Investigations into potential cracks in boiler spines at two units at each of the Heysham I and Hartlepool sites are likely to take until the end of the year to complete, EDF Energy has announced.
On 11 August, the company said it had shut down Heysham I unit 1, in northwest England, in June after discovering a fault in a boiler spine and taken the "conservative decision" to halt the second reactor there, and two at its Hartlepool site in the northeast of England, "which are of a similar design." At that time, EDF Energy said it expected the units to remain closed for about two months while investigations are carried out.
However, the company has now announced that "a detailed and fully resourced boiler inspection program" has begun at the four advanced gas-cooled reactors (AGRs) which will take longer than original envisaged. EDF Energy said this has involved "working with key suppliers to identify and put the necessary equipment and people in place to undertake this complex and specialized engineering program."
Each reactor at Heysham I and Hartlepool has eight boiler units. These boilers are arranged around their associated reactor in four quadrants with each quadrant containing two boilers. Within each boiler are 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.
.jpg "AGR boiler spine 460 (EDF Energy)") |
| Each boiler comprises a complex array of boiler tubes with a central cylindrical boiler spine that provides structural support to the tubes (Image: EDF Energy) |
EDF Energy said that the first two boiler inspections have been completed and that no defects had been found on these spines.
The company said it will not restart the reactors until inspections have verified that there are no further defects in the boiler spines and that the cause of the crack found at Heysham I unit 1 is fully understood. It will also develop modifications "to mitigate the impact of any defects" and implement them if necessary.
EDF Energy's director of engineering Mark Hartley said, "The inspections "will give us confidence there is no cracking in any of the other boilers and ensure that they are safe to continue operating. At that point we will through our own very stringent safety assessment processes develop our safety justification. We will then present this to the Office for Nuclear Regulation for their approval."
He added, "This would allow us to return the four units to power, but recognizing at this stage that the boiler where we have observed some cracking will remain shut down and isolated."
EDF Energy said, "Depending on the progress of the program 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."
Researched and written
by World Nuclear News
Originally posted on www.world-nuclear-news.org on 04 September 2014, manyt thanks to WNN for permission to repost.