A May 14, 2010 radiochemical analysis of soil samples taken on March 17 from the Advanced Off-Gas (AOG) pipe tunnel excavation shows the presence of strontium-90 (Sr-90). Vermont Yankee shared these results with the Vermont Department of Health on May 20.
Sr-90 is a metal by-product of the fission of uranium in nuclear reactors, and is found in waste from nuclear reactors. The finding of Sr-90 in this area may be the result of fuel failures that occurred at Vermont Yankee in the 1970s.
Sr-90 is considered one of the more hazardous constituents of nuclear wastes because it is a very strong beta radiation emitter, with a long half-life (29.1 years). This means it takes a long time to decay naturally. If Sr-90 gets into the body (by inhaling contaminated dust or ingesting contaminated soil or water), it behaves chemically much like calcium, concentrating in the bones and teeth. Sr-90 differs from the other radioactive solids found in the soils at Vermont Yankee in that it is more soluble than those other materials. The more soluble a material is, the more likely it is to travel with groundwater.
The Vermont Department of Health, as well as Entergy-Vermont Yankee, is monitoring the environment for Sr-90 to verify that it is not found in groundwater, drinking water, river water or fish. A ground water sample from well GZ-10 immediately adjacent to the soils taken on February 8 whenthe well was measuring 2.5 M picocuries per liter of tritium was negative for Sr-90.
Sr-90 has been found only in soils so far, and only in soils near the point of origin for leakage from specific plant systems near specific plant structures. This radionuclide and all others found to have leaked from the plant have not to date been measured in any drinking water, river water or fish. Only tritium has been found in ground water.
Measuring Sr-90
Tritium from the nuclear reactor water that leaked from the AOG pipe tunnel through the ground water, flowing east into the Connecticut River, has been measured in ground water monitoring wells at the site. In addition, other radioactive materials in particulate form have been filtered by the soils near the AOG pipe tunnel. These include the metals cobalt-60, cesium-137, manganese-54, and zinc-65. Tritium and these particulate radioactive materials can be measured with instruments at the Entergy-Vermont Yankee on-site environmental laboratory, and at the Vermont Department of Health Laboratory.
Sr-90 is called a hard to detect radioactive material because special laboratory techniques must be used to separate the soft metal for analysis. Laboratories that practice these techniques are relatively few in number. The preliminary results of the hard to detect analysis performed by Vermont Yankee s contract laboratory, Teledyne Brown Engineering indicate Sr-90 concentrations from 152 to 8,290 picocuries per kilogram. The highest concentrations were found closer to the point of origin, and lower concentrations were found further from the point of origin. This indicates that the soil may be filtering the Sr-90 as well as it did the other particulates.
The Sr-90 data was reported along with other radiochemical analysis data for tritium and gamma radiation-emitting materials, including cobalt-60, cesium-137, manganese-54 and zinc-65. The measurements from Teledyne Brown are generally consistent with measurements from the same sample locations made by Entergy-Vermont Yankee s on-site environmental laboratory, and by the Vermont Department of Health Laboratory.
Diagram of the Soil Sampling Sites
A diagram of the soil study area shows sites where soil samples taken on March 17 have shown concentrations of Sr-90:
Site #1 is where the AOG drain line enters the AOG pit for drainage into the AOG drain tank.
Site #2 is at the elbow where the AOG drain line goes from a north-south direction to direct flow east a few feet to the AOG pit.
Site #7 is where the AOG drain line connects to the AOG lines in the AOG pipe tunnel.
Diagram:
http://www.healthvermont.gov/enviro/rad/yankee/documents
/VY_tritium_soil_sampling_sites.pdf
Soil Sampling Laboratory Test Result Graphs
The graph of preliminary results of Sr-90 shows that the highest concentrations are found closest to the AOG drain tank. This is only a few feet away from GZ-10, the ground water monitoring well that has registered the highest tritium concentration levels, around 2.5 million picocuries per liter (pCi/L). This means that Sr-90 analysis of ground water sampled from this well will give a good indication of whether any Sr-90 may have been taken up into ground water. So far, results are negative.
