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21 November 2009

Answer to Question #949 Submitted to "Ask the Experts"

Category: Decommissioning — Release Criteria and Guidelines

The following question was answered by an expert in the appropriate field:

What are the maximum levels for alpha, beta, gamma, and tritium radiation at a low-level storage site that is being decommissioned? The values should be U.S. federal or U.S. levels.

Assuming that the U.S. Nuclear Regulatory Commission (NRC) decommissioning criteria apply, the criteria for unrestricted release is 25 mrem y^-1 and ALARA. The concentration limits for particular radionuclides that equate to 25 mrem y^-1 can be determined from exposure pathway modeling (that is, RESRAD). Therefore, the decommissioning criteria can be expressed in terms of radionuclide concentrations (derived concentration guideline levels, or DCGLs) once modeling is performed. The NRC has published (in the Federal Register on 11/18/98 and 12/7/99) generic DCGLs based on conservative modeling assumptions for a number of radionuclides—for example, tritium is 1.28×10⁸ dpm/100 cm² on surfaces and 110 pCi g^-1 in soil. There are no DCGLs for gross alpha, beta, or gamma levels; the licensee must establish the specific nature of the contamination in order to demonstrate compliance.

Eric Abelquist, PhD, CHP

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