In 1957, the Mayak plant was the site of a major disaster, one of many
other such accidents. An improperly stored underground tank of
high-level liquid nuclear waste exploded, contaminating thousands of square kilometers of land, now known as the Eastern Ural Radioactive Trace (EURT). The matter was covered up, and few either inside or outside the Soviet Union were aware of the full scope of the disaster until 1980. Before the 1957 accident, much of the waste was dumped into the
Techa River, which severely contaminated it and the residents of dozens of riverside villages such as Muslyumovo, who relied on the river as their sole source of drinking, washing, and bathing water. After the 1957 accident, dumping in the Techa River officially ceased, but the waste material was left in convenient shallow lakes near the plant instead, of which 7 have been officially identified. Of particular concern is
Lake Karachay, the closest lake to the plant (now notorious as
"the most contaminated place on Earth" over several decades. On 29 September 1957, Sunday, 4:22 pm, an explosion occurred within stainless steel containers located in a concrete canyon deep used to store high-level waste. The explosion completely destroyed one of the containers, out of 14 total containers ("cans") in the canyon. The explosion was caused because the cooling system in one of the tanks at Mayak, containing about 70–80 tons of liquid
radioactive waste, failed and was not repaired. The temperature in it started to rise, resulting in evaporation and a chemical explosion of the dried waste, consisting mainly of
ammonium nitrate and acetates. The explosion was estimated to have had a force of at least 70
tons of TNT. The explosion lifted a concrete slab weighing 160 tons, and a brick wall was destroyed in a building located from the explosion site. A tenth of the radioactive substances were lifted into the air. After the explosion, a column of smoke and dust rose to a kilometre high; the dust flickered with an orange-red light and settled on buildings and people. The rest of the waste discarded from the tank remained at the industrial site. The workers at Ozyorsk and the Mayak plant did not immediately notice the contamination. In the first hours after the explosion, radioactive substances were brought into the city on the wheels of cars and buses, as well as on the clothes and shoes of industrial workers. After the blast at the facilities of the chemical plant, dosimetrists noted a sharp increase in the
background radiation. Many industrial buildings, vehicles, concrete structures, and railways were contaminated. The most polluted were the city's main thoroughfare, named after Leninits centrality was especially significant when entering the city from the industrial siteand Shkolnaya Street, where the management of the plant lived. Subsequently, the city administration imposed measures to stop the spreading of contamination. It was forbidden to enter the city from industrial sites in cars and buses. Site workers at the checkpoint got off the buses and passed the checkpoint. This requirement extended to everyone, regardless of rank and official position. Shoes were washed on flowing trays. The city was intentionally constructed to be upwind from the Mayak plant given the
prevailing winds, so most of the radioactive material drifted away from, rather than towards, Ozyorsk. There were no immediate reported casualties as a result of the explosion; however, the scope and nature of the disaster were covered up both internally and abroad. Even as late as 1982,
Los Alamos published a report investigating claims that the release was actually caused by a weapons test gone awry. The disaster is estimated to have released of radioactivity. Most of this contamination settled out near the site of the accident and contributed to the pollution of the
Techa River, but a plume containing of radionuclides spread out over hundreds of kilometers. Previously contaminated areas within the affected area include the Techa river, which had previously received of deliberately dumped waste, and Lake Karachay, which had received . In the next ten to eleven hours, the radioactive cloud moved towards the north-east, reaching from the accident. The
fallout of the cloud resulted in long-term contamination of an area of , depending on what contamination level is considered significant, primarily with
caesium-137 and
strontium-90. The land area thus exposed to radioactive contamination was termed the "East Ural Radioactive Trace" (EURT). About 270,000 people inhabited this area. == Evacuations ==