An invisible atomic legacy
Between 1949 and 1989, the Soviet Union conducted 456 nuclear tests at the Semipalatinsk Test Site, an 18,000 square kilometer area of steppe known locally as "The Polygon". Of these, 116 were atmospheric tests, detonating on towers or dropped from aircraft, which ceased after the 1963 Limited Test Ban Treaty. The remaining 340 tests occurred in underground tunnels and boreholes. The first test, codenamed "First Lightning" (RDS-1), occurred on August 29, 1949, and had a yield of 22 kilotons. The total explosive power unleashed over four decades was 2,500 times greater than the bomb dropped on Hiroshima.
This intensive testing left a persistent radiological landscape. The explosions vaporized nuclear fuel, which then condensed into microscopic "hot particles." These particles were carried by wind and settled over the landscape, contaminating soil, water, and vegetation with a cocktail of radionuclides. The most significant long-term contaminants are isotopes of plutonium, primarily plutonium-239 (Pu-239) and plutonium-240 (Pu-240). Pu-239 has a half-life of 24,110 years, while Pu-240 has a half-life of 6,561 years, ensuring their presence in the environment for millennia. These isotopes emit alpha particles, heavy, short-range radiation which is particularly damaging if inhaled or ingested.
Mapping the contamination
The distribution of plutonium across The Polygon is not uniform. The highest concentrations are found at the "Experimental Field," the site of the early atmospheric tests. Radioactive fallout from these tests contaminated an estimated 300,000 square kilometers, an area the size of Germany, and exposed approximately 1.5 million people to radiation. Studies have measured elevated concentrations of Pu-239, Pu-240, and Americium-241 (a decay product of Plutonium-241) in the topsoil, where they remain largely concentrated in the upper 10 centimeters.
One of the most dramatic features is Lake Balapan, also known as the "Atomic Lake." It was created on January 15, 1965, by the detonation of a 140-kiloton device in a 178-meter deep hole in the dry bed of the Chagan River. The explosion formed a crater 400 meters in diameter and 100 meters deep, which subsequently filled with water. This was part of a Soviet program called "Nuclear Explosions for the National Economy," intended to use atomic blasts for civil engineering projects.
After the site's official closure on August 29, 1991, large quantities of fissile material were left unsecured in tunnels and boreholes. Between 1996 and 2012, a secret, 17-year joint operation between Kazakhstan, Russia, and the United States secured enough plutonium for dozens of nuclear weapons at a cost of $150 million. Today, the National Nuclear Center of Kazakhstan manages the site, conducting research on radioecology and non-proliferation.