On 26 April 1986, it was decided at Chernobyl to take advantage of reactor number four’s downtime by carrying out a safety test on an emergency core cooling feature.
At 1.24 am, an engineer recorded in his diary that the protective system was not working. At the same moment, a huge and catastrophic surge in power caused two explosions.
As fires raged, the core of reactor number four was destroyed. A huge cloud rose into the sky, spreading large amounts of radioactive fuel and materials into the atmosphere.
Sweden was the first foreign country to find out about the accident, when it detected unusual levels of radioactivity coming from the east two days later.
Ukrainian authorities tried to hide the disaster, which had, by that time, claimed only two lives. One power station employee was killed instantly and another died in hospital several hours later.
Firefighters who rushed to put out the blaze were not properly equipped and suffered radiation poisoning. Attempts were made to cool the reactor by dropping 4,000 tons of lead and sandbags onto the site.
Around 48,000 people living in Pripyat were also victims of the ineptitude and secrecy of the authorities. The town was only three kilometres away from Chernobyl. Evacuation from Pripyat began a full day and a half after the explosion.
Investigations into the accident at Chernobyl revealed both procedural and design errors at the nuclear facility.