Early Leak Detection External to Structures at Nuclear Power Plants (NUREG-2151)

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Publication Information

Manuscript Completed: December 2012
Date Published: April 2013

Prepared by:
Mark Fuhrmann and Joseph Kanney

Iouri Prokofiev, NRC Project Manager

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Abstract

Concerns about inadvertent releases of radioactive liquids to the environment from nuclear power plants have prompted consideration of ways to provide early leak detection in the subsurface external to the structures of the facilities. Approaches to this include the use of single-point sensors to detect changes in moisture content in the vadose zone. While many of these sensors are sensitive and relatively durable, they only interrogate about 1 liter of soil. Arrays of single-point sensors could provide adequate coverage of larger areas. Two-dimensional and three-dimensional geophysical methods provide information for much larger areas. These methods sense moisture or other parameters that may be related to leaks, such as changes in conductivity/resistivity, permittivity, or temperature. Use of cross-borehole geophysics may provide coverage of vertical planes of soil while horizontal boreholes (or horizontal tubes installed during construction) can be used to interrogate planes underneath areas of concern. Other techniques include detection of tritium in soil vapor and temperature changes using coaxial cables. Some of these methods can be made autonomous. The methods are critically reviewed and discussed with emphasis on practical application at nuclear power plants. The U.S. Nuclear Regulatory Commission (NRC) held a public workshop on February 15, 2012, to discuss many of these methods with experts and interested parties. Recommendations are made for NRC’s Long-Term Research Program.