Vermont Yankee excavation continues, drinking water well taken out of service, decommissioning fund bolstered by $40 million

first_imgA statement from Vermont Yankee Monday night reported that excavation near underground piping thought to be the source of a tritium leak was making progress; it also said that a drinking water well in the general area of the test wells that have showed elevated levels of the radioactive isotope will be taken out of service as a precaution, even though it is well beneath the test wells and has not shown in testing to contain tritium; and that a “parent guarantee” of $40 million from Entergy to the Vermont Yankee decommissioning fund has been approved by the Nuclear Regulatory Commission.The statement said that good progress was made this past weekend in Yankee’s effort to excavate and expose the Advanced Off Gas concrete pipe tunnel for inspection. Excavation in the AOG area is now down to 11 feet and shoring is in place. Soil samples taken during excavation have not shown any signs radioactivity in the soil.  As expected, at the 11 foot level, radiation being emitted from nearby piping has made a section of the dig site a radiological controlled area and all radiological controls for workers entering this area of the excavation are in place. Additional cross bracing is being welded in place to support the shoring side panels. When completed, excavation and shoring will resume to 15 feet. An engineered solution to capture potential leakage encountered at the unearthed AOG tunnel has also been prepared if it is needed. The enclosure above the excavation area is in progress and will be completed after final parts of the shoring are moved into place and excavation has reached 15 feet.Plans continue to test for leakage paths to the ground from the Advanced Off Gas concrete pipe tunnel floor using pure de-mineralized water; engineers are considering the use of environmentally benign dyes for the water to assist in leakage checking. This will help determine if and where the tunnel theoretically may be leaking water into the ground. This test will be performed after excavation exposes the tunnel floor and mitigation catch basins are installed under the tunnel allowing technicians to observe any leakage paths. Pure de-mineralized water used during the test will be collected and processed through plant systems.Tritium concentration monitoring is ongoing. The installation of the two new deep monitoring wells is complete and they are in the process of being developed (GZ-13D and GZ-14D). Digging for two additional shallow groundwater monitoring wells continues. One well, GZ-16 has encountered some interferences and a new location is being determined for the well. The information from these new wells will help engineers and hydrology experts better understand groundwater flows beneath the site.The Construction Office Building (COB) drinking well, one of several wells that supplies drinking water to the VY site only, is set in bedrock deep below the flow of the surface groundwater containing tritium above it. The COB well is over 350 feet below the surface into bedrock while the groundwater monitoring wells are on the order of 25 feet to 35 feet deep and are above the bedrock. While daily testing of the well has consistently shown all sampling results to be below detectable limits, the deep well is within the field of shallow groundwater wells that have tested positively for tritium. In addition, there is a small possibility that continued use of the well could result in its cross contamination. Therefore, as a prudent precaution, the decision has been made to take the COB drinking water well out of service. The well will, however, be maintained as a deep monitoring well and will be included as one of the deep wells that will be part of geophysical testing to determine the characteristics of the bedrock. Design changes and temporary modifications are being developed so that drinking water to the COB can be supplied by another well onsite. The switchover is expected to occur later this week after obtaining approval from the Agency of Natural Resources. While this investigation continues, it is important to note that there has been no tritium levels found in any samples taken from drinking water wells or the river.Decommissioning Fund Update.  As previously reported, due to the recent economic downturn, VY’s decommissioning trust fund was determined to be “low” by the NRC last year. We committed to bridge the difference with a Parent Guarantee from Entergy, for $40 million dollars by end of 2009. Vermont Yankee recently received a letter from the NRC that acknowledges that its Parent Guarantee is satisfactory and in place, and the decommissioning funding now meets NRC regulations.For more details on the tritium investigation, the Vermont Department of Health has a thorough status report on the investigation at this web link: is external)Also helpful is the Nuclear Regulatory Commission web page on tritium monitoring:…(link is external)Source: Vermont Yankee. 2.22.2010last_img read more