for National Geographic News
At 1:24 a.m. on April 26, 1986, reactor number four of the nuclear power plant in the Ukrainian town of Chernobyl exploded as engineers conducted a test to determine how long the plant's generators could run without power.
It was the greatest technological disaster in history. Burning for ten days, the reactor released a cloud of radioactivity that some experts estimate was equivalent to that of 200 Hiroshima and Nagasaki bombs.
The accident killed at least 30 plant workers, caused the hospitalization of hundreds of others, and exposed millions of people to ionizing radiation. This type of high-energy radiation can break apart molecules and atoms.
But 18 years after the disaster, the true health costs of Chernobyl's radiation bomb are still unknown.
Up to 2,000 children later developed thyroid cancer as a result of radiation. While some experts believe the cancer rate has peaked, others warn that it could take decades for all cancers to be detected.
Thousands of other fatal illnesses have also been blamed on the disaster. Less controversially, it is widely accepted that the accident has caused great economic and psychological hardship, especially among the hundred thousand people who had to be resettled.
"Eighteen years after the Chernobyl disaster, we are still unable to give an exhaustive picture of the consequences of this accident and its health implications," said Denise Adler, a radiation expert at the University of Geneva in Switzerland. "It can't be compared to any other environmental disaster."
Chernobyl is located about 80 miles (130 kilometers) north of Kiev, the Ukrainian capital, and 7 miles (11 kilometers) south of the border with Belarus. At the time of the accident, Ukraine and Belarus were still part of the Soviet Union.
Belarus was affected the most by the Chernobyl catastrophe. About 70 percent of all released radioactive substances from Chernobyl fell on its territory.
Some places in western Europe and Turkey received contaminated rains, and insignificant amounts of radiation even reached the United States. In Switzerland, it is still forbidden to eat mushrooms in some mountainous parts.
The secretive Soviet government at first downplayed the magnitude of the disaster. Few residents were told to evacuate the area, even though a large swath of territory soon became heavily contaminated by radionuclidesatoms that emit ionizing radiation.
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