BRATTLEBORO — The Vermont Yankee nuclear plant sprung another radioactive leak Thursday, this time in a more safety-sensitive area of the plant.
Power production at the reactor was reduced to about 40 percent by 4 p.m. in order to allow the immediate repairs to the seemingly small leak in a feedwater line.
Robert Williams, spokesman for Entergy Nuclear, said the leak amounted to "60 drops a minute," but warranted immediate attention.
Meanwhile, officials from both the Nuclear Regulatory Commission and the state of Vermont said that Entergy Nuclear could learn exactly how serious the leak is later Thursday evening, when workers are scheduled to remove the insulation on the 24-inch pipe which is leaking radioactive water.
"Entergy will have a sense of the significance of the leakage after it gets a closer look at the line tonight," NRC spokesman Neil Sheehan said Thursday.
"It is important to learn the cause of the leaking to assure it isn't caused by something like flow-accelerated corrosion," said Sarah Hofmann, director of public advocacy for the Department of Public Service.
Corrosion of piping is an industrywide problem at nuclear reactors, particularly older plants.
It is the second leak in as many days disclosed by the owners of Vermont's only nuclear plant, and officials appeared to be taking the feedwater line leak much more seriously than the earlier, but larger, leak in a clean-out line. Both leaks involved radioactive water coming from different systems in the plant.
"We're coming down to 40 percent," Williams said midafternoon, while declining to say exactly how radioactive the water was that was leaking.
The feedwater line provides water to the reactor, which turns it into steam, which is piped to the turbines, which generate the electricity.
Williams said the water was "mildly" radioactive. Entergy had called the level of radioactivity in the earlier leak as "slight." He said there was no release of radioactivity outside the plant.
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Williams said the company reduced power to about 40 percent by 4 p.m. to reduce the need for feedwater by at least half so the pipe could be isolated and drained.
"I say 'mildly' radioactive because most of the radioactive impurities generally stay in the reactor or its separate cleanup system. You could sort of think of the plant like a distiller with the reactor producing very clean steam," he said in an e-mail late Thursday afternoon.
He said the water in the feedwater system produces "very clean steam," which is condensed and repressurized for reuse in the reactor.
Williams said the leak was discovered Thursday morning during a routine inspection by plant workers. He said he didn't know where the leak was — either it was coming from a faulty valve, like the other leak, or from a faulty weld or joint, or was a weakening in the wall of the piping.
Hofmann said Entergy held a briefing on the leak Thursday afternoon which was attended by Uldis Vanags, the state nuclear engineer.
"Some leaks can wait to be fixed while others such as this require immediate attention. Entergy is taking the proper action to address this leak. We will, however, be very interested in what Entergy finds is the cause," said Hofmann.
Robert Stannard, a Statehouse lobbyist for Citizens Awareness Network, an antinuclear group, said the two leaks in two days raised plenty of eyebrows at the Statehouse.
"This is the opening week of the Legislature and there's not one, but two leaks at this aged plant. Vermonters can expect to see more leaks and more problems," said Stannard. "Sometime there will be a leak that breaks the camel's back."
He said the continuing problems at the plant was undermining public and legislative confidence in the plant, which supplies one-third of all the electricity used in Vermont.
Vermont Yankee's original federal license expires in 2012, and Entergy Nuclear is seeking federal and state approval to operate for another 20 years. Entergy has preliminary approval from the Nuclear Regulatory Commission, and still needs the approval of the Legislature and the Public Service Board.