Experiment gone wrong

In the early hours of April 26, 1986, in the model Soviet town of Prypyat, a satellite of the much bigger Chornobyl, workers at a nuclear power plant demobilized the safety systems on the number four reactor, which had come on line only three years previously.

It was a risky experiment to see whether the cooling system could still function using power generated from the reactor alone in the event of a failure in the auxiliary electricity supply.

It could not. There was a massive power surge that blew off the reactor's heavy concrete and metal lid and sent smoldering nuclear material into the atmosphere. Dozens of plant staff died on the spot or immediately afterwards in hospitals. Hundreds of thousands of rescue workers, including Soviet Army conscripts, were rushed to the site to put out the fires, decontaminate it and seal off the damaged reactor by building a concrete shell around it.

At first authorities denied there was a problem. When they finally admitted the truth more than a day later, many thousands of inhabitants simply picked up a few of their belongings and headed off – many of them to the capital of Kyiv, 80 kilometers (50 miles) to the south, never to return.

Iryna Lobanova, 44, a civil servant, was due to get married in Prypyat on the day of the explosion.

"1 thought that war had started," she said. "But the local authorities told us go on with all planned ceremonies. Nobody was allowed to leave the town until the official evacuation was announced on the Sunday" – 36 hours later – "following an order from Moscow," she said. Lobanova went ahead with her wedding – and left the next day with her husband by train.