Answer to Question #8456 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
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