A Note from Larry Smith at Vermont Yankee
February 19, 2010
Vermont Yankee engineers and technicians continue their investigation into the source of tritium in the plant’s groundwater.
Today’s inspection of the Advanced Off Gas concrete pipe tunnel using a boroscope revealed little change in conditions over the past week. Some water can still be seen dripping from pipe insulation and flowing towards the drain where it is then collected in a sump and removed. Plans are being developed to test for leakage paths to the ground from the tunnel floor using pure water. 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 so that technicians might be able to observe any leakage paths revealed by the dye. Monitoring tritium concentrations in the well installed in this area (GZ-10) will continue through the excavation process. Thus far, the well monitoring data is not conclusive as to whether the AOG tunnel is the source of tritium in groundwater at the site and the investigation of this and other potential sources is ongoing.
Engineers and vendor experts continue to finalize the plans for the adjustments to the design for shoring and bracing work at the AOG building excavation site. Today, work was completed to support an electric cable duct so soil can be removed underneath it during excavation. Since the excavation site has been expanded from the original design, work on drilling holes for the support piers continues. Materials required for the work have arrived onsite and will be moved into the excavation area tomorrow. The new design accounts for all the necessary worker and nuclear safety requirements, and allows more flexibility in how the shoring supports are installed. Erection of the enclosure building walls is in progress. The roof section will be installed after the shoring is in place, as this work requires lifting the pieces into the excavation area using a crane.
The installation of new monitoring wells continues. The first deep well, GZ-13D is complete and in the process of being developed. Work on well GZ-14D commenced today. Digging for two additional shallow groundwater monitoring wells continues. The information from these new wells will help engineers and hydrology experts better understand groundwater flows beneath the site.
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.
For more details on the tritium investigation, the Vermont Department of Health has a thorough status report on the investigation at this web link: https://email.entergy.com/exchweb/bin/redir.asp?URL=http://healthvermont.gov/enviro/rad/yankee/tritium.aspxhttp://healthvermont.gov/enviro/rad/yankee/tritium.aspx
Also helpful is the Nuclear Regulatory Commission web page on tritium monitoring: https://email.entergy.com/exchweb/bin/redir.asp?URL=https://email.entergy.com/exchweb/bin/redir.asp?URL=http://www.nrc.gov/reactors/operating/ops-experience/grndwtr-contam-tritium.htmlhttp://www.nrc.gov/reactors/operating/ops-experience/grndwtr-contam-tritium.html
Laurence M. Smith
Manager of Communications
Entergy Nuclear Vermont Yankee 802-258-4118
lsmit14@entergy.com
February 19, 2010 Vermont Yankee Tritium Investigation Update
AOG Excavation
Preparations for the new approach to the excavation near the Advanced Off Gas (AOG) system area continued today. The new approach is needed to make sure the excavation area is safely shored up before work proceeds.
AOG Pipe Tunnel
Water appears to be still leaking from a source within the AOG Pipe Tunnel. There is visible movement of water within the tunnel, which can only be seen using a boroscope inserted through the concrete wall of the tunnel. The AOG pit sump to which the pipe tunnel drains is collecting about 100 gallons each day before being pumped from the sump to the Rad Waste Building.
Well Test Results
Vermont Yankee reports the following water sampling tests results for today: (All measurements are in picocuries per liter.)
GZ-3: 30,233
GZ-4: 2,709
GZ-7: 973,094
GZ-10: 1.993 million
GZ-12: 13,547
GZ-14: 119,206
GZ-15: 355,155
Note about Cobalt-60 and other Radioisotopes
There are often reports that cobalt-60 or other radioactive materials have been found in samples. These reports so far are of water within plant buildings or systems. It is expected that most nuclear plant process water will have cobalt-60 and other radioactive materials in it. It would NOT be expected to find these other radionuclides in the environment outside of plant systems, structures or buildings except near the source of a leak. However, to monitor this, water and soils are being tested for all these other radionuclides.
To date, tritium is the only radionuclide that has been detected. Tritium contamination has been detected in seven specific groundwater monitoring wells on-site at Vermont Yankee. There has been no tritium or any other nuclear plant-related radionuclide detected in drinking water wells on or off-site.
New Groundwater Monitoring Wells
Well drilling continues, with new coupled wells GZ-13D and GZ-14D the furthest along. Wells GZ-16 and GZ-19 are planned to be next in line.
