Radioactive tritium level spikes in Yankee test well
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In this photo taken June 9, 2009, a warning sign is seen at the Vermont Yankee nuclear power plant in Vernon, Vt. The discovery of radioactive tritium at a Vermont nuclear plant brings to at least 28 the number of tainted U.S. reactors. That means more than a fourth of all reactors in the United States have tritium leaks. (AP Photo/Toby Talbot) AP |
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By SUSAN SMALLHEER Rutland Herald Staff - Published: February 2, 2010
VERNON – Significantly higher levels of tritium have been discovered in one of the new monitoring wells drilled at Vermont Yankee nuclear reactor to help locate a radioactive leak, the Nuclear Regulatory Commission said Monday.
And the levels of tritium rose from 70,500 picocuries per liter on Sunday to 75,300 on Monday, a development that Entergy Nuclear officials said was to be expected. That level is close to four times the federal standard for drinking water of 20,000 picocuries per liter.
Two of the three new monitoring wells drilled last week have now tested positive for tritium, with the second one showing relatively low levels. Federal officials insist the levels are not a threat to human health.
One well, GZ-14, located about 75 feet from the first contaminated monitoring well, tested positive for 70,500 picocuries per liter of water in a sample taken Sunday. But that reading jumped about 5,000 picocuries in one day, as Monday's test results registered 75,300 picocuries, according to Neil Sheehan, a spokesman for the Nuclear Regulatory Commission.
While the federal drinking water limit for tritium is 20,000 picocuries per liter, the reportable standard set by the NRC is 30,000 picocuries.
A third well, GZ-4, also tested positive for tritium, both Entergy Nuclear and the NRC reported, but the levels were much lower, at 1,840 picocuries per liter That well is 100 feet further south down the Connecticut River bank.
For comparison, the first well that revealed the radioactive leak, tested 32,000 picocuries on Saturday.
The groundwater monitoring wells are generally shallow, in Yankee's case 25 to 30 feet deep, while drinking wells are usually in bedrock, hundreds of feet deep.
As they have said since the tritium problem first surfaced on Jan. 7, Entergy and the Nuclear Regulatory Commission said the new tritium levels, while double the NRC's reportable levels of 30,000 picocuries, posed no threat to the general public.
Sheehan said even though the federal reportable level set by the NRC was 30,000 picocuries, the levels in the new well still weren't a threat to safety.
He said an individual would have to drink two liters of water per day, with a concentration of 20,000 picocuries, for 365 days to receive a dose of 4 millirems in a year.
He said to keep that in context, the average person receives about 360 millirems per year from natural sources, such as radon and cosmic rays, or manmade, such as X-rays, airline travel and radiation.
Sheehan said that the new well statistics were "important additional data points" for the Entergy staff working to find the source of the radioactivity.
Arnie Gundersen, a nuclear engineer who is a member of the Vermont Oversight Panel and a consultant to the Legislature on nuclear issues, said that he expected the radioactive plume would only increase.
"Even after the leak is found, the plume will continue to grow and likely the concentration will go up before it goes down," said Gundersen.
The new test results will help hydrologists and engineers working to locate the source of the tritium at Vermont Yankee, said Robert Williams, spokesman for Entergy Nuclear.
"The purpose of the monitoring wells is to characterize the tritium concentrations in the groundwater to aid in the investigation, so we're on the right track," said Williams.
Williams said that so far only three new monitoring wells have been put in place. He said the additional six wells would be drilled in the next couple of weeks.
He said the well contractors have to be very careful drilling in the Vermont Yankee compound, particularly since most of the wells are very close to the reactor building and other components buildings in the complex.
Williams said that while the new monitoring well showed increasing levels of tritium, no drinking water wells in the area had yet to register any tritium.
Entergy Nuclear has several drinking water wells on its Vernon property. Williams said he wasn't sure which of the wells supplied drinking water to the plant and its hundreds of employees. Not all of Vermont Yankee 650 employees work in Vernon since the company's corporate headquarters is in North Brattleboro.
According to the Vermont Department of Health's daily update on the tritium situation, the much higher tritium levels were expected.
"These positive results help define the length and breadth of the tritium plume on-site at Vermont Yankee," it stated.
Work continues on three major areas at a potential source of the leak or leaks: the advanced off-gas drain line, the radwaste trench, and the HVAC stack, serving heating, ventilation and air conditioning. That 78-inch diameter duct connects the exhaust from the reactor, rad waste, turbine and advanced off-gas buildings.
The health department's Web site said preparations to examine the ventilation system will take many days to allow access for inspection.
susan.smallheer@rutlandherald.com
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