As the extraction well pumping continues, Vermont Yankee technicians continue to sample for tritium via the monitoring wells. According to Vermont Yankee, a recent positive reading for tritium in one of the deep (70 feet) overburden wells was mischaracterized in news reports as a new source of tritium. It is not. The groundwater monitoring data shows that the flow of groundwater is east/northeast with a slight downward gradient. With the leakage stopped, the down-gradient soils and well readings had not reached an equilibrium. Therefore, slightly elevated levels to the east/northeast are due to the residual tritiated groundwater flow in that direction. Since the leakage was stopped, the monitoring wells near plant equipment show a definite downward trend in tritium concentration. The overall flow gradient in the bedrock is upward and there has been no tritium detected in any drinking water wells or in the river.
Contrary to a headline in a local newspaper and several media reports, Entergy Vermont Yankee has not organized nor is Entergy participating in a closed, tritium-related meeting on April 14 between the Nuclear Regulatory Commission and state officials from Vermont, New Hampshire and Massachusetts.
The pumping of groundwater from the extraction well continues and preparations are underway to drill another extraction well to increase the flow rate into surface containers. The water will be processed and made ready for re-use in the plant.
In information provided by the Vermont Department of Health and available on its Web site, another finding of interest at the excavation site is cesium-137. This radioactive material is called a fission product. It does not exist naturally. It is only produced as a result of nuclear reactions, primarily from nuclear reactor fuel fissioning, from major nuclear reactor accidents including Chernobyl in 1986, or from nuclear weapons fallout. Cs-137 is commonly found in soils, sediment and some vegetation. Concentrations are usually around 100 picocuries per kilogram (pCi/kg), and Cs-137 is usually only found at the earth's surface, not deep underground. Given the Cs-137 in these soil samples have been found 15 feet below the ground surface, it is assumed the Cs-137 comes from the Vermont Yankee leakage. Given also that the concentration of Cs-137 in the soil samples are three to 12 times the concentration expected from Chernobyl or nuclear weapons fallout, it again appears likely the Cs-137 comes from Vermont Yankee reactor related sources. The same is true of strontium-90 (Sr-90), which has not yet been detected in any soils, sediment or water.
However, Vermont Yankee officials have said that water from the systems that leaked into the AOG pipe tunnel are not contaminated with Cs-137. They have said that Vermont Yankee reactor process water and condensate have not indicated Cs-137 content for many years, not since the plant had minor fuel rod leakage in the late 1970s and early 1980s when many plants had similar problems with "pin-hole" leaks in fuel rods. Given these points, it may be that the Cs-137 found in the soil samples came from surface contamination within the AOG pipe tunnel. This surface contamination may have been washed from the AOG pipe tunnel walls, floor and piping surfaces by the leaking steam and water from the damaged AOG hydrogen recombiner steam trap drain lines.
The Health Department has asked Vermont Yankee to sample and analyze the debris in the AOG pipe tunnel to see if it contains Cs-137, and to provide samples to the Health Department for independent confirmation.
Regardless of the questions raised by the Cs-137 findings, these soil samples confirm that this was an area of significant leakage of contaminated water into the environment. The samples also provide important information about the extent of contamination in the soil. In particular, they show that radioactive metals Mn-54, Co-60, Zn-65 and Cs-137 appear to have migrated at least four feet from the leakage pathway in the soil. These soils may be remediated by Vermont Yankee by excavation and disposal as radioactive waste. Water sample results, for example from groundwater monitoring wells GZ-10 and GZ-15, indicate the metals have not migrated 10 to 20 feet from the leakage pathway point of entry into the soil. The Department of Health will continue to analyze all samples for these radioactive metals and hard-to-detect radioactive materials like strontium-90, another fission product.
Source: Entergy Vermont Yankee. Vermont Department of Health. March 30, 2010.