Chernobyl disaster environmental research. Researcher checking probes in a well dug in the earth near the Chernobyl sarcophagus. 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. These probes are situated in the 'red forest' 2km from the sarcophagus and well within the exclusion zone. They are part of a French-German project studying how far radionucleotides have penetrated into the earth in the years following the disaster.