The UK's Office for Nuclear Regulation (ONR) has said it is satisfied that EDF Energy is taking "appropriate and conservative action in the interests of continued nuclear safety" in its decision to shut down its reactors at the Heysham 1 and Hartlepool sites. The closures are in response to the identification of unexpected "cracking" in a boiler spine of unit 1 at Heysham 1, ONR said.
EDF Energy informed ONR soon after it detected a defect with the boiler unit of reactor 1 at Heysham 1 last October, company spokesman Gordon Bell told World Nuclear News today. ONR gave permission for the utility to isolate the boiler unit and operate the reactor as normal when it returned to service on 1 January until it was able to take it offline and inspect it fully, which it did in June, Bell said.
Each reactor at Heysham 1 and Hartlepool has eight boiler units, which are arranged around their associated reactor in four quadrants with each quadrant containing two boiler units.
"ONR was satisfied we could run the reactor safely with that boiler isolated," Bell said.
"By June, we had worked out a strategy for investigating the defect and we then put out a press release to local media and newswires stating that we were going in to the reactor to refuel and to take the opportunity to carry out boiler investigations," he said.
EDF Energy is unable to give an exact description of the defect yet, but it is certain that it is on the boiler spine, which supports the weight of the boiler tubes. Bell said. "We found an unexpected result during routine ultrasonic inspections and later identified this as a defect, but we need to wait until we complete our investigations," he said. The ONR has described this defect as a "crack".
Asked why the company thinks the defect may affect some reactors and not others, Bell said: "Heysham 1 and Hartlepool are the same design type of advanced gas-cooled reactors, and the design of those is unique. This issue does not impact our other advanced gas-cooled reactors because they are of different design."
In EDF Energy's fleet, only Heysham 1 and Hartlepool are of the exact same design and started operating in the same year – 1983.
The inspections will look to establish whether the defect with the boiler spine is related to the design, manufacture or operations process.
The defect has been found in one boiler at Heysham 1's unit 1. Bell said, "We will now carry out investigations of the other three reactors over an estimated period of eight weeks and will then know more as a result."
Asked if the defect may affect the lifetime operation of reactor 1 at Heysham 1, Bell said: "We have a strategy across our nuclear power stations to seek life extension where it is safe and commercially viable to do so."
The company completed shutting down the four reactors this morning, meaning output has been lost totalling 1155 MWe at Heysham 1 and 1180 MWe at Hartlepool, he said.
EDF Energy is not expected to provide a further update on the boiler investigation until it has been completed.
Researched and written
by World Nuclear News