Radiation monitoring in Minnesota

December 1, 2011

Posted by Matt Ehling

Public Record Media became interested in seeking information about radiation exposure in Minnesota due to an Associated Press (AP) article published on June 21st, 2011. The article highlighted reports about radioactive tritium leaching into groundwater at or near U.S. nuclear plants. According to the Nuclear Regulatory Agency (NRC)’s web site:

Tritium is a mildly radioactive type of hydrogen that occurs both naturally and during the operation of nuclear power plants. Water containing tritium and other radioactive substances is normally released from nuclear plants under controlled, monitored conditions the NRC mandates to protect public health and safety. The NRC recently identified several instances of unintended tritium releases …

The NRC has produced several documents that deal with leaks and spills of tritium at NRC-licensed nuclear plants. One document – available in our Document Archive – lists spill or leak events that exceed the Environmental Protection Agency’s standard for drinking water safety (listed as 20,000 pCi/L). Minnesota’s Monticello nuclear plant is noted as the location of one such event, in 2009.

The NRC’s “tritium release list” observes the following about the leak data that it presents:

Tritium rapidly disperses and dissipates in the environment, and as a result, tritium from leaks and spills is typically not detected outside the facility boundary. The historical data indicates in only one instance, at Braidwood (Illinois) was tritium from a leak or spill found in the offsite environment in excess of 20,000 pCi/L.

The NRC also maintains that “all available information shows no threat to the public from the leaks.” However, the NRC’s data does demonstrate that such leaks are increasing, and that leak levels at some plants are extremely high.

Because of the attention brought to this issue by the AP article, we sought to learn whether Minnesota agencies had communicated with the NRC about tritium groundwater releases in the state. PRM submitted public data requests to the Minnesota Pollution Control Agency (MPCA) in June of this year, seeking such correspondence. The MPCA responded that they could find no records of such communication.

Our June MPCA request also sought to obtain any reports related to tritium contamination prepared by that agency. The MPCA directed us to the Minnesota Department of Health (MDH), which maintains an environmental monitoring program for radiation contamination. We filed a data request with the MDH, and received several reports.

After reviewing this batch of documents, we compiled the following summary from details contained in MDH reports, from the years 2005-2010.

Executive summary
During the past several years, MDH monitoring has not detected radiation levels that were elevated beyond state and federal standards, even during the period when the NRC noted an unusual tritium release at the Monticello nuclear plant. The MDH reports do not contain references to – or show correlated impacts from – the Monticello release event noted in the NRC’s “tritium release” report.

History of Minnesota’s radiation monitoring program
The MDH radiation monitoring program surveys radiation levels at several sites throughout the state of Minnesota. According to agency reports, individuals in Minnesota receive radiation doses from both natural and human-related activities. These human-related exposures include exposure to strontium-90 that “still exists from atmospheric nuclear testing in the 1950′s” as well as “scatter radiation from the Prairie Island” nuclear plant. (1) Overall radiation sampling in Minnesota began in 1953, due to above-ground nuclear testing conducted in the United States and elsewhere. (2)

The MDH Radiation Control Unit “monitors environmental radioactivity in Minnesota,” and is “designed to assess the impact of nuclear generating plants to the environment and the public over a period of time. Data collected is used to determine compliance with appropriate standards and establish trends.” Annual reports are generated for public review and consumption. (2)

If any increases in radiation are identified, “corrective actions are recommended to ensure that amounts do not exceed safe levels. Monitoring also allows the MDH to develop a database on radioactivity within the state that can be used as a baseline during emergencies.” (1)

The MDH environmental monitoring program consists of sample collection from locations at or near Minnesota’s two nuclear-generating plants. (1) The nature of the collected samples has varied slightly over time, but has included surface water monitoring, ambient gamma radiation monitoring, well water samples, air monitoring, and the observation of sensors near spent fuel storage casks. (1)

Vegetation monitoring was eliminated in 2008. (1) Such monitoring had been conducted for several years, but MDH personnel subsequently felt that monitoring for recent radiation contamination was better undertaken via air sampling. (3)

Monitoring equipment
The MDH measures radiation present in the air through samples taken near the Minnesota nuclear plants, but it also conducts “control” monitoring of background radiation via a rooftop air sampler in downtown St. Paul. (1)

Beginning in December 2005, the MDH air sampler was moved to the Freeman Office Building, 625 North Robert Street in Saint Paul, because the Department vacated its previous Minneapolis location at 717 Delaware St. According to MDH reports, the control sampler “is in a similar urban environment as the old one and is not expected to bias future data. (1)

Reports on air sampling note that, “Whenever applicable, naturally occurring Potassium-40 and Beryllium-7 are tracked as a means of quality control for accuracy of lab data. It is expected that these levels will remain somewhat constant throughout time.” (1)

Other MDH rooftop air samplers “are located near source points for radiation. The location of the Prairie Island air sampler is near Lock and Dam No. 3, downstream from the Prairie Island Nuclear Power Generating Plant. The air sampler at Monticello is located near the Monticello Xcel Training Center, downstream from the Monticello Nuclear Power Generating Plant.” (1)
The MDH also maintains detectors of various kinds near spent fuel storage casks, and at the perimeters of the nuclear plants. More information on these sensors is contained in the summaries below.

