NEW cracks in the graphite core have been discovered at Hunterston B raising radiation safety fears and resulting in a prolonged shutdown. The reactor was taken offline on March 9, but is not now due to restart until May 1 at the earliest, more than a month later than originally planned. The Office for Nuclear Regulation (ONR) is assessing whether the cracks render the reactor too dangerous to fire up. Its operator, EDF Energy, insists it will reopen, but critics say it should stay shut. The integrity of the thousands of graphite blocks that make up the reactor core is vital to nuclear safety. They ensure that the reactor can be cooled and safely shut down in an emergency. But bombardment by intense radiation over decades causes the blocks to start cracking. If they fail, experts say, nuclear fuel could overheat, melt down and leak radioactivity in a major accident. Both the ONR and EDF told the Sunday Herald that new cracks had been found at Hunterston reactor number three during inspections in recent weeks, but they wouldn’t say how many, or how significant they were. “We are currently assessing the safety case submitted by EDF after a planned outage identified a number of cracks in the graphite blocks that make up reactor three’s core,” said an ONR spokesman. Before we grant permission to EDF to restart reactor three we will require that an adequate safety case justifying further operation has been made. ONR has to formally permission the restart of the reactor.” The ONR’s decision was still “a number of weeks” away, he added. “We will publish the justification behind our decision once it has been made.” According to EDF’s website, Hunterston reactor three was originally due back online on March 30 after a “graphite inspection outage”. But this has been repeatedly postponed to April 6, April 19, April 24 and now May 1. The company confirmed that it had “discovered cracks in the inspections during the current outage”. It promised to report the details to the local site stakeholder group after the reactor was restarted. “As part of the normal ageing process we expect to see defects occurring in some of the graphite blocks that make up the reactor core of our plants,” said an EDF spokeswoman. This phenomenon is understood and is recognised in our operational safety cases which are agreed with the nuclear safety regulator. We have prepared well for this; we have a £100 million graphite research programme. “Hunterston B remains safe to operate and will be back online once the current outage is completed. We will, as normal, consult with our regulators before returning the reactor to service.” Hunterston reactor three, which has been running since 1976, is one of the oldest of its kind. It’s where “graphite defects are most advanced” and hence has more inspections than other reactors, said the EDF spokeswoman. But Pete Roche, a nuclear critic and consultant in Edinburgh, warned that EDF’s optimism that the reactor will restart could be misplaced. “Cracks could prevent control rods from being inserted causing the nuclear fuel to overheat, potentially resulting in a nuclear accident,” he said. It was “all a bit of a gamble”, he argued. “Hunterston is already 42 years old – when it was only expected to operate for 30 or 35 years. It is clearly time to say goodbye to reactor three.” Expert nuclear engineer John Large also suggested that the reactor should be closed down. “The core at Hunterston may now be in such a poor structural state that its collapse during a relatively modest earthquake could result in a nuclear fuel meltdown and significant radioactive release,” he said. “All that EDF can do is permanently shut Hunterston, there being no alternative means to remedy this very serious situation.” Professor Paul Bowen, a metallurgist from the University of Birmingham who advises the ONR, thought that the body was likely to insist on more frequent inspections rather than reactor closure. “I’m absolutely confident that the regulator will take a very conservative position,” he said. According to Rita Holmes, a local resident who chairs the Hunterston site stakeholder group, people were worried. “The local communities are unhappy that the reactor has any cracks, and certainly not happy that one with a growing number of cracks could be allowed to continue generation,” she said.

Herald 22nd April 2018 read more »