New radioisotope found at Yankee
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By Susan Smallheer STAFF WRITER - Published: February 26, 2010
VERNON – Entergy Nuclear has found traces of cesium-137, a radioisotope, about 15 feet underground in the excavation trench where it is searching for the leak that has contaminated groundwater at the Vermont Yankee reactor for the past two months.
Entergy Nuclear said the cesium was found in trace amounts, and at background levels, a result of radiation from nuclear bomb tests and the Chernobyl nuclear accident in 1986, and was not the result of the tritium leak.
Entergy wouldn't disclose the cesium measurements.
But William Irwin, radiological health chief for the Vermont Department of Health, said it was too soon to say what the source of the cesium was, but that testing in the next few days, along with the continuing excavation, could reveal the source.
"There are two reasons: First, all soils and sediments have trace amounts of cesium-137 from above-ground weapons tests and Chernobyl. Second, they are digging where they expect to find a leak of radioactive water," Irwin wrote in an e-mail.
"When other radionuclides are found, too, we will be sure," he said.
Arnie Gundersen, a nuclear expert working for the Vermont Legislature, said cesium-137 is a fission product when uranium splits. He said cesium would date back to fuel failures from the 1970s through the 1990s at Vermont Yankee.
"Nuclear fuel failures would have left cesium and strontium in the pipes in the off-gas system. When the pipes break, the fission products and activation products like cobalt-60 will come out into the soil," Gundersen said.
Meanwhile Thursday, the Nuclear Regulatory Commission said it was sending Don Jackson, a regional branch chief, to oversee Entergy efforts to search for the tritium leak, given that Entergy had put the head of its tritium task force on administrative leave.
John Dreyfuss, Entergy Nuclear's director of nuclear safety assurance, was put on administrative leave, along with three other Entergy employees, for his role in Entergy giving false information to state regulators about underground pipes containing radioactivity.
Neil Sheehan, a spokesman for the Nuclear Regulatory Commission, said Jackson was sent to Vernon to oversee the investigation, and he said Jackson would remain through next week, "ensuring plant operations remain safe amid all the key personnel changes."
Sheehan said other nuclear reactors have made significant managerial changes, noting that the Millstone plant in Connecticut did in the early 1990s.
Sheehan said John McCann, who came from Entergy Nuclear's Northeast office in White Plains, N.Y., was now the acting site vice president. Previously, Michael Colomb had been site vice president, but he was one of the employees Entergy Nuclear reprimanded earlier this week over his role in the underground pipe controversy.
Larry Smith, spokesman for Entergy Nuclear, said the cesium was found so far underground because the area being excavated is a filled-in area, and that the fill came from surface areas.
Irwin said the cesium-137 could come from the leak, but it would be expected to find cesium and other radionuclides close to the source of the leak.
Entergy Nuclear said Wednesday it believed it was getting close to the source of the leak, which has sent high concentrations of tritium into the groundwater, up to 2.6 million picocuries per liter, in one well. The federal EPA drinking water standard, for comparison, is 20,000 picocuries per liter.
Smith said he didn't have the cesium-137 measurements Thursday, but he said Entergy chemistry technicians had reported to him that the cesium came from the background tests.
Smith declined to talk about the management changes at Vermont Yankee.
According to the daily update from the Department of Health, tritium levels in the contaminated groundwater wells are declining, with the most contaminated well now at 1.79 million picocuries. The second most contaminated well measured at 892,000 picocuries, and the third at 552,000 picocuries.
Excavation of the pipe tunnel connected to the advanced off-gas system is proceeding by hand because of the delicate nature of the area, the health department noted.
A section of the dig site is being handled as a radiologically controlled area, Smith said, and radiological controls for workers are in place.
Leak testing of the pipe tunnel is slated for this weekend.
susan.smallheer@rutlandherald.com
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