New well has higher levels of tritium
BRATTLEBORO -- A water sample from one of three new wells drilled at Vermont Yankee nuclear power plant last week showed tritium levels more than twice as high as those found in a monitoring well in January.
The level in the new well, which is about 100 feet south of the well that first tested positive for tritium on Jan. 7, was 70,500 picocuries per liter, according to the Nuclear Regulatory Commission.
Another new well, about 200 feet south of the original well, also tested positive for tritium, at 1,800 picocuries per liter.
The new wells and the original well are located between the reactor building and the Connecticut River.
No elevated tritium levels have been found in the Connecticut River or in any drinking water well samples, according to the Vermont Department of Health.
The levels in the original well had been ranging between 17,000 and 28,000 picocuries. On Sunday, a new test showed the level had increased to 32,000 picocuries, just over the NRC's reporting limit of 30,000.
A second test showed the level had dropped to 28,400.
The purpose of the monitoring wells is to determine the tritium concentrations in the ground water to help find the source of the leak and to map out the area of contamination, stated Rob Williams, spokesman for Yankee, in an e-mail to the media.
"So we're on the right track," he stated.
Engineers are planning six more wells around the plant buildings, he wrote.
"These will serve as important additional data points as Entergy continues to outline the dimensions of the groundwater contamination plume and hone in on the source of the leakage," stated Neil Sheehan, spokesman for the NRC, in an e-mail to the media.
Sheehan said the level of tritium detected in the wells needs to be kept in perspective.
An individual would have to drink 2 liters of water per day at 20,000 for 365 days to receive a dose of 4 millirems in a year, he said. An individual receives about 360 millirems per year from natural sources such as radon and cosmic rays, and manmade sources, such as X-rays and cross-country flights.
At this time, there has been no report on whether there are other radioisotopes in the water samples taken from the new wells, according to the DOH, which is posting daily updates on the tritium investigation on its Web site.
In addition to digging the new wells, Entergy is also digging up the off-gas drain line to determine if it's the source of the leak.
The off-gas system extracts from steam radioactive noble gases, such as krypton and xenon, which are stored in a holding tank before being metered out through the plant's stack.
Preparations are also underway to give technicians access to the off-gas duct, which connects the exhaust from the reactor, radioactive waste, turbine and off-gas buildings to the stack.
It runs along the river just west of these buildings, and could be a possible source of tritium, according to the DOH.
Yankee is also performing a leak test on the pipe trench in the radioactive waste building to determine if it's the source of the leak. A new well drilled near the pipe trench has not tested positive for tritium, according to the DOH.
Bob Audette can be reached at firstname.lastname@example.org, or at 802-254-2311, ext. 273.
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