Fewer inspections for Vt. Yankee steam dryer
BRATTLEBORO — The Nuclear Regulatory Commission has approved a request by Entergy Nuclear to reduce the number of inspections for Vermont Yankee’s steam dryer, which has proved to be a major source of problems at other similar reactors that have undergone a boost in power production.
Under the change, Entergy Nuclear will inspect the steam dryer — a large steel plate above the reactor — every three outages, or once every 4½ years. Currently, Entergy Nuclear has been checking the steam dryer during every outage, which occurs every 18 months.
Neil Sheehan, a spokesman for the Nuclear Regulatory Commission, said Friday that since Vermont Yankee had undergone the 20 percent power boost, there have been no serious problems uncovered with the steam dryer.
While there have been 65 new cracks identified in the steam dryer since 2006, Entergy determined that 39 of the cracks were “non-relevant.” Entergy also said that many of the cracks were pre-existing to the power boost, but that they were only revealed because of improved technology.
Sheehan said Entergy had reinforced the steam dryer and would continue to monitor the dryer. If problems come up, there will be additional inspections, said Rob Williams, a spokesman for Entergy Nuclear.
Sheehan said the three-outage inspection schedule was the standard for similar boiling water reactors.
Regular inspection of the steam dryer was a condition set by the NRC when Entergy Nuclear ramped up power production at Yankee in 2006.
Serious problems had been uncovered at Quad Cities nuclear power plant in Illinois in 2002, with a portion of its steam dryer breaking off and lodging in steam lines. The problems were caused by increased vibration of plant components from the boost in power production, and the increased vibration broke metal components that had been damaged by intergranular stress-corrosion cracking, a well-known problem in nuclear power plants.
The steam dryer removes moisture from steam as it leaves the reactor and heads toward the turbine.
Williams said the new inspection schedule was the industry standard. “We’ve demonstrated we have a good handle on this condition and that will continue,” he said.
He said that Entergy would inspect the steam dryer using guidelines established by the Electric Power Research Institute. But he said Entergy was adopting a “more conservative” frequency of inspection, since EPRI only suggests inspection every seven outages, roughly every 10 years.
“We’ll increase the frequency, if necessary, based on the results, as required by the NRC,” he said.
He said inspecting the steam dryer involves specialized equipment, and must be done by a special contractor.