28 mai 2013
Le réacteur n° 2 a été mis à l’arrêt suite à la découverte de vibrations sur le stator de l’alternateur principal. Ce gros alternateur, qui peut fournir 840 millions de watts, est refroidi par de l’hydrogène.
1ère divergence : août 1987 - type : PWR - P : 885 MW
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Qu’il soit affirmé qu’il n’y avait pas de problème de sécurité nucléaire n’est pas sérieux : en effet l’accident mortel du 31 Mars 2013 (Voir cet accident ci-dessous dans le dossier "risque nucléaire") sur le réacteur d’Arkansas concernait des travaux dans la salle des machine du réacteur n° 1.
La chute d’un stator a entrainé indirectement l’explosion d’un disjoncteur dans la zone protégée et la perte de toutes les alimentations électriques du réacteur.
Nuclear reactor in forced shutdown By Rachel Morgan rmorgan@timesonline.com |
SHIPPINGPORT — A reactor at the Beaver Valley Nuclear Power Station was shut down Tuesday morning in a rare forced outage caused by a malfunctioning generator.
A spokesman for the Nuclear Regulatory Commission confirmed that Unit 2 was taken offline by plant operator FirstEnergy because of vibrations in the main generator. The vibrations resulted from parts in the main generator stator, a stationary part of the rotary system used in an electric generator, that had either broken or become loose, said Neil Sheehan of the NRC.
“Remember that these machines rotate at 1,800 rpm and will have some wear from actual mechanical vibrations, as well as from repeated heating and cooling cycles,” he said.
“The generators are large electrical components that are cooled by hydrogen.”
The shutdown of the 846-megawatt reactor subtracted 0.2 percent from the nation’s electric grid, moving nationwide nuclear power production to 84 percent capacity, according to NRC data compiled by Bloomberg. As of Tuesday evening, the reactor remained offline, NRC data showed.
The NRC’s resident inspectors for the Shippingport plant “will keep close watch on the company’s efforts to troubleshoot the vibration issue as well as any repairs that are made,” Sheehan said.
Unit 2 is a pressurized water reactor, which means that steam created in the plant’s steam generators is piped to the turbine to spin it and, via the generator, converts that energy to electricity that is then sent out into the grid, officials said. Unit 2 came online in 1987. The plant’s other reactor, Unit 1, came online in 1976.
FirstEnergy officials said they shut down Unit 2 early Tuesday “to perform maintenance after higher than expected vibrations caused the main generator to operate less efficiently than normal.”
While Sheehan said the forced shutdown wasn’t a nuclear safety issue, it was necessary.
“The unit had to be shut down to address the vibration issue affecting the generator,” he said. “From our perspective, it’s not a nuclear safety issue. Both nuclear and other types of power plants have turbine generators.
“Nevertheless, we’re interested in the troubleshooting and any repairs involving the generator because a turbine trip (shutdown) can trigger a reactor shutdown, which the control room operators would then have to cope with.”
While both the main generator and the reactor are located inside the plant’s protected area, FirstEnergy spokeswoman Jennifer Young said the main generator is part of the non-radioactive electrical generation equipment in the plant.
Young did confirm the outage was unplanned, but she said there was no risk to public safety.
“These vibrations pose no risk to public health or safety,” she said. “A team is assessing the cause of the increased vibrations, and repairs will be completed to ensure the generator is in optimal condition for reliable summer performance.”
Sheehan agreed, saying the unit has since been removed from service and the generator has stopped rotating and generating electricity.
“There would have been no radiation release from this problem, (because) turbines and generators are on the non-nuclear side of the plant, so public health and safety have not been affected,” he said.
Young said that for competitive reasons, the company will not say how long the reactor is expected to be offline.
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