The source of a tritium leak at Entergy’s Vermont Yankee plant has been identified, however the future of the reactor looks uncertain after the Senate decided to block a 20-year license extension for the unit.

On Wednesday, the Senate voted 26 to 4 to block a license extension for the Vermont Yankee plant, in light of the tritium leaks, inaccurate testimony by plant officials and uncertainty about the future cost of electricity in the state. Vermont is the only US state where the legislature has to authorize the license renewal in addition to the Nuclear Regulatory Commission.

The vote may not be final, but if it is, it will be the first time in 20 years that the public or its representatives have decided to close a nuclear plant in the USA. Vermont lawmakers could vote on the issue again next year. Entergy could also seek to override the decision and has said that the effort to win a 20-year license renewal is “far from over.”

Tritium Leak

Meanwhile, at the weekend, the source of the Vermont Yankee tritium leak, discovered in January, was verified as the point where the Advanced Off-Gas (AOG) pipe tunnel meets the 2-inch drain line.

The Vermont Department of Health said that taken together with other findings, results of the leak test and soil tests is good evidence that a crack revealed by excavation at the AOG pipe tunnel represented a significant pathway for radioactive water from the AOG pipe tunnel into the environment.

This pathway likely allowed nuclear steam that condensed into standing water on the floor of the pipe tunnel, while the floor drain was clogged, to leak into the environment. The radioactive water then likely contaminated the soil nearby with radioactive solids, and the groundwater nearby with tritium.

Boroscopic examination of the inside of the Advanced Off-Gas (AOG) pipe tunnel conducted on 28 revealed February no observable defects in the AOG drain line itself. The 2-inch carbon steel pipe appears to be intact from where it connects to the 12-inch diameter AOG pipe tunnel to the concrete duct that surrounds the drain line until the drain line reaches the AOG drain pit, according to Department of Health reports. An inch-by-inch inspection of the entire length of the concrete duct that surrounds the drain line is in progress. The boroscopic inspection shows there is enough space between the concrete duct and the PVC sleeve around the drain line to allow water to leave the pipe tunnel and enter the soil and groundwater outside the tunnel.

Excavation also revealed that, at the point where the drain line reaches the pipe tunnel, the concrete wall of the tunnel had been cut away, and concrete blocks were mortared into place. Workers are planning to remove some of these concrete blocks to place a robot in the tunnel. The robot will carry a video camera to allow better observation of the tunnel interior. This is important because there is some source of contaminated water still leaking into the tunnel. This water runs through the floor drain into the AOG drain pit sump, where it is pumped to the Radwaste Building for reprocessing. So far, the path for this water into the environment is not evident and investigations continue.

Other integrity tests of the pipe tunnel and the rest of the AOG drain line will have to be made to confirm that there are no other paths to the environment. New wells are being drilled and will be ready to begin sampling soon.

So far, all Vermont Department of Health and Vermont Yankee on-site and off-site drinking water well samples continue to show no tritium in excess of the lower limit of detection set by the EPA (20,000 picocuries per liter for tritium in drinking water).

A recent survey by conducted by Opinion Research Corporation has found that two thirds of Vermont residents are more likely to support 2012 closure of the reactor in light of the reports on the tritium leaks..

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