Tritium and Effluent Release Issue

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Initial Event

On Nov. 22, 2022, during routine sampling of monitoring wells that detect underground leaks on-site, Xcel identified elevated tritium levels in one well. The well monitors a section between the reactor and turbine buildings.

Xcel notified the State of Minnesota. The notification to the state triggered an Event Notification to the NRC. The NRC requires licensees to notify the agency of any notifications to other government agencies. The leak did not trigger the NRC’s notification criteria – because it did not exceed any NRC limits or violate federal requirements.

NRC resident inspectors were also informed by Xcel of the elevated levels and began monitoring the company’s actions to determine the source of the leak. 

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NRC’s Response

NRC resident inspectors and regionally based experts talked to the site to ensure the NRC thoroughly understood the event. Inspectors assessed the leak and determined the leak had no impacts on public health and safety and had no pathway to a drinking water supply.

The NRC followed the progress as the site’s workers identified and traced the source of the leak and stopped it and made sure the site established remediation plans.

The NRC continues to monitor the sample results from on-site wells.

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Remediation Activities

NRC inspectors monitored licensee’s actions and agreed with the company’s conclusions about the source of the leak. The company determined the leak occurred from a contaminated pipe that goes across a small gap between the reactor and turbine building and is below grade (underground) where it goes across this gap.

NRC inspectors also reviewed and observed the licensee efforts to stop the leak. Subsequently, the site began remediation activities by pumping the tritiated groundwater into on-site storage tanks and the plant’s installed waste processing systems. NRC resident and health physics inspectors continued to review the site’s remediation work and plans.

The site continues to sample and analyze groundwater from various monitoring wells to ensure the extent of the tritium is well understood.

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Tritium Levels and Limits

Was the public in danger?

No, the public was safe as the leak did not compromise plant or public safety. NRC inspectors at the site and specialists in the area of health physics continue to closely monitor the plant’s response to the leak and will continue to monitor the sites actions in response. The total tritium activity that leaked into the groundwater is about 8 Ci. A Ci is a measurement of how radioactive the water is. An exit sign with tritium will usually have about 25 Ci of tritium.

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How will you guarantee public safety if the tritiated water migrates off site?

The volume of tritium leaked does not pose a threat to the public or the environment. There is no potential for the leak to impact the public health and safety. However, the NRC will continue to monitor tritium levels in groundwater monitoring wells for indications of an offsite release and ensure the site is taking appropriate action to keep the dose to the public not only below NRC limits but as low as reasonably achievable.

The site has implemented a groundwater recovery program designed to capture the contaminated groundwater prior to leaving the site boundary, and routinely samples monitoring wells to verify the location of the plume. If the entire amount were to get to the Mississippi River, the impact to the public would be small. This dose is so small, it can’t be measured and constitutes a small portion of the 300 mrem per year that an average person receives from background radiation.

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What are the NRC’s tritium limits?

The NRC regulates offsite releases by requiring licensees to make sure the dose to the public from tritium and other isotope releases does not exceed 100 mrem per year and is as low as reasonably achievable. More information about tritium releases can be found on the NRC webpage for groundwater contamination.

Are public drinking water wells near the site at risk of becoming contaminated?

No, drinking water wells are not at risk of becoming contaminated. There are no drinking water wells between the location of the leak and the Mississippi River, which is the direction the contaminated groundwater moves.

The NRC requires Xcel to routinely collect samples from the environment around the site and analyze it for radioactive material. Samples include drinking water wells on and off site, the drinking water supply for Minneapolis, and surface water samples from the Mississippi River. This program is known as the Radiological Environmental Monitoring Program (REMP), which verifies that there is no negative impact from the plant to the environment or the public from radioactive material.

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Public Notifications

Was information about the tritium leak public? Why did it take months to talk about the leak?

The Event Notification from Xcel was posted on the NRC’s website. In this case, the NRC was formally notified by Xcel because the company notified the State of Minnesota about the tritium leak. The NRC requires licensees to notify the agency of any notifications to other government agencies. The leak did not trigger the NRC’s notification criteria – because it did not exceed any NRC limits or violate federal requirements. The NRC responded to public and media questions and concerns. The NRC also created a preliminary notification in response to the interest. Since then, NRC inspectors have documented their findings in a publicly available inspection report.

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How will the public know if there is an issue at the plant?

Information can always be found on the website including specifics for each plant in NRC inspection reports. The NRC has and will continue to make information public when the agency becomes aware and responds to a serious safety issue at the plant or any safety issue that can impact public health. The NRC will work with the state, plant and designated responders to notify the public immediately if a radioactive release could exceed NRC requirements.

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Has the NRC considered changing its criteria for reporting situations to the public? 

The NRC is committed to keeping the public informed about the agency’s processes, inspections and actions. The agency also continually reviews its regulations and requirements and changes them as a result of these reviews when appropriate. We remain committed to notifying the public of situations that could potentially compromise plant or public safety when they occur. In addition, we make information publicly available about how we conduct our business by documenting inspections, notifications from license holders and other agency activities. 

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Effluent Releases

Does the NRC allow plants to make effluent releases?

NRC-licensed facilities may discharge low level liquid and gaseous radiological wastes into the environment provided that dose limits to members of the public (see 10 CFR 20.1301) are not exceeded and are as low as reasonably achievable (ALARA).

As part of the oversight process, the NRC also requires annual reports from the licensee that record and analyze the release of effluents at discharge points such as plant stack for gaseous releases or discharge pipe for liquid releases. Companies are required to ensure they meet ALARA, measure and document the radiation releases in a publicly available REMP reports ensuring no negative impact to the public or environment.

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Who is responsible for determining how effluents are released from Monticello?

Xcel is responsible for being compliant with NRC release requirements but separate of the NRC they may also have to follow other state or local requirements.

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What are the NRC’s regulations for radioactive releases?

Information on the NRC's Regulations for Radioactive Release:

The NRC’s regulations governing radioactive releases are based on dose to the public, not the volume of the release (see 10 CFR 20.2001; 20.1301; 20.2003; 20.2004; 20.2005; and 10 CFR 35.92). The same requirements apply to decommissioning and operating reactors.

Key Technical NRC Regulatory Guides (RG) on Radiological Effluents:

  • RG 1.109, Calculation of Annual Doses to Man from Routine Releases of Reactor Effluents for the Purpose of Evaluating Compliance with 10 CFR Part 50, Appendix I, provides the detailed implementation guidance for demonstrating that radioactive effluents conform to the ALARA design objectives of 10 CFR Part 50, Appendix I.
  • RG 1.21, Measuring, Evaluating, and Reporting Radioactive Materials in Liquid and Gaseous Effluents and Solid Waste, addresses the measuring, evaluating, and reporting of effluent releases, solid radioactive waste shipments, and public dose from nuclear power plants.
  • RG 4.1, Radiological Environmental Monitoring for Nuclear Power Plants, discusses principles and concepts important to environmental monitoring at nuclear power plants. The RG provides guidance on radiological environmental monitoring programs for routinely monitored exposure pathways and annual reporting to the NRC

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Related Documents

Environmental Monitoring fact sheet

Environmental Monitoring Program Video

Backgrounder on Tritium, Radiation Protection Limits and Drinking Water Standards

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Page Last Reviewed/Updated Saturday, July 15, 2023