U.S. Nuclear Regulatory Commission
Question 437: The rule provides for disregarding certain
radionuclides in a mixture of radionuclides in air if three
conditions are met. The conditions are:
a. The licensee uses the total activity of the mixture in
demonstrating compliance with occupational dose limits and
b. The concentration of any radionuclide disregarded is
less than 10% of its derived air concentration (DAC); and
c. The sum of the percentages for all radionuclides
disregarded in the mixture does not exceed 30%.
As used in this provision, what is the intent of the phrase
"total activity of the mixture" and how is it to be
applied? Please provide an example that illustrates how
this provision may be properly used.
Answer: See the answer to Question 121 under the heading
10 CFR 20.1204. That answer states that the term "total
activity" in 10 CFR 20.1204 refers to "gross activity"
measurements that are correlated with other measurements of
individual radionuclides; an example of the use of this
provision is provided in that answer. (Reference: 10 CFR