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Reactor 3 at EDF’s Hunterston B nuclear power station will need “additional technical analysis” to support its ongoing safety case assessment.
The work is expected to be completed over the next six weeks.
In an open letter, site director Colin Weir said: “After discussions with Office for Nuclear Regulation (ONR) we have agreed that some additional technical analysis will be completed to support the reactor 3 safety case assessment; it is estimated that this additional work will be completed over the next six weeks.
“Through our interactions with ONR, the steps required to complete the assessment of the reactor 3 case have become much clearer, this has allowed the additional work and the assessment timescales to be better estimated.”
Weir added that the reactor is now due to return to service on 15 January 2020, a date pushed back from 1 October.
Both reactors 3 and 4 were taken offline last year while a team of specialist inspectors from EDF’s own internal independent nuclear assurance team, the Nuclear Safety Committee, as well as the ONR, conducted safety investigations.
In August the Office for Nuclear Regulation (ONR) announced that reactor 4 was safe to begin operating again despite having a cracked core.
Cracked graphite cores – What the ONR says
Over time during reactor operation, the graphite bricks age and their properties change due to interaction with the radiation environment and the reactor coolant. This can lead to the graphite losing weight and the development of cracks in the graphite bricks, both of which are well-known phenomena and have been the subject of significant interest by the industry, academics and the regulators for many decades.
Specifically the inspections focused on whether the cracking observed in reactor’s graphite core would compromise safety requirements. The assessment concluded that an “adequate safety case” had been provided to allow a further 16.025 terawatt-days operation period.
In addition, EDF has worked with academics from the University of Bristol to research a range of scenarios including how the core would be affected by extreme conditions such as a large magnitude earthquake.
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