The secret disaster reportedly took place after a Soviet nuclear weapons test in Kazakhstan during the 1950s, according to Science Alert.
Though the test itself was no secret, a report revels that Soviet scientists discovered widespread radioactive contamination and radiation sickness surrounding the Semipalatinsk test site, but decided to keep it a secret from locals and the rest of the world.
Kazbek Apsalikov, director of the Institute of Biophysics in Moscow, told Fred Pearce New Scientist: ‘For many years, this has been a secret.’
Apsalikov discovered the ‘top secret’ report in the archive of the Russian Institute of Radiation Medicine and Ecology (IRME) in Semey, Kazakhstan, and passed it on to US journalists last week.
He says it details the results of a radiological study of the Semipalatinsk region, where a nuclear disaster four times worse than Chernobyl in terms of the number of cases of acute radiation sickness had occurred in 1956.
The Semipalatinsk Nuclear Test Site (SNTS) is known for being the world’s worst radiation hotspot, where 456 nuclear detonations were carried out between 1949 and 1991.
Though the test in question at the SNTS was conducted underground in tunnels and shafts, the impact of the detonation was felt some 248 miles away and 638 people ended up going to hospital with radiation sickness.
In addition, one million people were later recognised by the government of Kazakhstan as having suffered ‘in a broad sense’, according to a 2014 report by the Norwegian Institute of International Affairs.
That’s reportedly more than four times the 134 radiation sickness cases diagnosed after the Chernobyl disaster.
As Pearce explains, the researchers found that a month after another disastrous 1956 test, radiation rates were still up to 100 times what the report classifies as the “permissible rate”.
The report also revealed that scientists who had conducted expeditions to eastern Kazakhstan had recommended the immediate halt of eating local grain, based on “considerable radioactive contamination of soils, vegetable cover, and food”, but this does not appear to have been acted on.