Chernobyl disaster environmental research. Scientists measuring the radiation levels in a forest contaminated by the Chernobyl nuclear disaster. On 26th April 1986 reactor number 4 of the Chernobyl nuclear power plant 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. Here, they have cut small trees down and will measure how far radiation has penetrated into their trunks during their growth.