Chernobyl: The Explosion Came Before the State Told the Truth

In the early hours of 26 April 1986, Pripyat in northern Ukraine was still asleep. A few kilometres away, Unit 4 at the Chernobyl nuclear power plant was being prepared for a test. Engineers wanted to know whether a spinning turbine could keep the cooling pumps running after the outside power supply was cut, while the diesel generators started. It was meant to be a safety test, not an attack and not an unexpected event from outside the plant.

The test was carried out on an RBMK-1000 reactor whose weaknesses were not fully explained to the people operating it. When water in the core turned into steam, the reaction in this type of reactor could rise instead of fall. Its control rods also had graphite displacers at their tips. When they were inserted rapidly in a particular state, those tips could briefly increase power. Those two details turned an ordinary test into a chain of rising power that the crew could no longer stop.