<P> The Chernobyl Nuclear Plant utilized one large, open turbine hall for all four reactors without any separating walls . Each reactor had two turbines . On October 11, 1991, a fire broke out in the turbine hall of Reactor number 2 . The fire began in Reactor number 2's Turbine 4 (ТГ - 4 in Russian) while the turbine was being idled for repairs . A faulty switch caused a surge of current to the turbine, igniting insulating material on some electrical wiring . This subsequently led to hydrogen, used as a turbine coolant, being leaked into the turbine hall "which apparently created the conditions for fire to start in the roof and for one of the trusses supporting the roof to collapse ." The adjacent reactor hall and reactor were unaffected . </P> <P> On February 13, 2013, a 600 - square - metre (6,500 - square - foot) 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 . The roof which collapsed was built after the Chernobyl disaster . It was later repaired . </P> <P> On June 17, 2017, a cyberattack affected the radiation monitoring system and took down the power plant's official website which hosts information about the incident and the area . </P> <P> After the explosion at Reactor N. 4, the remaining three reactors at the power plant continued to operate . The schedule for plant decommissioning is intimately wrapped with the dismantling of Reactor N. 4 and the decontamination of its environs . The Chernobyl New Safe Confinement will have equipment which will make decommissioning relatively incidental to, yet an integral part of, the cleanup of the exploded reactor . The majority of the external gamma radiation emissions at the site are from the isotope caesium - 137, which has a half - life of 30.17 years . As of 2016, the radiation exposure from that radionuclide has declined by half since the 1986 accident . </P>

When did the chernobyl power plant go offline