The remote Mayak nuclear facility is Russia's oldest and biggest center for manufacturing radioactive isotopes and reprocessing spent nuclear fuel from several nations. Here are some key moments in its history:
1945: Construction begins on the Mayak facility in secrecy under the supervision of Josef Stalin's secret police chief, Lavrentiy Beria.
1948: The first reactor opens, staffed by workers living in a closed town on site.
1949-1956: Mayak workers regularly dump waste into the Techa River, a local source of drinking water and tributary to the Arctic Ocean.
1957: Buried storage tanks for nuclear waste explode, spreading a plume of fallout 300 kilometers (200 miles) long, exposing 217 towns and villages and 272,000 people to radiation.
1967: A nearby lake used for dumping nuclear waste dries up during a drought. Strong winds blow nuclear dust eastward into 68 towns and villages with 42,000 inhabitants.
1993: The Russian government officially acknowledges that about 450,000 people may have been harmed by Mayak fallout since the late 1940s, sign bill into law creating new regime of medical and other benefits.
1994: The closed town hosting Mayak is placed on official maps for the first time and given the place name Ozersk.
2001-2004: At least 30 million cubic meters (1 billion cubic feet) of radioactive waste is released into the Techa River. Mayak's director is convicted in 2005 of illegal dumping.