 With the cessation of nuclear testing and the decommissioning of the test site, Kurchatov's population has fallen from over 20,000 to around 8,000.In its heyday Kurchatov (which was known by its postal code Semipalatinsk-21) was a closed city, one of the most secretive and restricted places in the Soviet Union.The nuclear facilities at Kurchatov are managed by the Kazakhstan Institute of Atomic Energy, a division of the country's National Nuclear Center.