This precautionary measure was taken after the discovery of a crack on a component known as a boiler spine[i] at Heysham 1. Hartlepool power station was also shut down because both stations share the same unique design with each of its 16 boilers supported by this boiler spine component.
Other advanced gas-cooled reactors in the UK have a different and more conventional boiler design without a boiler spine and they are manufactured from different materials. Therefore there is no risk that they could suffer from the same issue.
Since then, EDF Energy has put in place a detailed and fully resourced boiler inspection programme at both sites and further boiler inspections are now underway. This has involved working with key suppliers to identify and put the necessary equipment and people in place to undertake this complex and specialised engineering programme.
Engineers have recently been able to begin their inspections and the first two inspections have been completed. The engineers found no defects on these spines.
EDF Energy has identified that to bring these reactors back into service, the programme must:
- Complete the inspections to verify there are no further defects which could develop into cracks
- Understand in detail the cause of the crack found on the boiler spine at Heysham 1
- Develop detailed designs and techniques for modifications to mitigate the impact of any defects
- Then implement modifications if necessary
During the coming weeks the programme team will focus on completing the inspections and work to build a robust case for the safe continuing operation of the boilers. This “safety case” is subject to approval from the independent nuclear regulator, the ONR (Office for Nuclear Regulation).
Now that the programme has been developed in detail and is underway, EDF Energy can give information on the estimated dates for returning the four reactors to service. Depending on the progress of the programme and any necessary modifications, the company expects there to be a phased return to service between the end of October and the end of December, 2014.
Dates for returning the stations to service depend on the findings and completion of the inspections. EDF Energy will give further updates on the progress of the programme when it is able.
EDF Group has already identified actions to mitigate the financial impact of the lower nuclear output.