from Sunday Herald, 12 October 2014
One of the reactors at the ageing Hunterston nuclear power station in North Ayrshire has been plagued by two serious new breakdowns, the Sunday Herald can reveal.
Two large gas circulators vital for cooling the reactor and preventing meltdown were badly damaged because someone mistakenly switched off the oil meant to lubricate them. And on Thursday the reactor had to be unexpectedly shut down after running for just four days because its turbine generator was shaking more than it should.
These latest mishaps come after the discovery of two worrying new cracks in the reactor’s graphite bricks, as well as a rash of nuclear incidents across Scotland last week. A ship carrying radioactive waste caught fire and went adrift in the Moray Firth, there was a fire at the Dounreay nuclear complex in Caithness and excess emissions of radioactive tritium gas came under investigation at Chapelcross in Dumfries and Galloway.
Critics say the Hunterston plant, which opened in 1976, is showing its age and question plans to keep it running until at least 2023. “Last week served up examples of pretty much everything that is wrong about nuclear power,” said Lang Banks, director of the environmental group, WWF Scotland.
“Even long after they've stopped producing their last bit of very expensive electricity, nuclear power leaves a hazardous and very expensive legacy. After the past week, anyone who thinks it has any role to play in Scotland's energy future should reconsider their position.”
The two gas circulators at Hunterston, each the size of a coach, were so badly damaged by the lack of lubrication that they had to be replaced. They were being used to cool reactor four while it was shut down for maintenance and safety inspections.
The reactor was allowed to power up again on 5 October, with eight gas circulators running as usual to prevent it from overheating. But on 9 October it had to be shut down again because of unusually high turbine vibrations.
The French state company that runs the Hunterston B nuclear plant, EDF Energy, stressed that there had been no safety consequences, though replacing the circulators had cost £100,000. “During the recent period of planned maintenance at Hunterston B, some bearings on two running gas circulators were damaged because lubricating oil was switched off in error,” said the station’s director, Colin Weir.
“We chose to replace them and completed the job before the unit was switched back on at the beginning of October. It was a human error and we’re disappointed that this happened but we’ve immediately responded by learning from the mistake and putting in measures to prevent it happening again, including adding it to our human performance training programme.”
Then in a letter to the Hunterston site stakeholder group on Friday, Weir disclosed that reactor four had to be manually taken off-line again on Thursday morning because of “increased vibrations on the turbine generator”. He added: “We took this conservative decision to allow investigation and any necessary repairs to take place.”
The gas circulator failures are also under investigation by the government’s Office for Nuclear Regulation (ONR), which pointed out that emergency back-up cooling had been available. “ONR is continuing to follow up this event, but the cause of the low lubricating oil pressure has been attributed to human performance error,” said a spokeswoman.
The independent nuclear engineer, John Large, pointed out that ONR was under pressure because of the work it was doing to assess the various designs of new nuclear stations planned for England and Wales. The simultaneous failure of two gas circulators would “prove to be a very costly mistake,” he predicted.
The loss of gas cooling could cause fuel pins to melt and fail, with a risk of a fire in the reactor core, Large said. “This was a relatively serious incident that could have run on to serious in-reactor consequences.”
Rita Holmes, who chairs the Hunterston site stakeholder group, questioned EDF’s optimism that the plant could carry on operating safely until 2023. “Whilst I have every faith in the Hunterston B workforce and management, I am extremely concerned about the latest developments and well past the stage of reassurance from EDF being enough.”
The Green MSP, Alison Johnstone, accused the nuclear industry of being quick to play down its problems. “We should take every opportunity to phase out outdated plants like Hunterston and have transition plans in place for the local economies,” she said.
It was reported last week that two “keyway root cracks” had been found in the 6,000 graphite bricks in the core of Hunterston reactor four. According to a technical report released by ONR, this was significant because they were a new phenomenon, previously predicted by EDF to be “potentially life limiting”.
The Scottish government said it had been assured by ONR that Hunterston B continued to be safe to generate electricity. “At the same time, this development does illustrate that Scotland’s nuclear facilities have a limited lifespan and we need to put in place longer term energy alternatives,” said a spokeswoman.
“That is why the Scottish government is opposed to the building of new nuclear capacity in Scotland, as it would divert billions of pounds away from renewable alternatives where Scotland has a key competitive advantage.”
On top of the problems at Hunterston, Scotland was hit by three other nuclear incidents last week. The most serious was an engine fire on the MV Parida on Tuesday evening while she was carrying radioactive waste from Dounreay across the sea to a nuclear plant in Belgium.
The ship started drifting in the Moray Firth, and the nearby Beatrice oil platform was evacuated as a precaution. The Parida was towed ashore, repaired and on Friday set sail for Belgium again.
In the early hours of Tuesday morning a fire also flared up in a sodium store at the Dounreay plant, and is now under investigation. Another probe has been launched by the Scottish Environment Protection Agency into excess emissions of the radioactive gas, tritium, from the defunct Chapelcross nuclear station near Annan.
This old steel mill electrician has (non-nuclear) experience with motors, gearboxes and lube oil pumps. Shutting off lube oil pumps to operating equipment is fairly stupid. That lube oil flow switches did not immediately signal an alarm and get people to restart pumps before equipment damage is beyond incompetent. Really? TMI, Chernobyl, Fukushima, who will be next?
Posted by: David Gaeddert | 16 October 2014 at 12:02 AM