In late May NII issued agreements to allow start up of reactors at three power stations: Hinkley Point B, Hunterston B and Oldbury.
Following detailed assessment, NII concluded that the boiler tube integrity cases for the Hinkley Point B/Hunterston B reactors are adequate for restarting the reactors. Accordingly, Licence Instruments have been issued to enable Reactors 3 and 4 at both stations to be restarted. The reactors will be restarted at reduced operating temperatures to minimise the potential for any further degradation arising from the creep damage mechanism that caused the defects discovered by inspections in the 2006 outages. Furthermore the safety cases define initial periods of operation limited to between 7 and 16 months before the reactors are shut down for further inspections. The reactors are being restarted in sequence to allow adequate time for the benefit of the revised operating conditions to be assimilated.
A Licence Instrument has also been issued to permit Reactor 2 at Oldbury to be restarted, following detailed consideration of the case for its graphite core. Shortly after its restart the reactor was shut down by the operators due to an explosion in a high voltage bushing of the turbine generator transformer, which is located outside of the turbine hall. There were no injuries and the type of plant, a large transformer, similar to transformers used at conventional electricity generating stations, poses no radiological danger. The longer term consequences for restart are still to be determined.