French utility EDF has resumed operation of unit 5 at its Bugey nuclear power plant after receiving approval from the country’s nuclear safety authority. The reactor had been offline for almost two years whilst tests and repairs were carried out on its containment.
Tests conducted in 2011 during the third ten-yearly inspection of the 880 MWe pressurized water reactor identified a high leakage rate from the inner liner of its containment. The containment was found not to be airtight owing to a corroded seal. In December 2014, Autorité de Sûreté Nucléaire (ASN) ordered more tests to be carried out during the unit’s next maintenance and refuelling outage.
That outage began in August 2015 and Bugey 5 has remained offline since. Further tests indicated a degradation of the leak tightness of the metal coating of the inner liner since the tests conducted in 2011. The latest tests also helped locate the leaks at the bottom of the containment liner.
EDF informed ASN in November 2015 that it planned to make repairs to the unit’s containment with a view to restarting the reactor. In April 2016, the utility submitted details of its investigation into the cause of the leaks and how it proposed to remedy them – by applying a composite coating around the base seal of the containment vessel and use a fluid “protective” lime mortar.
In late March this year, ASN approved EDF’s suggested solution to repairing the containment.
EDF carried out the repairs between 29 March and 15 May 2017. The utility subsequently carried out a new test of the containment, which led to a leakage rate in compliance with the general operating rules. Last month it sent ASN a program for monitoring the effectiveness of the repairs, as well as a plan of action and investigations for searching for residual escape routes through the containment.
ASN published an information note on 24 July saying that it had agreed on 18 July that EDF could restart the unit.
EDF announced on 24 July that Bugey 5 was restarted and reconnected to then grid the previous day.
Source: World Nuclear News