The Semipalatinsk Test Site (Russian: Семипалатинск-21; Semipalatinsk-21), also known as "The Polygon", was the primary testing venue for the Soviet Union's nuclear weapons. It is located on the steppe in northeast Kazakhstan (in the former Kazakh SSR), south of the valley of the Irtysh River. The scientific buildings for the test site were located around west of the town of Semipalatinsk (later renamed Semey), near the border of East Kazakhstan Region and Pavlodar Region, with most of the nuclear tests taking place at various sites further to the west and the south, some as far as into Karagandy Region. The former Soviet Union conducted 456 nuclear tests at Semipalatinsk from 1949 until 1989 with little regard for their effect on the local people or environment. The full impact of radiation exposure was hidden for many years by Soviet authorities and has only come to light since the test site closed in 1991. According to estimates from Kazakh experts, 1.5 million people were exposed to fallout over the years. From 1996 to 2012, a secret joint operation of Kazakh, Russian, and American nuclear scientists and engineers secured the waste plutonium in the tunnels of the mountains. Since its official closure on 29 August 1991, the Semipalatinsk Test Site has become the best-researched nuclear testing site in the world, and the only one in the world open to the public year-round. History The site was selected in 1947 by Lavrentiy Beria, political head of the Soviet atomic bomb project (Beria falsely claimed the vast 18,000 km² steppe was "uninhabited"). Gulag labour was employed to build the primitive test facilities, including the laboratory complex in the northeast corner on the southern bank of the Irtysh River. The first Soviet bomb test, Operation First Lightning (nicknamed Joe One by the Americans) was conducted in 1949 from a tower at the Semipalatinsk Test Site, scattering fallout on nearby villages (which Beria had neglected to evacuate). The same area ("the experimental field", a region west of Kurchatov city) was used for more than 100 subsequent above-ground weapons tests. Later tests were moved to the Chagan River complex and nearby Balapan in the east of the STS (including the site of the Chagan test, which formed Chagan Lake). Once atmospheric tests were banned, testing was transferred to underground locations at Chagan, Murzhik (in the west), and at the Degelen mountain complex in the south, which is riddled