Report: Source of radioactive groundwater located; no contamination of drinking water, Mississippi River
The company in charge of decommissioning a nuclear power plant in Genoa says it has found the source of radioactive groundwater discovered last year and that the contamination did not affect drinking water or the nearby Mississippi River.
LaCrosseSolutions, a subsidiary of the nuclear waste disposal company EnergySolutions, in March reported elevated levels of tritium in a monitoring well at Dairyland Power Cooperative’s La Crosse Boiling Water Reactor (LACBWR), the state’s first nuclear power plant to undergo decommissioning.
Records show that tritium levels spiked in December 2017 in water samples taken about 25 feet below the ground. A sample from Feb. 1 registered 24,200 picocuries per liter, just below the Environmental Protection Agency’s limit for drinking water.
According to a report filed earlier this month with the Nuclear Regulatory Commission, the environmental consulting firm Haley & Aldrich traced the contamination to an exhaust vent installed in the former reactor building as part of the demolition. The vent was just above a pit of stormwater and melted snow.
EnergySolutions spokesman Mark Walker said tritium was released into the air inside the reactor building as concrete was broken into smaller pieces.
A radioactive isotope of hydrogen, tritium bonds with airborne water molecules. According to the report, water vapor from inside the plant condensed as it reached the outside air and combined with the runoff, which found its way into a shallow aquifer.
After the tritium was detected in the groundwater, the exhaust vents were directed upward, a new lined catch-basin was installed to capture the runoff, and groundwater tritium levels began to fall.
According to the report, the contamination returned to baseline levels in August.
“They shut it down and contained it,” said Tim Zeichert, a hydrogeologist with the Wisconsin Department of Natural Resources, which is overseeing an investigation of the spill. “They did everything they needed to do.”
Tritium did not affect onsite drinking water or the Mississippi River, according to the report. The consultants also concluded the release of tritium vapor did not pose a risk to human health.
Workers at Dairyland’s neighboring coal-fired generator were told on March 6 not to drink tap water at the plant, although test results indicated water from the on-site well was safe to drink.
Haley & Aldrich released dye into the groundwater to confirm their theory.
Both the NRC and DNR are still reviewing the report.
NRC spokeswoman Viktoria Mitlyng said the agency will likely issue its own findings on the incident later this winter. The DNR has not given a timeline for its report.
“We need to review things thoroughly on our end,” Zeichert said. “Especially something of this nature.”
Zeichert said EnergySolutions has done everything the agency asked.
Tritium is a common byproduct at nuclear reactors, where stray protons interact with hydrogen atoms in the water used to cool the fuel, said Jeff Bryan, a UW-La Crosse chemistry professor who teaches nuclear science. It also occurs naturally through the effects of cosmic radiation on the atmosphere.
“The sun makes sure we have kind of a constant supply of tritium,” Bryan said.
Compared to other radioactive material, tritium poses a lower risk to human health.
“It has a lot less energy,” Bryan said.
The ‘tractor reactor’
Built for the federal government by Allis-Chalmers, the 50-megawatt plant — sometimes called the “tractor reactor” — was the first in Wisconsin when it went online in 1967, intended to serve as a demonstration facility.
Dairyland, which provides electricity for about 250,000 co-op customers in Wisconsin, Minnesota, Iowa and Illinois, operated the plant until 1987 when it became too expensive to run the tiny but heavily regulated generator.
Over its two-decade life, LACBWR generated just over 4,000 megawatt-hours of electricity. For comparison, Wisconsin’s only active nuclear plant, Point Beach, generated about 9.6 million megawatt hours in 2017 alone.
The nuclear reactor vessel was removed in 2007 and taken to a burial site in South Carolina. In 2012, the spent fuel rods were moved to dry cask storage and are expected to remain at the site — at a cost of about $3 million a year — until the federal government develops a long-term storage facility.
Dairyland contracted with EnergySolutions in 2016 to remove the remaining buildings and transferred the site license to the Salt Lake City-based company, which used a similar license arrangement in decommissioning the Zion Nuclear Power Station near Chicago.
EnergySolutions planned to ship the contaminated rubble to low-grade nuclear waste disposal sites in Utah and Texas.
Exposure to radiation at the cleaned site must be below the NRC’s acceptable level of 25 millirem per year from a single source, which is about 2½ times the exposure from a chest X-ray.
With demolition complete, LaCrosseSolutions must now survey the site to ensure radioactivity is below NRC standards. NRC inspectors will then have to confirm those measurements before the site license can be terminated.
Walker said EnergySolutions expects to submit its final site report to the NRC in December.
Dairyland spokeswoman Deb Mirasola said the company has no immediate plans to use the 1.5-acre site, which is adjacent to a Dairyland coal-fired plant. Dairyland will continue to hold a license for the spent fuel.
In February, LaCrosseSolutions workers accidentally spilled 400 gallons of radioactive water into the Mississippi River when a garden hose was left overnight in a holding tank and siphoned out contaminated water.
The NRC determined the spill was a violation of federal regulations but did not issue a citation and said there was little risk to public health.