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 (then the former Kazakh SSR), south of the valley of the Irtysh River. The scientific buildings for the test site were located around 150 km (93 mi) 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 south, some as far as into Karagandy Region.