Four years ago, on April 26, 2016, the 30th anniversary of the Chornobyl nuclear disaster was commemorated in Ukraine and around the world.
In the early morning hours, sirens sounded in Ukraine to mark 30 years since the moment that the first explosion blew the roof off the building housing a reactor at the Chornobyl nuclear power plant that sent a cloud of radioactive material high into the air, drifting into Russia and Belarus, and across northern Europe.