Soil Contamination at Vermont Yankee

The January 7, 2010 report of tritium in groundwater at Vermont Yankee marked an unintentional underground release of radioactive material. This also meant that other radioisotopes may have contaminated the environment. Soil testing has confirmed this.

Although the soil at Vermont Yankee has been contaminated with radioactive materials, there is no known exposure or risk to the public.

Soil Analysis

Strontium-90, cesium-137, zinc-65, manganese-54, and cobalt-60 have all been detected in soil that was collected for laboratory analysis. Soil samples were taken from various locations and depths below the excavation area outside the Advanced Off-Gas (AOG) pipe tunnel that was found to have caused this leak.

Laboratory Results & Analyses

Data listings and charts of the separately performed Vermont Department of Health and Vermont Yankee laboratory analyses.

About the sampling and analyses

These radioisotopes have all been detected at greater concentrations and deeper in the ground than would be expected from nuclear fallout or weapons testing long ago. This is evidence that radioisotopes in addition to tritium washed out of the AOG pipe tunnel into the environment with the leaking nuclear reactor water.

Soil testing done immediately after another leak was discovered by Vermont Yankee on May 28 also detected these as well as a number of other radioisotopes that decay quickly and are no longer detectable within hours or days: chromium-51, cobalt-58, zinc-69, niobium-95, rhodium-105, barium-140, lanthanum-140 (all metals), and xenon-131 (a noble gas).

The concentrations of strontium-90 and cesium-137 found in soil samples taken from the excavation in the area of the AOG pipe tunnel are much greater than would be expected from fallout. In the Feb. 26 set of soil samples, both were measured at much greater concentrations than are found in surface soils in Vermont and around the world.

In the March 17 and 18 set of soil samples, cesium-137 was found at as much as 75 times what would be expected in surface soils. Analysis by Vermont Yankee of concrete mud and construction debris in the AOG pipe tunnel also confirmed the presence of cesium-137.

As part of its ongoing environmental surveillance, the Vermont Department of Health has tested soil samples from two sites in the state not associated with Vermont Yankee and confirmed cesium-137 at concentrations consistent with past nuclear fallout. In 2008, cesium-137 was measured at 86 and at 168 picocuries per kilogram (pCi/kg).

More testing is underway. At the request of the Health Department, samples of mud and construction debris from within the tunnel were also taken for analysis. Split samples are being analyzed by the Department of Health Laboratory. Samples will also be analyzed by an independent laboratory under contract with the Health Department for “hard to detect” radionuclides such as strontium-90, iron-55 and nickel-63.

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About Strontium-90 and Cesium-137

Strontium-90 and cesium-137 are both products of nuclear fission, and do not occur naturally in the environment. These isotopes also give off radiation and decay over a long period of time. The “half life” is the length of time it takes to decay to one-half of its original concentration. Strontium-90 has a half life of 29 years, and cesium-137 has a half-life of 30 years.

Strontium-90 is considered one of the more hazardous of the radionuclides associated with nuclear reactors. It is a moderately strong beta emitter. This means that its radiation can pass through the human body, stopped only by a layer of wood, a sheet of aluminum, or sometimes clothing. It behaves chemically much like calcium, and tends to concentrate in the bones and teeth and bone marrow. Strontium-90 is linked to bone cancer, cancer of the soft tissue near bone, and leukemia.

Cesium-137 is a moderately strong gamma emitter.This means that its radiation can pass through the human body, stopped only by a lead shield or several feet of concrete.

For more information on strontium-90:
http://www.epa.gov/radiation/radionuclides/strontium.html  http://www.ead.anl.gov/pub/doc/Strontium.pdf

For more information on cesium-137: http://www.epa.gov/radiation/radionuclides/cesium.html http://www.ead.anl.gov/pub/doc/Cesium.pdf

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About Zinc-65, Manganese-54, Cobalt-60

Zinc-65, manganese-54 and cobalt-60 are all corrosion products. They are produced when steel components in the nuclear reactor corrode. Tiny amounts of the corroded metals circulate in the reactor water, and may be released during re-fueling or maintenance operations.

All of these isotopes give off radiation and decay over time. The “half life” is the length of time it takes to decay to one-half of its original concentration. Zinc-65 has a half life of 244 days. Manganese-54 has a half life of 313 days. Cobalt-60 has a half life of 5.3 years and is a strong gamma emitter. This means that its radiation can pass through the human body, and is stopped only by a lead shield or several feet of concrete.

For more information on cobalt-60:  http://www.epa.gov/radiation/radionuclides/cobalt.html http://www.ead.anl.gov/pub/doc/Cobalt.pdf

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