A Note from Larry Smith at Vermont Yankee

February 23, 2010

Vermont Yankee engineers and technicians continue their investigation into the source of tritium in the plant's groundwater.

Progress continues in our effort to excavate and expose the Advanced Off Gas concrete pipe tunnel for inspection. As mentioned in the last update, yesterday's work focused on additional cross bracing being welded in place to support the shoring side panels. That work was completed over night and into the morning and excavation resumed this afternoon. Soil samples will continue to be taken during the excavation process as we go down to the 15 foot level. To date, samples taken during excavation are consistent with prior site characterization studies and do not show signs of process piping leakage. As expected, at the 11 foot level, radiation levels rose slightly due to nearing underground process lines. Radiation control technicians 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. 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 are complete 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 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, GZ-16 and GZ-19, have encountered some interferences, delaying the installation of these wells. A new shallow monitoring well, to be located just west of the excavation site in the maintenance shop, will commence later this week. On Friday, down hole geo-physics testing of six monitoring wells will begin. The purpose of this testing is to determine the structure of the bedrock. Geo-physics testing takes several days to complete. The information from the new wells and geo-physics testing will help engineers and hydrology experts better understand groundwater flows beneath the site.

As mentioned yesterday, as a prudent precaution, the decision has been made to take the Construction Office Building (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 geo-physics testing. Design changes and temporary modifications have been approved, with concurrence from the Agency of Natural Resources, so that drinking water to the COB can be supplied by another well onsite. Preliminary work for the switchover is in progress, with completion in a few days. The Construction Office Building (COB) drinking well, which supplied 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' below the surface into bedrock while the groundwater monitoring wells are on the order of 25' to 35' 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.

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.

Also today, Entergy sent a response Letter to Commissioner O'Brien regarding an allegation by an unnamed employee about a possible tritium leak in 2005. A copy of the letter is provided in this e-mail. Read More.

For more details on the tritium investigation, the Vermont Department of Health has a thorough status report on the investigation at this web link: http://healthvermont.gov/enviro/rad/yankee/tritium.aspx

Also helpful is the Nuclear Regulatory Commission web page on tritium monitoring: http://www.nrc.gov/reactors/operating/ops-experience/grndwtr-contam-tritium.html