Feb 23 - Brattleboro Reformer, Vt.



Excavation of a pipe tunnel suspected of being the source of a leak of tritiated water at Vermont Yankee nuclear power plant is back under way.

It had been on hold until Sunday night due to difficulties encountered last week with the off-gas system tunnel's concrete footing and boulders in the dirt around the tunnel.

As of noon on Monday, the excavation had reached seven feet deep. Another four feet of dirt was expected to be removed by the end of Monday. The dig needs to go 15 feet deep to expose the bottom of the pipe tunnel.

"As the excavation proceeds, shoring is being installed to hold back the dirt wall to prevent the possibility of a cave in," stated the Vermont Department of Health in its daily Yankee update .

 Once Entergy has finished excavating around the pipe tunnel, it will test for leakage paths to the ground from the tunnel floor using pure water, stated the DOH. This leak testing could begin as early as Wednesday, stated the DOH. Water used during the test will be collected and processed through plant systems.

An above-ground enclosure will be erected to provide weather protection for the excavation area and to control access to what will be a radiologically controlled area.

Meanwhile, water is continuing to show up in the pipe tunnel and is being collected in a sump and is being removed, stated the DOH.

Once the pipe tunnel has been tested, Entergy technicians will also inspect

the plant's hydrogen recombiner moisture separator drains.

"The (recombiner) piping is not actually visible from the excavation," stated the DOH. "Imaging technology, excavation under the (off-gas system), or additional wells may be needed to test whether this piping leaks."

Two new deep monitoring wells were installed and digging for two additional shallow groundwater monitoring wells continues, stated DOH. The information from these new wells will help engineers and hydrology experts better understand groundwater flows beneath the site.

Groundwater at Yankee wasn't being monitored for tritium until 2007, when wells were drilled in accordance with guidelines established by the Nuclear Energy Institute following tritium leaks at other nuclear power plants.

Two or three years before the plant started running in 1972, an environmental monitoring program was put in place. Until Jan. 6, there had been no indication that the plant, which has zero liquid effluents released to the environment, had been leaking.

"That's not a fact that is in evidence right now," said John White, the branch chief for reactor safety in Branch 1.

Right now the health danger to the general public is "essentially zero or very nearly a zero dose," said Steven Garry, an NRC health physicist.

"From a public health and safety perspective, we're in good shape," he said.

Nor has tritium been discovered in the Connecticut River, said Garry, though "It's logical to presume there is some small level of tritium in the river."

Bob Audette can be reached at raudette@reformer.com, or at 802-254-2311, ext. 273.

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