Mayak, Techa River and Lake Karachay

The Mayak complex, near the closed city of Ozersk, started up in 1948 to make weapons plutonium. Between 1949 and 1956 liquid waste was discharged into the Techa River: more than 100 PBq in all, about 98% of it between December 1949 and November 1951, including some 12 PBq of strontium-90 and 13 PBq of caesium-137 (Standring et al., 2009). In 1950 there were 41 villages with 23,500 inhabitants along the river below the plant, using its water for drinking, irrigation and livestock.

Between 1953 and 1960 about 7,500 people were moved out of 20 villages. From 1951 the waste was diverted to Lake Karachay, a small lake with no outlet. On 29 September 1957 a high-level waste tank exploded (the Kyshtym accident): about 740 PBq was released, the contaminated area is estimated at 15,000–20,000 km², and 10,200 people were evacuated. In 1967, after a drought, wind lifted dried sediment from the shores of Karachay and deposited about 22 TBq over 1,800 km².

Lake Karachay was filled in stages, first with hollow concrete blocks (1978–1986), then with rock; backfilling was completed in November 2015. The plant still reprocesses nuclear fuel. The Techa residents have been followed for decades as an epidemiological cohort, one of the few in the world with long-term low-dose exposure.