A 'defect' found in a structural support of a Heysham A1 pod boiler in June has prompted further inspections in three other UK advanced gas cooled reactors with the same design, EDF Energy reports.
During the Heysham A1 planned statutory outage in 2013, an unexpected result was found during routine ultrasonic inspection of a boiler spine, EDF Energy reported. Each reactor at Heysham A and Hartlepool has eight boiler units, known colloquially as 'pod boilers'. These boiler units are arranged around their associated reactor in four quadrants with each quadrant containing two boiler units. Within each boiler unit are boiler tubes assembled in a coil formation around a central forged metal tube called a boiler spine. The boiler spines support the weight of the tubes around them.
EDF Energy said that no similar results were seen on the other seven boiler spines subjected to equivalent inspections on Heysham A1, or during subsequent equivalent inspections of the boiler spines on Heysham A2 and at Hartlepool. Heysham A1 was returned to service early in 2014 on reduced load with the affected boiler quadrant isolated pending further investigations to confirm the source of the unexpected inspection result.
Subsequent more detailed inspections of the affected boiler spine during an outage on Heysham A1 that commenced in June 2014 have confirmed a defect in the location indicated by the initial findings. Heysham A1 remains shut down while work continues to characterise the nature of the defect, EDF Energy said in August. It is likely to continue to operate on reduced load when it returns to service until a suitable repair strategy can be implemented.
For the other three reactors, EDF Energy said that it has taken a conservative decision to shut down Heysham A2 and Hartlepool for inspections that could take up to eight weeks, despite having no indications of defects in previous boiler spine inspections. EDF Energy's other AGRs are not affected by this issue as they are of a different design.
This initiative is not the first time pod boilers have caused concern. In 2007-9, EDF Energy spent more than £150 million installing restraints to preserve the concrete plugs on top of the pod boilers of all four reactors.
Picture: Drawing of pod boiler showing central structural 'spine'. Image: EDF Energy