EDF Energy says it has shut down four of its UK reactors after discovering a fault in a boiler spine in unit 1 of its Heysham 1 nuclear power plant - "although routine inspections of other boiler spines have not previously indicated any similar defects."
|Heysham 1 (Image: EDF Energy)
In a statement issued today, EDF Energy said it shut down the Heysham unit in June and then took 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." The units are expected to remain closed for two months.
Each reactor at Heysham 1 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.
"During the Heysham 1 Reactor 1 planned statutory outage in 2013, an unexpected result was found during routine ultrasonic inspection of a boiler spine," the company said.
"No similar results were seen on the other seven boiler spines subjected to equivalent inspections on Heysham 1 Reactor 1, or during subsequent equivalent inspections of the boiler spines on Heysham 1 Reactor 2 and at Hartlepool (the design of the boilers being unique to Hartlepool and Heysham 1)," it said.
Heysham 1 unit 1 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 the unit that started in June have confirmed a defect in the location indicated by the initial findings, the company said.
The unit remains shut down while work continues "to characterise the nature of the defect," EDF Energy said. "Until the results of the further inspections are known it is not possible to advise exact return to service dates for these four reactors, however, an initial estimate is that these investigations will take around eight weeks," it said.
Heysham 1 and Hartlepool power stations are of a unique design in the EDF Energy nuclear fleet and the continued safe operation of our other nuclear power stations is not impacted, it said.
Heysham 1 unit 1 is likely to continue to operate on reduced load when it returns to service until a suitable repair strategy can be implemented, the company said.
The likely maximum theoretical output before unplanned losses for the EDF Energy Nuclear Generation Fleet between 1 January and 31 December inclusive will be about 61 TWh, it said.
Researched and written
by World Nuclear News