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Cracks in Scots reactor highlight UK's ageing nuclear fleet

Hunterston b nuclear power station (geograph 5851877)

Cracks in the graphite reactor blocks at Hunterston B might not pose a safety risk, but they do highlight the age of the UK’s fleet of nuclear reactors, and the worrying lack of projects in the pipeline to bolster the sector.  

Photos of cracks up to 2mm wide in both of the Scottish plant’s reactors have been published for the first time. It comes one year after the nuclear reactors in North Ayrshire were shut down for detailed inspections following the discovery of cracks in the graphite bricks used in the reactor cores, and the advance gas-cooled reactors (AGR) remain offline.   

EDF, who operate the 1,000MW plant, has stressed that the cracks, which measure 2mm across, are within acceptable limits and are “a known phenomenon” for the type of reactor technology given its age and do not pose a safety risk. Cracks under 10mm are considered acceptable under EDF’s internal regulations.     

However, AGRs account for 14 of the 15-strong fleet in the UK and provide almost 20% of the UK’s energy. Consequently, nuclear regulators have warned that the same “life limiting” cracks at Hunterston, and previously Hinkley Point B, could mean other plants are taken offline.  

hunterston b crack

Hunterston B crack

Source: EDF Energy

This image shows one of the cracks in the graphite at Hunterston, this particular crack measures 2.9mm across

Cornwall Insight analyst Peter Atherton - who specialises in energy projects - previously told The Guardian that if Hunterston remained offline it would leave a “big hole” in energy supplies, and it would take time to plug the gap with new infrastructure such as renewables.  

“Let’s say worst-case scenario they found a big graphite core problem and Hunterston never comes back on,” he said. “That would be a big hole in the plan [for electricity supplies]. The gas-fired power stations, we’ve probably got enough of them, but it would be pretty tight. It would also be a knock-back to carbon targets. You could build more windfarms, but that would take time.” 

The cancellation of the NuGen project in Cumbria and suspension of work on the new plant at Wylfa Newydd on Anglesey has already raised concern about the future energy supply for the UK, a problem that will become all the more real should a portion of the AGR fleet need to be taken offline before their scheduled decommissioning.  

The problem of cracks in AGR cores isnt a new one, but once the cracks become significant, they pose a serious risk of preventing engineers from safely stopping the nuclear reaction inside the plant cores. 

A spokesperson for the Office of Nuclear Regulation (ONR) told New Civil Engineer that cracks “will eventually be life limiting to the AGRs in the UK”.   

The ONR spokesperson added that the regulatpr had rejected an application to restart one of Hunterston’s reactors in November, and that the safety case was pending. “The safety case for a return to service of Reactor 4 was received in November 2018 and our preliminary assessment indicated that an adequate safety case had not yet been made,” they said. “EDF is developing further evidence, relating to multiple cracked bricks, to support the Reactor 4 safety case.”   

The graphite bricks in an AGR act as a moderator and allow for the nuclear reaction to be sustained. The bricks also provide a vital safety function, providing structure through which carbon dioxide flows to remove heat from the fuel inside the reactor, and through which the control rods needed to shut down the reactor are inserted. 

EDF is working on providing new safety evidence to the ONR, and expects both Hunterston reactors will resume service once signed off by the ONR.  

The UK’s aging nuclear reactor fleet;

Name Technology Type Process  Capacity (MW) Grid Connection Date Load Factor 2017 Generated to date (GW/h) 

Sizewell B 

SNUPPS 

PWR 

1198 

1995-02-14 

83.9 

8,805 

Torness 2 

AGR 

GCR 

595 

1989-02-03 

93.1 

4,853 

Heysham B 2 

AGR 

GCR 

615 

1988-11-11 

96.2 

5,182 

Heysham B 1 

AGR 

GCR 

615 

1988-07-12 

94 

5,066 

Torness 1 

AGR 

GCR 

590 

1988-05-25 

78.5 

4,057 

Dungeness B 2 

AGR 

GCR 

525 

1985-12-29 

73.1 

3,363 

Hartlepool A 2 

AGR 

GCR 

585 

1984-10-31 

90.6 

4,642 

Heysham A 2 

AGR 

GCR 

575 

1984-10-11 

64.9 

3,269 

Hartlepool A 1 

AGR 

GCR 

595 

1983-08-01 

89.6 

4,673 

Heysham A 1 

AGR 

GCR 

580 

1983-07-09 

59.9 

3,044 

Dungeness B 1 

AGR 

GCR 

525 

1983-04-03 

51.2 

2,357 

Hunterston B 2 

AGR 

GCR 

485 

1977-03-31 

80.5 

3,421 

Hinkley Point B 1 

AGR 

GCR 

480 

1976-10-30 

90.6 

3,810 

Hunterston B 1 

AGR 

GCR 

480 

1976-02-06 

91.8 

3,861 

Hinkley Point B 2 

AGR 

GCR 

475 

1976-02-05 

83.8 

3,485 

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Readers' comments (1)

  • Unless the Govt get their finger out, arrange more successful methods of funding and support for major projects, we are going to have more and more energy woes. We will end up reverting to fossil fuels/less environmentally friendly methods of energy production unless we can get serious about build the next generation of Nuclear Reactors, seriously step up our offshore wind production and invest in emerging technologies (Small Modular Reactors, battery storage, decentralised energy production and storage). A lot going on in this country at the moment but this must take a priority for the good of all.

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