Kyshtym disaster

The Kyshtym disaster (Russian: Кыштымская авария), sometimes referred to as the Mayak disaster or Ozyorsk disaster in newer sources, was a radioactive contamination accident that occurred on 29 September 1957 at Mayak, a plutonium reprocessing production plant for nuclear weapons located in the closed city of Chelyabinsk-40 (now Ozyorsk) in Chelyabinsk Oblast, Russia in the Soviet Union. 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 for nearly two decades. The disaster is the second worst nuclear incident by radioactivity released, after the Chernobyl disaster, and was regarded as the worst nuclear disaster in history until Chernobyl. It is the only disaster classified as Level 6 on the International Nuclear Event Scale (INES). It is the third worst nuclear disaster by population impact after the two Level 7 events: the Chernobyl disaster, which resulted in the evacuation of 335,000 people, and the Fukushima Daiichi disaster, which resulted in the evacuation of 154,000 people. At least 22 villages were exposed to radiation from the Kyshtym disaster, with a total population of around 10,000 people evacuated. Some were evacuated after a week, but it took almost two years for evacuations to occur at other sites. The disaster spread hot particles over more than 52,000 square kilometres (20,000 sq mi), where at least 270,000 people lived. Since Chelyabinsk-40 (later renamed Chelyabinsk-65 until 1994) was not marked on maps, the disaster was named after Kyshtym, the nearest known town.

Background After World War II, the Soviet Union lagged behind the United States in the development of nuclear weapons, so its government started a rapid research and development program to produce a sufficient amount of weapons-grade uranium and plutonium. The Mayak plant was built in haste between 1945 and 1948. Gaps in physicists’ knowledge about nuclear physics at the time made it difficult to judge the safety of many decisions. Environmental concerns were secondary during the early development stage. Initially, Mayak dumped high-level radioactive waste into a nearby river, which flowed to the river Ob, flowing farther downstream to the Arctic Ocean. All six reactors were on Lake Kyzyltash and used an open-cycle cooling system, discharging contaminated water directly back into the lake. When Lake Kyzyltash quickly became contaminated, Lake Karachay was used for open-air storage, keeping the contamination a slight distance from the reactors but soon making Lake Karachay the "most-polluted spot on Earth". A storage facility for liquid nuclear waste was added around 1953. It consisted of steel tanks mounted in a concrete base, 8.2 meters (27 ft) underground. Because of the high level of radioactivity, the waste was heating itself through decay heat (though a chain reaction was not possible). For that reason, a cooler was built around each bank, containing twenty tanks. Facilities for monitoring operation of the coolers and the content of the tanks were inadequate. The accident involved waste from the sodium uranyl acetate process used by the early Soviet nuclear industry to recover plutonium from irradiated fuel. The acetate process was a special process never used in the West; the idea is to dissolve the fuel in nitric acid, alter the oxidation state of the plutonium, and then add acetic acid and base. This would convert the uranium and plutonium into a solid acetate salt.

Explosion On 29 September 1957, Sunday, 4:22 pm, an explosion occurred within stainless steel containers located in a concrete canyon 8.2 m (27 feet) 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 200 meters (660 ft) 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. There were no immediate reported casualties as a result of the explosion.

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