The Mayak Production Association (, , from 'lighthouse') is one of the largest nuclear facilities in the Russian Federation, housing a reprocessing plant. The closest settlements are Ozyorsk to the northwest and Novogornyi to the south. Lavrentiy Beria led the Soviet atomic bomb project. He directed the construction of the Mayak Plutonium plant in the Southern Urals between 1945 and 1948, in a great hurry and secrecy as part of the Soviet Union's atomic bomb project. Over 40,000 Gulag prisoners and POWs built the factory and the closed nuclear city of Ozersk, called at the time by its classified postal code "Forty". Five (today closed) nuclear reactors were built to produce plutonium which was refined and machined for weapons. Later the plant came to specialise in reprocessing spent nuclear fuel from nuclear reactors and plutonium from decommissioned weapons. Once production began, engineers quickly ran out of underground space to store high-level radioactive waste. Rather than cease production of plutonium until new underground waste storage tanks could be built, between 1949 and 1951, Soviet managers dumped of toxic chemicals, including 3.2 million curies of high-level radioactive waste into the Techa River, a slow-moving hydraulic system that bogs down in swamps and lakes. As many as 40 villages, with a combined population of about 28,000, lined the river at the time. For 24 of them, the Techa was a major source of water; 23 of them were eventually evacuated. In the 45 years afterwards, about half a million people in the region have been irradiated in one or more of the incidents, exposing them to up to 20 times the radiation suffered by the Chernobyl disaster victims outside of the plant itself. Investigators in 1951 found communities along the river highly contaminated. On discovery, soldiers immediately evacuated the first downriver village of Metlino, population 1,200, where radiation levels measured 3.5–5 rads/hr (35–50 mGy/hr or 10–14 μGy/s). At that rate, people would get the equivalent of a lifetime exposure to radiation in less than a week. During the following decade, ten additional communities were resettled from the river, but the largest community, Muslumovo, remained. Researchers investigated residents of Muslumovo annually in what has become a four-generation living experiment of people living among chronic, low doses of radioactivity. Blood samples showed its villagers took in caesium-137, ruthenium-106, strontium-90, and iodine-131, internally and externally. These isotopes had deposited in organs, flesh and bone marrow. Villagers