Minimum Detectable Concentrations with Typical Radiation Survey Instruments for Various Contaminants and Field Conditions (NUREG-1507, Revision 1)

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Publication Information

Manuscript Completed: August 2020
Date Published: August 2020

Prepared by:
E.W. Abelquist*
J.P. Clements
A.M. Huffert
D.A. King*
T.J. Vitkus*
B.A. Watson

Division of Decommissioning, Uranium Recovery, and Waste Programs
Office of Nuclear Material Safety and Safeguards
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

*Oak Ridge Associated Universities
1299 Bethel Valley Road Oak Ridge, TN 37830

John Clements, NRC Project Manager

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Abstract

This document describes and quantitatively evaluates the effects of various factors on the detection sensitivity of commercially available portable field instruments being used to conduct radiological surveys in support of decommissioning. Facilities licensed by the U.S. Nuclear Regulatory Commission (NRC) must demonstrate that residual radioactivity at their site meets radiological dose-based criteria for license termination, such as the criterion of 25 millirem per year for unrestricted release in "Radiological Criteria for License Termination" (the License Termination Rule), Subpart E to Title 10 of the Code of Federal Regulations Part 20, "Standards for Protection against Radiation." These dose-based criteria are often expressed as concentration-based screening values for structural surface contamination in units of disintegrations per minute per 100 square centimeters and for surface soil contamination in units of picocuries per gram. As described in NUREG-1575, Revision 1, "Multi-Agency Radiation Site Survey and Investigation Manual (MARSSIM)," issued August 2000, radiological survey instruments are used to measure radiation levels that are then directly compared to the release criteria.

Since publication of the original NUREG-1507 in 1998, licensees have increasingly used additional survey instrumentation and data capture tools, including global positioning system (GPS) and geographic information system (GIS) technologies. Survey techniques and calculation methodologies have changed over the interim period along with the introduction of advanced radiation survey instruments. This document introduces some concepts related to GPS/GIS based techniques and methodologies along with considerations for detection efficiency calculations, background interferences, signal degradation, and other topics associated with radiation survey instrumentation.

The purpose of this document is three-fold. First, the data were used to determine the validity of the theoretical minimum detectable concentrations that licensees calculate by using traditional a priori decision rules and to discuss GPS/GIS technologies that support a posteriori decision rules. Second, the results of the study provide guidance to licensees for (a) selection and proper use of portable survey instruments and (b) understanding the effect of field conditions and the limitations and capabilities of those instruments. Third, the NUREG emphasizes the use of data quality objectives that are developed while considering project- and instrument-specific inputs.