Nuclear leaks appear to turn corner

Posted
Sunday March 21, 2010

VERNON -- The main source of radioactive tritium leaking at the Vermont Yankee nuclear plant appears to have been stopped, and levels measured in a nearby monitoring well have been dropping for weeks. But plant, state and federal officials say the story is far from over.

A 30-foot-wide alley between two buildings at Vermont’s lone nuclear plant has been the focal point as engineers have used a high-pressure stream of water to dig around underground pipes and expose a concrete pipe tunnel. The result now is a trench, 15 to 17 feet deep and crowded with pipes.

The tool that produces that high-pressure water stream is called a hydro-excavator.

"Because of the sensitivity of buried pipes and not disrupting any of the pipes, some of which include fuel oil lines, air supply lines, delicate piping that’s underground," Vermont Yankee spokesman Larry Smith said as he leaned on a railing and gazed down into the hole.

"This hydro-excavator injects a slug of water, a slurry, and then vacuums up the dirt and that’s why it took so long for us to go down 15 feet," he said. "It’s meticulous, but that’s the only way you can excavate around buried or underground piping without doing any damage to them or disrupting anything else that might be underground."

Triple failure

Once the concrete pipe chase was exposed, engineers put a small robot equipped with a camera into it and soon found the triple failure believed to have lead to the leak first made public Jan. 7.

Among the pipes housed in the concrete enclosure were two connected to Vermont Yankee’s advanced off-gas building, where impurities are removed from steam so it can be condensed back to water and routed back for another trip through the reactor. The pipes were connected to two redundant systems, meant to back one another up. Both deteriorated during the plant’s 38-year life and leaked.

That should not have been a problem if the second failure had not occurred. There was a drain in the bottom of the concrete enclosure to catch just such leaks and send any liquid coming to it to be processed. Concrete dust from the enclosure’s construction or from a later retrofit mixed with water formed mud that plugged the drain, said William Irwin, the state radiological health chief.

The water then backed up and found a third flaw, a gap in the wall of the concrete enclosure around another pipe. And that’s where the water containing tritium, a suspected cancer causer when ingested in large amounts, escaped into groundwater.

"The systems failed," said Neil Sheehan, spokesman for the Nuclear Regulatory Commission’s Northeast regional office.

That sort of failure could have caused headaches and a public relations challenge for any nuclear plant. For Vermont Yankee, it was a nightmare.

The plant is trying to win a 20-year renewal on a 40-year operating license that expires in March of 2012, two years from now. Vermont is the only state with a law giving its Legislature a vote on nuclear relicensing; others leave it to utility regulators and the NRC. The tritium leak came as Gov. Jim Douglas was calling on lawmakers to give Vermont Yankee a green light for relicensing.

Worse, senior plant officials had told lawmakers and regulators -- the latter under oath -- that Vermont Yankee did not have the sort of underground piping that could carry tritium. Douglas called that a breach of trust, did an about-face and asked that lawmakers delay voting on the plant’s future until public trust could be restored.

The state Senate would not be deterred, crafting a bill to allow the Public Service Board to proceed with regulatory hearings on relicensing and then defeating it 26-4. The plant and its supporters are hoping for another vote -- with a different result -- next year.

Technicians at the plant, meanwhile, spent the winter scrambling to find and stop the leak. They dug 20 new monitoring wells and mapped an underground plume of contaminated water stretching from the plant’s main buildings to the nearby Connecticut River.

If the tritium investigation is entering the home stretch, plant officials aren’t saying so. Smith said a "stakeholders’ meeting" is planned at which plant and state officials will provide an overview of the situation to interested parties. Irwin said the session could occur within the next week or so; Smith would not be that specific.

By March of 2012, when Vermont Yankee either will be shutting down or will have turned its fortunes around and be ready for continued operation, the tritium leak of 2009-2012 should be "completely dissipated," Irwin said.


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