An employee walks at the control centre of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





An employee and journalists walk through the corridor of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





A control centre of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





A telephone is seen in a control centre of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





A control panel is seen in a control centre of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





An employee measures the radiation level near a damaged fourth reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





Workers sweep radioactive dust at a nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





A control panel is seen in a control centre of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





An employee walks through the corridor of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





A control panel is seen in a control centre of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





Journalists walk through the corridor of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





Dogs are seen in front of a new Safe Confinement (NSC) structure over the old sarcophagus covering the damaged fourth reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





An employee walks through a pump room of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





A control panel is seen in a control centre of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





An employee walks through the corridor of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





A bus carrying workers leaves in front of a new Safe Confinement (NSC) structure over the old sarcophagus covering the damaged fourth reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





Employees walk through the corridor of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





A general view shows a New Safe Confinement (NSC) structure over the old sarcophagus covering the damaged fourth reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





An employee measures the radiation level as journalists take pictures at a control centre of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)





A visitor holds a butterfly that was found in a pump room of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)