Chernobyl

Just outside the small Soviet town of Pripyat, in what is now northern Ukraine, stood the Chernobyl nuclear power station — four huge reactors that lit homes and powered factories across the region. Pripyat itself was a model town: new, clean and young, built for the plant's workers and their families, with an average age under thirty. On the night of 25 April 1986, the engineers at Reactor No. 4 prepared for a safety test. The idea sounded sensible enough. If the power ever failed, would the reactor's own spinning turbines keep the vital cooling pumps running for the few seconds before the backup generators kicked in?

To run the test they had to take the reactor down to very low power — and there the trouble began. The RBMK reactor, the Soviet design used at Chernobyl, behaved dangerously when run slow, and the men at the controls had not been told just how unstable it could become. Worse, to keep the test going they switched off safety systems and pulled out almost all the control rods that normally calm the reaction. Shortly after one in the morning on 26 April, the reactor's power surged out of control in seconds. An operator slammed the emergency shutdown — but on this flawed design, that final button made things worse, not better.

Two enormous explosions tore the top off Reactor No. 4. The thousand-tonne lid was thrown aside, the roof was blown open, and the burning core was left exposed to the night sky, pouring radiation straight into the air. Firefighters arrived within minutes, knowing there was a blaze but not that they were standing in an invisible storm of radiation. Many received fatal doses that night. Of the workers and firefighters taken to hospital, 28 would die within months of acute radiation sickness.

And yet, in Pripyat, life carried on at first. Children went to school. People hung out washing in air that was already poisoned. For a day and a half the authorities said almost nothing. Only on the afternoon of 27 April — some 36 hours after the explosion — did the buses arrive. Around 47,000 residents were told to pack a small bag for "a few days." Within hours the town got evacuated, and its people were driven away. They never came back. Pripyat stands empty to this day: a ghost town of silent flats, a rusting fairground, and a swimming pool with no water.

The Soviet government said nothing to the wider world. Then, on the morning of 28 April, alarms began sounding at the Forsmark nuclear plant in Sweden, more than a thousand kilometres away. Staff there checked their own reactor for a leak and found none — the radiation was blowing in on the wind, from the east. When Sweden demanded answers, Moscow could no longer stay silent, and that evening it finally admitted, in a few brief sentences, that there had been an accident at Chernobyl. Even then the truth was held back. The scale of the disaster was said to have been hidden for days, and in nearby Kyiv the May Day parades went ahead as planned, with thousands marching beneath an invisible cloud.

The clean-up became one of the largest operations of its kind in history. Hundreds of thousands of workers — soldiers, miners and volunteers, the so-called liquidators — were sent in to bury contaminated soil, wash down streets, and build a vast concrete "sarcophagus" over the ruined reactor in just a few months. A 30-kilometre exclusion zone was sealed off around the plant, and it remains in place today. It is now believed that many workers got exposed to dangerous doses of radiation, and the long-term health toll is still argued over. Above all, the disaster shattered public trust: a secretive system had hidden a catastrophe from its own people, and many historians see Chernobyl as one of the cracks that helped bring down the Soviet Union itself.