Nuke plant still at 25 percent power after mishap

The Nuclear Regulatory Commission is sending experts to begin an investigation Monday into circumstances surrounding a leak in one of the cooling towers at the Vermont Yankee nuclear power plant and to verify that it is safe to continue operations.

NRC Executive Director for Operations Bill Borchardt is also traveling to the plant to consult with the inspectors and plant officials Monday and report back to Chairman Dale Klein and other members of the commission, according to a statement released Sunday.

Vermont Yankee nuclear plant remained at only 25 percent power Sunday in the wake of discovery of problems in cooling towers and continued low flow of the Connecticut River, which it draws water from.

On Friday, the plant's operators reported a leak in a pipe in one of its cooling towers, and said later that investigation revealed problems in the other tower -- broken or degraded pipe brackets on five so-called "saddles" that support the main pipe that brings river water to the top of the tower.

The nuclear plant has two cooling towers, each consisting of eleven cells. Only one cell in the west unit is considered to be safety-related.

"While Friday's leak was not in the one cooling cell considered safety-related, we know there is significant public interest in this event. We need to independently verify that the safety-related cell is structurally sound," Samuel J. Collins, an NRC regional administrator, said in the statement.

"It appears that that broken or degraded bracket was not due to decay but appears to be related to stresses in the design of the new interface between the bracket and the previously replaced column in that area," said spokesman Rob Williams.

Both towers remained out of service Sunday. As a result, power -- which had been reduced to 47 percent after Friday night's incident -- had to be reduced further Saturday because of low river flow, so that Vermont Yankee stayed within the limits of its river water temperature discharge permit, Williams said.

Last August, a cooling tower cell collapsed in a shower of wood, water and debris.

Plant owner Entergy informed the NRC that Friday's leak "occurred when the supply header, which carries 90,000 gallons per minute of water, sagged after the underlying horizontal support beam broke away from the vertical column to which it was bolted," the NRC said in the statement.

"Minor cracks were also found to supporting members on two of the west cooling tower cells, including one that sustained a pipe break and partial collapse last August," according to the statement.

Williams said Sunday it was unknown how long it would be before repairs were accomplished and the plant restored to full power.

(Source: The Boston Globe)