The U.K.'s Office for Nuclear Regulation gave permission to restart Reactor 4 at Scotland's Hunterston B power station having been offline for a year due to safety concerns, operator EDF Energy said on Tuesday.
Two out of four of the plant's reactors were shut down last year when hundreds of cracks were found in the graphite bricks within the reactor cores.
After a comprehensive investigation, the nuclear regulator determined that "Reactor 4 is safe to operate for the next period and can be safely shut down in all foreseeable circumstances, including that of a significant seismic event."
Reactor 4 has been allowed to operate for a four-month period, with the regulator saying the longer-term condition of the reactor "remains uncertain" while EDF Energy "will need to justify safe operation" beyond the four-month period.
EDF Energy said tests had "demonstrated that even in the most extreme conditions our reactors operate within large safety margins," adding the control rods will "safely shut down the reactor in all circumstances."
As per the regulator's request for the reactor’s continued safety screening, EDF Energy said, "It is important that we continue to monitor the core and so will perform frequent graphite inspections. These will enable us to continue to demonstrate that the reactor operates with large margins to ensure safe operation at all times."
Reactors 1 and 2 of the power plant are currently being decommissioned. The third reactor remains offline since it was shut down in March 2018, however, EDF Energy submitted the safety case for its return to service to the regulator for their consideration.
By Zeynep Beyza Kilic