Chernobyl victim. Ukrainian girl being tested for thyroid cancer caused by the fallout from the Chernobyl nuclear disaster. On 26th April 1986 reactor number 4 of the Chernobyl nuclear power plant in Ukraine, exploded causing huge amounts of radiation to enter the atmosphere. It is considered the worst nuclear power plant disaster in history. A sarcophagus surrounding the reactor was erected by December 1986 and a 30km exclusion zone was set up shortly after. The health consequences of the disaster are poorly understood. In the main hospital in Kiev, Ukraine, 35,000 people are being studied to determine the true effects.