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January 29, 2010

VT Yankee: Closing in on Source of Tritium Leak?

VT-Yankee-10x22-crop-w Vermont Yankee continues to focus on a key underground pipe that carries steam away from the nuclear power plant's turbines to its main reactor stacks as a possible source of a tritium leak.

However, Vermont's top radiological health officer, Bill Irwin, told Seven Days that it is too soon to determine if this was the underground pipe leaking tritium into nearby groundwater.

The main focus of investigation and excavation is a pipe about 12 feet below the surface, said Irwin, called the advance off-gas system.

"It's very early on, but as a tritium source the drain line related to this off-gas system has been identified early on as a possible source, and excavation started a couple of days ago," Irwin told Seven Days via phone from the Vernon-based power plant.

Yesterday, around 4 p.m., workers encountered steam coming from the area of the pipe and halted work to further determine what steps should be taken, said Irwin. Samples from the ground did not prove to have tritium at high enough concentrations, but further digging will occur.

"Plant officials had hoped it would be indicative of a leak, but a sample taken last night and reported today proved they need to go deeper before they can confirm whether this is the source," said Irwin. He cautioned that finding the true source of the leak could be weeks, even months, away.

Part of the reason is the need to dig carefully while the plant is in operation.

"It brings a whole new meaning to the term 'dig safe,'" noted Irwin.

Vermont Yankee's owners are also looking at an area connected to the off-gas ventilation system, one that can be accessed without digging underground.

Arnie Gundersen, a nuclear engineer hired by the Legislature to keep tabs on Vermont Yankee, warned state officials in August that underground pipes carrying radionuclides — including the off-gas system pipe they are now investigating — existed. State officials brushed aside Gundersen's claims and allowed Entergy to reply to his concerns. The company said no such pipes existed.

Entergy made that statement to a legislative oversight panel, then repeated it to a state contractor and the Public Service Board.

This week, the governor called for the legislature to take a "time out" and not vote on Vermont Yankee's future this session.

Also, the Vermont Public Service Board put Entergy on notice that it wanted the firm to correct the statements made to the board regarding the existence of underground pipes at the plant. Attorney General Bill Sorrell is investigating whether Entergy officials should be held accountable.

The Senate Finance Committee will be taking testimony on Entergy’s power purchase proposal beginning next week, and the legislature will receive the Public Oversight’s Panel’s updated report on the reliability of the plant on February 16.

Here is the full Health Department report from this morning. The department will post its update this afternoon here:

Excavation late yesterday directed toward the AOG drain line resulted in the identification of what observers first thought to be a release of steam that could lead to the origin of tritiated water found in well GZ-3. Excavation was immediately stopped. Further investigation, however, could not confirm this as a steam release or leak.

Water samples extracted from the surrounding area (resulting from the hydroexcavation process and surrounding soil) were tested on site by Vermont Yankee. Results were not indicative of a leak. Tritium levels were found to be less than the Lower Limit of Detection of 600 to 650 picocuries/liter and trace amounts of other radioisotopes consistent with 1993 site soil characterization were also identified. There was not enough water found to allow for a “split” sample to be taken for independent testing by the Vermont Department of Health laboratory.

Because this was not definitively identified to be the source of tritiated water, excavation will resume today to reach the concrete pipe duct that contains the drain line and obtain additional samples for testing. Plant officials, in consultation with the contractors doing the excavation work, are determining the best way to reach the drain line, which lies at a depth of about 12 feet below the ground surface.

The investigation continues. We expect to post an afternoon update.

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