By RUSTY DENNEN
For the second time in 16 months, elevated levels of tritium have been found in groundwater at North Anna Power Station.
The sample, reported Tuesday by Dominion power to the Nuclear Regulatory Commission, contained 53,300 picocuries of tritium per liter of water. That is above the voluntary reporting threshold of 20,000 picocuries. A picocurie (pronounced PEE-ko curee) is one trillionth of a curie—a measurement of radioactivity.
Tritium is a weakly radioactive hydrogen isotope that is formed in nature, and also during the operation of nuclear power plants.
A Dominion official said there is no danger to plant workers or to the public.
According to the NRC, someone drinking water from a well with a level of 1,600 picocuries for a year would receive a radiation dose equal to 1 percent of that from a dental X–ray.
The report says hydrological studies at North Anna have determined that the groundwater in that area migrates away from Lake Anna, built in the 1970s to cool the plant’s reactors.
The report says there is “no increase in the projected annual [tritium] dose to the public,” and no sources of drinking water in the area.
Groundwater-monitoring sites outside the plant’s protected area showed no detectable levels of tritium, meaning there is no migration of the substance off-site.
The sample, taken at one of eight monitoring sites at the plant on the Louisa County shore of Lake Anna, was obtained as part of ongoing study to determine the source of tritium first reported to the state and the NRC in October 2010.
At that time, a monitoring-well sample showed a tritium concentration of 16,500 picocuries per liter. Normal for that site is 3,000 to 4,000 picocuries.
“It’s a very small amount, and is not migrating off-site,” said Richard Zuercher, spokesman for Dominion’s nuclear power operations.
Zuercher said the sample was taken between the Unit 1 containment building and its turbine building.
The underground circulation-water tunnel for Unit 2 was one known source of tritium. When the units were shut down because of the Aug. 23 earthquake, “We did extensive inspection in the tunnel and made repairs where water may have migrated out of the tunnel and into the soil,” Zuercher said.
He said that area is no longer considered a contributor to to the problem.
Excessive levels of tritium in groundwater have been a concern at nuclear power plants in recent years.
Leaking steam pipes caused tritium to leak into groundwater at Entergy Corp.’s Vermont Yankee plant. Elevated levels have also been reported at Entergy’s Pilgrim plant in Plymouth, Mass.
The Environmental Protection Agency’s drinking-water threshold is 20,000 picocuries. Nuclear plants must file written reports with the NRC for any levels over 30,000 picocuries.
North Anna has had a radiological monitoring program since Units 1 and 2 went online in 1978 and 1980, respectively. Wells have been monitored for tritium since 2006.LINK
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