Summaries of results
Each annual MDH report contains a narrative summary of events during the year, along with compilations of radiation levels found in samples. Excerpts of the annual narratives are provided below, by date.

2005 MDH report
“No federal or state standards or guidelines were exceeded anywhere in the state, including near the nuclear electricity-generating plants.” (1)

“Data from radiation detection equipment at Prairie Island indicate that neutron levels increased because three casks were added to the Independent Spent Fuel Storage Installation (ISFSI) in 2005.” (1)

2006 MDH report
“In 2006, no federal or state standards or guidelines were exceeded anywhere in the state, including near the nuclear power generating plants.”

“Data shows that levels of Strontium-90 in milk, which resulted from previous above ground nuclear testing, are low and now below the detection limit of the isotopic analysis equipment. The median values for Strontium-90 were well within recommended safe levels according to the U.S. Food and Drug Administration (FDA) emergency guidelines for milk.” (3)

“Data from radiation detection equipment at Prairie Island indicate that neutron levels increased since last year. The increase is attributed to that fact that two casks were added to the Independent Spent Fuel Storage Installation (ISFSI) in 2006.” (3)

“The amount of exposure has been mitigated by the berms that were created when the ISFSI was established and remains dependent on the time spent near the ISFSI. For the purposes of determining dose, MDH assumed continuous presence of an individual at 700 meters from the center of the ISFSI.” (3)

“Dose calculations indicate that individuals in Minnesota receive less than one millirem per year from human-made radiation detected in the environment. The National Council on Radiation Protection and Measurements (NCRP) considers an annual dose of one mrem to be negligible.” (3)

2007-2008 MDH report
MDG produced a joint 2007-2008 report. This report was more sparing with its narrative detail than previous reports.

“In 2007 and 2008, no sample results within the current environmental monitoring program areas were found to exceed any federal or state standards or guidelines.” (4)

2009 MDH report
“In 2009, no sample results within the current environmental monitoring program areas were found to exceed any federal or state standards or guidelines.” (5)

“In the fall of 2008 Monticello began storing spent fuel in its own ISFSI on site. This ISFSI is monitored using an automatic switching, two Geiger-Mueller-tube based dose rate monitor called the Data Radiation Monitor (DRM). The DRM continuously measures gamma radiation dose rates. Readings are taken approximately every four seconds and transmitted via radio waves to a base computer. MDH connects to the base computer and receives dose rate readings. As with the Prairie Island monitoring system, alarm messages are sent if communication is disrupted or radiation levels are exceeded.” (5)

“Ambient gamma radiation levels are measured around the power plants by using thermoluminescent dosimeters (TLDs). MDH has placed TLDs beyond the plant’s boundaries to estimate the dose received by a member of the public if they were to be at that location continuously throughout the monitoring period.” (5)

“In 2009, one TLD located outside the spent fuel storage location at Prairie Island consistently read approximately twice the control levels, but still below regulatory levels. Investigation into the elevated readings continues and MDH plans to add a new TLD directly west of the current TLD in question in an attempt to determine the cause of the elevated readings.” (5)

“Dose rate readings from the DRM monitor were significantly reduced in February of 2009 following placement of concrete barriers across from the storage modules. Monticello Nuclear Generating Power Plant personnel report there is no intent to remove these barriers.” (5)

“Tritium values were below 238 pCi/L at both surface water sampling locations.” Likewise, “all well water sample results for 2009 were within the EPA and MDH standards and guidelines.” (5)

(NOTE – This was the year that the NRC reported a leak at Monticello in excess of 20,000 pCi/L)

2010 MDH report
“In 2010 the only program modification was the addition of one TLD near the Prairie Island Nuclear Generating Power Plant Training Center. One TLD located near the Prairie Island facility had readings above background for two consecutive quarters; 4th quarter of 2009 and 1st quarter of 2010.” (6)

Over the same time period the Prairie Island Nuclear Generating Power Plant Environmental Monitoring Program did not show elevated readings for the same area, nor the area closer to the plant and ISFSI. MDH staff investigated the area around the TLD and found nothing to indicate the elevated level. In the 3rd quarter of 2010 an additional TLD was placed near the Training Center, yet in the vicinity of the one previously showing elevated readings. (6)

As of the 2nd quarter of 2010, all TLD readings are at a consistent background level. (6)

All well water and community water sample results for 2010 were within the EPA and MDH standards and guidelines. (6)

(1) MDH 2005 report
(2) MDH 2007 report
(3) MDH 2006 report
(4) MDH 2007-2008 report
(5) MDH 2009 report
(6) MDH 2010 report