactor.