1986 reactor #4 catastrophe[edit]

Further information: Chernobyl disasterThe Chernobyl #4 reactor was catastrophically destroyed on 26 April 1986. This photo was taken of the ruins of Chernobyl Nuclear Power Plant Reactor #4 during the construction of the Sarcophagus in the late summer of 1986.

On 26 April 1986, the Chernobyl disaster occurred at reactor No. 4, caused by a catastrophic power increase resulting in core explosions and open-air fires. This caused large quantities of radioactive materials and airborne isotopes to disperse in the atmosphere and surrounding land.A helicopter sprays a decontamination liquid^{[citation needed]} nearby the Chernobyl reactor on 13 June 1986

The disaster has been widely regarded as the worst accident in the history of nuclear power. As a result, Reactor No. 4 was completely destroyed, and therefore enclosed in a concrete and lead sarcophagus, followed more recently by a large steel confinement shelter, to prevent further escape of radioactivity. Large areas of Europe were affected by the accident. The radioactive cloud spread as far away as Norway.^[17]

The plant utilized one large, open turbine hall for all four reactors without any separating walls. Each reactor had two turbines.

In February 2013, a 600 square metres (6,458 sq ft) portion of the roof and wall adjacent to the covered part of the turbine hall collapsed into the entombed area of the turbine hall. The collapse did not affect any other part of the Object Shelter or the New Safe Confinement. No variances in radiation levels as a result of the incident were detected.^[18] The collapsed roof was built after the Chernobyl disaster, and was later repaired.^[19]