An army tank fires during a firefight against militants linked to al Qaeda near the southern Yemeni city of Zinjibar May 30, 2012. (Photo by Reuters/Yemen's Defence Ministry)

The Chernobyl disaster was a catastrophic nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine, which was under the direct jurisdiction of the central authorities of the Soviet Union. The Chernobyl disaster is the worst nuclear power plant accident in history in terms of cost and resulting deaths, and is one of only two classified as a level 7 event (the maximum classification) on the International Nuclear Event Scale (the other being the Fukushima Daiichi nuclear disaster in 2011). Photo: Graffiti of a crying baby on a wall, Chernobyl Power Plant, Chernobyl, Ukraine. (Photo by Hans Neleman/Getty Images)

An unknown number of guns are being built with the mechanisms, causing problems for the police and ATF officials. Photo: An ATF agent holds a generic unfinished receiver, back, and one that has been manufactured, front, at an ATF field office in Washington, on May 06, 2014. The ATF is trying to crack down on the trade in the makeshift guns by targeting shops and individuals who offer to turn the unfinished receivers into functional pieces for firearms. (Photo by Bill O'Leary/The Washington Post)

A rescuer saves a resident from a flooded area in Wuhan, Hubei Province, China, July 2, 2016. (Photo by Reuters/China Daily)

Children ride in the trunk of a car on a flooded street in Sanaa, Yemen August 1, 2016. (Photo by Khaled Abdullah/Reuters)

Pine trees are seen after a forest fire near Sao Pedro do Sul, Portugal August 14, 2016. Deadly wildfires raging for two weeks in Portugal have destroyed a wooded area the size of 100,000 soccer fields, and the small Iberian nation alone accounts for half of all forests burned in the European Union this year. (Photo by Rafael Marchante/Reuters)

Children try to push an injured and weak dolphin back into the water after it washed ashore during bad weather and high tide on a beach in Cilacap, Central Java, Indonesia August 12, 2016 in this photo taken by Antara Foto. (Photo by Idhad Zakaria/Reuters/Antara Foto)

A resident looks at a wildfire in Vina del Mar, Chile, March 12, 2017. Forest fires are a regular feature of Chile's hot, arid summers, but a nearly decade-long drought combined with historically high temperatures have created tinder-like conditions in the nation's central regions. (Photo by Rodrigo Garrido/Reuters)