VERNON — Routine tests at the Vermont Yankee nuclear power plant have detected Strontium-90 (Sr-90) in monitoring wells at the site.
The Vermont Department of Health (VDH) states that the levels of the radioactive isotope are low enough that they pose no immediate risk to people's health.
The VDH announced the findings on its website on Feb. 9.
Routine tests of water samples in August 2014 from groundwater monitoring wells at VY turned up the Sr-90. According to the VDH, the tests were part of the department's environmental radiological surveillance program.
The Sr-90 was found in wells GZ-3, GZ-13, GZ-16, and GZ-18, five of 31 monitoring wells in VY's environmental monitoring program.
“This is the first time Sr-90 has been found in groundwater at Vermont Yankee,” wrote the Vermont Department of Health in a press release. “The water is not available for consumption, the levels detected are well below the EPA's safe drinking water threshold, and there is no immediate risk to health.”
A few years ago, detection of tritium in the monitoring wells helped uncover a leak at the plant. In 2010, environmental testing showed Sr-90 in soil collected near the source of the tritium leak.
Other samples of Sr-90 found in fish in the Connecticut River and in rivers elsewhere in Vermont have remained consistent with background levels of Sr-90 found globally, said the VDH.
Sr-90 is a byproduct of nuclear reactors and nuclear weapons. It is found worldwide and has a half-life of 29 years. At high concentrations, the radionuclide has been linked to bone cancer, cancer of soft tissue near the bone, and leukemia.
The state sent 21 water samples to its contract laboratory which, under a new agreement with the state, tests for “hard-to-detect” radionuclides like Sr-90.
The laboratory reported to the state on Nov. 25, 2014 that four of seven samples contained Sr-90 above the lower levels of detection but below the Environmental Protection Agency's safe drinking water level.
“Although the specific source of the Sr-90 is unclear, it is likely that Sr-90 in groundwater and soils at Entergy [Nuclear] Vermont Yankee are the result of past leaks and fallout from air releases at the station during its years of operation,” wrote the VDH in a press release.
Nuclear Regulatory Commission (NRC) spokesperson Neil Sheehan said most of the samples were around 2 picocuries per liter (pCi/L). The highest concentration of Sr-90, according to the VDH, was 3.5 pCi/L. The EPA's safe drinking water level is 8 pCi/L.
The water samples have been examined by the state's contracted lab and Entergy's independent lab. Oak Ridge National Laboratory also reviewed samples from the monitoring wells independently, at the state's request.
The federal lab confirmed the state's findings on Jan. 29.
VY spokesperson Martin Cohn said that Entergy's lab did not find any Sr-90 because the levels in the samples were lower than what the lab tests for or what the NRC requires that it test for.
Entergy received news of the test results in November, said Cohn. In response, the company retested the August samples and proceeded with its quarterly sample gathering scheduled for November.
The NRC requires that Entergy continue monitoring the groundwater wells for as long as it holds the plant's license.
Cohn said that there will always be a groundwater monitoring program in the decades of decommissioning to come, though the program's details and specifications might change.
VY and Entergy meet all of the NRC's requirements for testing, said Cohn, noting that Entergy sees no reason to change its monitoring program in response to the state and Oak Ridge finding Sr-90.
Sheehan said the NRC still has questions about the labs' findings.
“It's a fairly limited data set,” said Sheehan. “At this point there are four samples.”
Sheehan said that at this point, the samples point to residual contamination from an old leak rather than a new issue at the plant.
If it is from a new leak, the tests should also show tritium, which moves through the environment more quickly than Sr-90 and has a shorter half-life, he said.
Two of the wells that showed Sr-90 were located near the tritium plume from a previous leak. Two other wells, however, were north and south of the plant site respectively, said Sheehan, noting the NRC wants to explore these fundings further.
The NRC suspects the test from these wells are false positives, said Sheehan.
“There's just no physical way Strontium-90 can migrate five miles north - upstream,” said Sheehan.
Same for the well south of the plant, he said: There is no evident physical pathway for the isotope to travel.
In the short term, the NRC doesn't see any cause for alarm, said Sheehan. It will expect Entergy to include the findings from August 2014 in its decommissioning file and address them during the process.
In the long term, continued Sheehan, the finding of Sr-90 on the VY site could mean Entergy will have more site decommissioning on its hands as it works to decontaminate the site and prepare it for unrestricted use.
The NRC requires that radiation exposure at a released plant site not exceed 25 millirem a year.
David Lochbaum, director of the nuclear safety project for the Union of Concerned Scientists, said the Sr-90 finding came with some good news: the nuclear industry conducts more monitoring so it catches potential dangers sooner.
The levels are also very low, he said.
Since 2006, the industry has stepped up the number of monitoring wells at plant sites, he said. More monitoring means it's more likely a plant will discover a leak.
“Because of monitoring now, the nasty surprises are less likely,” said Lochbaum.
This also means that more testing means more issues are discovered, he said.
The potentially bad news, he said, is that the Sr-90 “could be a new leak.”
“It can't be ruled out,” Lochbaum said.
He added, however, that it's likely the Sr-90 signals an old leak rather than a fresh one.
Initial testing in 2009 and 2010 turned up tritium from the leak at the plant, he said. Tritium is usually the first sign of a leak because it moves so quickly; its presence often indicates that other contamination will follow.
People should expect to find Sr-90 after a leak, he said. “It's more surprising not to discover the whole posse then only find the lead horse.”
In regard to the two respective wells where the isotope was detected north and south of the plant, Lochbaum said those results might not be false positives. The Sr-90 might have come from fallout from above-ground testing of nuclear weapons in the 1960s, he said, or it could have also been released from VY into the atmosphere through the plant's tall stack.
Tests can't distinguish the radionuclide's source, he said.
The VDH and Entergy will continue their radiological surveillance programs throughout VY's decommissioning.