Health Physics Questions and Answers - Question 437

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 20.1204)