Alarm after serious breakdowns at ageing Hunterston nuclear plant

Monday, October 13, 2014

One of the reactors at the ageing Hunterston nuclear power station in North Ayrshire has been plagued by two serious new breakdowns.

Two large gas circulators vital for cooling the reactor and preventing meltdown were damaged when the lubricating oil was mistakenly switched off. And on Thursday the reactor had to be shut down because its turbine generator was shaking more than it should.

These latest mishaps come after the discovery of two new cracks in the reactor's graphite bricks, as well as a rash of nuclear incidents across Scotland during the 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 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.

"After they've stopped producing their last expensive electricity, nuclear power leaves a hazardous and expensive legacy. After the past week, anyone who thinks it has any role to play in Scotland's energy future should reconsider."

The two gas circulators at Hunterston, each the size of a bus, were so badly damaged by the lack of lubrication they had to be replaced. They were being used to cool reactor four while it was shut down for maintenance and inspections.

The reactor was powered up again last Sunday but on Thursday it had to be shut down because of intense vibrations. The French state company that runs the Hunterston B nuclear plant, EDF Energy, stressed there had been no safety consequences, though repairs 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. It was a human error and we're disappointed but we've responded by putting in measures to prevent it happening again."

Then in a letter to the Hunterston site stakeholder group on Friday, Weir disclosed that reactor four had to be taken off-line again on Thursday because of "increased vibrations on the turbine generator". He added: "We took this conservative decision to allow investigation."

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. "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 extra pressure while it assesses the 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, with a risk of a fire in the reactor core, Large said. "This could have run on to serious in-reactor consequences."

Rita Holmes, who chairs the Hunterston site stakeholder group, questioned EDF's view that the plant could operate safely until 2023. "I am extremely concerned 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 problems. "We should 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 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 but a spokeswoman said the development showed that "Scotland's nuclear facilities have a limited lifespan" .

There were three other incidents last week. On Tuesday, a fire on the MV Parida, carrying waste from Dounreay to Belgium, led to the evacuation of the Beatrice oil platform and at Dounreay a fire was found in a sodium store. The Scottish Environment Protection Agency is also looking into excess emissions of the radioactive gas, tritium, from the defunct Chapelcross nuclear station near Annan.

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