Nazarbaev made the remarks at the 21st congress of the Kazakh Trade Union Federation in the capital Astana.
The Semipalatinsk range, located in northeastern Kazakhstan, was the former Soviet Union's main atomic weapons test site. Between 1949 and 1989, more than 460 nuclear explosions were conducted there.
Soviet citizens living near the site were exposed to several above-ground tests, and these people and their descendants have suffered from birth defects, high rates of cancer, and other serious illnesses.
Environmentalists say there are several inhabited areas of Semipalatinsk that still have radiation levels unsafe for humans.