The test required reactor activity and the thermal reactor output to be run down to a lower level. During the procedure, however, the reactor plummeted to an unexpectedly low and unstable level of activity. At this point, it should have been shut down; as the operators chose to continue with the test, the events subsequently proved to be catastrophic.
More than 200 people died or were seriously injured by radiation exposure immediately after the explosion. 161,000 people had to be evacuated from a 30 kilometer radius of the reactor and 25,000 square km of land were contaminated. As time went on millions of people suffered radiation related health problems such as leukemia and thyroid cancer and around 4,000 people have died as a result of the long-term effects of the accident.
Nobody was prepared for such a crisis. For the next seven months, 500,000 men will wage hand-to-hand combat with an invisible enemy – a ruthless battle that has gone unsung, which claimed thousands of unnamed and now almost forgotten heroes. Yet, it is thanks to these men that the worst was avoided; a second explosion, ten times more powerful than Hiroshima which would have wiped out more than half of Europe. This was kept secret for twenty years by the Soviets and the West alike.