The graph also shows that at sites #1, #2 and #7, the concentrations of Sr-90 decrease as the contaminated water moved deeper into the soils. Soil samples taken the week of May 9 are now being analyzed. These samples were taken at greater depths than the March samples. If this trend holds true, the May samples, which the Vermont Department of Health Laboratory will analyze separately, should show lower concentrations of Sr-90.
Graph:
http://www.healthvermont.gov/enviro/rad/yankee/documents/
VY_Tritium_Data_Lab_AOGsoilsamples.pdf
Webpage:
http://healthvermont.gov/enviro/rad/yankee/laboratory_testing.aspx
NRC Ground Water Monitoring Inspection Report
Also on May 20, the U.S. Nuclear Regulatory Commission (NRC) released its Vermont Yankee Nuclear Power Station Ground Water Monitoring Inspection Report(exit VDH), detailing its findings regarding Vermont Yankee s implementation of the Nuclear Energy Institute s (NEI) Groundwater Protection Initiative and investigation to find and remediate the tritium leak.
The NRC identified no findings of significance and stated that Entergy-Vermont Yankee had not violated any NRC requirements. The NRC did, however, state that there were elements of the NEI Groundwater Protection Initiative that Entergy-Vermont Yankee had not completed within the specified time frame.
In particular, Vermont Yankee had not yet implemented a formal site-specific ground water monitoring program, had not incorporated site-specific hydrogeological information identified in a 2007 assessment, and had not updated its risk assessment and leak detection program for plant structures, systems and components. The last element includes enhancements in leak detection methods, spill prevention, barriers to leakage reaching groundwater, preventive maintenance, and frequent reviews of vulnerable structures, systems and components all to have been implemented by August 2008.
The report reviews the timetable of events and actions to investigate the source of tritium leakage and to remediate the contaminated groundwater, contaminated soils and damaged structures, systems and components involved in this leak.
The report also includes an estimation of the plume size an approximate triangle with a length from its point of origin of about 400 feet, a base about 300 feet wide at the edge of the Connecticut River, and a depth that varies from 5 to 9 feet. This yields an estimated volume of between 600,000 and 1,080,000 cubic feet. In addition, a total release of about 2.8 curies is estimated. 2.8 curies is equal to 2,800,000,000,000 picocuries.
The NRC concurred with Entergy-Vermont Yankee s estimate of off-site dose from the tritium contamination estimated to be between 0.00026 and 0.00035 millirem. To put this in perspective, 20,000 picocuries per liter of tritium in drinking water is generally equated to a dose of 4 millirem, so this is a very small dose.
Given the content of the inspection report, the Vermont Department of Health has asked both Entergy-Vermont Yankee and the NRC a number of follow-up questions, which we expect to be answered in the upcoming week. These questions generally seek opinions from the NRC about:
How Vermont Yankee can identify any new leaks from buried piping, when wells that might identify these leaks are sampling from a volume of the groundwater already contaminated with high concentrations of tritium
Whether the Construction Office Building (COB) well should be used again, but only to test for contamination in drinking water sources near the centerline of the tritium plume
Whether Vermont Yankee is monitoring buried underground piping and the condensate storage tank often enough to ensure that ground water is protected
We are also requesting from Entergy-Vermont Yankee a specific condition report from February 2010, the pending root cause analysis when completed, an updated hydrogeological report from Vermont Yankee s contractor, and an updated dose assessment using Vermont Yankee s off-site dose calculation manual.
Refueling Outage Ends
Vermont Yankee reports that it is closing out its remaining refueling outage activities and planning to begin start-up Saturday May 22. The AOG systems that were remediated to prevent further leakage from these systems into the environment are being warmed up for the start-up.
Source: Vermont Health Department. 5.21.2010