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21 November 2009

Answer to Question #8456 Submitted to "Ask the Experts"

Category: Decommissioning — Release Criteria and Guidelines

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

Regarding Regulatory Guide 1.86, do you have a referenced definition for the phrase "associated decay products" for the uranium group in Table 1?

Thank you for your question pertaining to Regulatory Guide (RG) 1.86, "Termination of Operating Licenses for Nuclear Reactors." Table 1 of RG 1.86 lists acceptable surface contamination levels for four groupings of radionuclides. The first radionuclide grouping is listed as "U-nat, U-235, U-238, and associated decay products." This grouping refers to processed uranium, i.e., uranium that has been separated from its longer half-life decay products by extraction of the uranium from the naturally occurring ore state. So U-nat is composed of uranium-238, uranium-235, and uranium-234 at relative natural activity ratios of roughly 1.0/0.05/1.0, and contains the short half-life progeny of uranium-238, i.e., thorium-234, protactinium-234, and protactinium-234m, in secular equilibrium with the uranium-238.

Your specific question referred to a referenced definition for the phrase "associated decay products" for the uranium group in Table 1 of the RG. The best I was able to find was a letter dated 26 May 1994 from Mr. James D. Berger (ORISE) to Mr. David Fauver (NRC) with subject line "Interpretation of Surface Contamination Guidelines - Draft 5." I could not find this material published in any NRC documents.

Hope this helps.

Eric W. Abelquist, CHP

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