On the 26th of April 1986 reactor number 4 of the Chernobyl Nuclear Power Plant was destroyed as a result of a failed test. A steam explosion and subsequent fire severely damaged the reactor building.
Two more reactor blocks were under construction at a nearby site, with the reactor 5 finished in about 70% when the explosion occurred. All of the construction work was halted on the 27th of April. Reactor 5 was scheduled to come online around November 1986, less than 6 months after the catastrophe.
More photos from my other visits can be found here: