November 14, 2008
By Susan Smallheer Herald Staff
BRATTLEBORO — The discovery of more degraded wooden support beams in Vermont Yankee’s cooling towers — this time in the reactor’s only safety dedicated cell — raised questions Thursday about how thorough a special Nuclear Regulatory Commission inspection was this summer.
Workers at the Vermont Yankee nuclear plant had to immediately replace five deteriorated major support columns in the one safety-related cell of the reactor’s two cooling towers during the plant’s recent refueling outage, according to the NRC.
The degraded columns, which are about 40 feet tall, were discovered after Entergy Nuclear started its gradual overhaul of the two cooling towers, replacing the wood with fiberglass. The overhaul is expected to take a couple of years.
Entergy Nuclear spokesman Robert Williams said the columns were bowed and cracked. “All could have been deemed acceptable for continued service, but we conservatively chose to replace them rather than wait until the next refueling outage,” Williams wrote in an e-mail.
He noted that two 2-by-4-inch “transverse” timbers were also replaced.
The news of the compromised columns surprised the Department of Public Service, which said the safety cell of the west cooling tower had been inspected by the Nuclear Regulatory Commission this summer, after other problems developed in the east cooling tower.
“We are eager to hear the NRC’s explanation,” said Stephen Wark, spokesman for the department, noting that the NRC had sent a special team of inspectors to the Vermont reactor in July, after a large leak developed in the eastern tower because of a lack of adequate supports.
Neil Sheehan, spokesman for the NRC, declined to say exactly what was wrong with the wooden timbers, saying only they had to be replaced because of “aging.” But he said workers have been classifying all the wood in the cooling towers according to how quickly they should be replaced, giving each a grade of 1, 2 or 3. The timbers in question required immediate replacement, he said.
“Entergy replaced four or five columns as well as a number of diagonal braces. As for other timbers in the cell, they were categorized based on their condition. Some were determined to be in need of immediate replacement and they were changed out. Our senior resident inspector observed the work as timbers were being taken down and replaced,” Sheehan said.
“This will improve the structural integrity” of the cell, he said.
The cooling towers are currently not in service because of the cool weather and the cool temperature of the Connecticut River, which is used for cooling water by the reactor. Typically, the cooling towers are not in service from mid-October until mid-May.
Sheehan noted that the safety cell provided back-up cooling for the reactor in the event of a “catastrophic” event, such as the loss of cooling water from the Connecticut River.
Wark said that Uldis Vanags, the state nuclear engineer, had been informed by Entergy Nuclear about the problem, as well as the five panel members of the state’s special inspection team.
The cooling towers have become a persistent source of problems at the Vernon reactor, ever since the west cooling tower partially collapsed in spectacular fashion on Aug. 21, 2007. The plant sharply reduced power for weeks as it made emergency repairs. Problems cropped up twice this summer in the west cooling tower, also causing Entergy Nuclear to cut power production.
Contact Susan Smallheer at email@example.com.