United States Nuclear Regulatory Commission - Protecting People and the Environment

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

monitoring requirements;

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


Page Last Reviewed/Updated Thursday, March 29, 2012