NAC459.3275. Determination of compliance with limits for occupational doses.

     1. For the purposes of assessing the dose used to determine compliance with the limits for occupational doses set forth in NAC 459.325, a licensee shall, if required pursuant to subsection 2 of NAC 459.339, take suitable and timely measurements of:

     (a) Concentrations of radioactive materials in the air in work areas;

     (b) Quantities of radionuclides in the body;

     (c) Quantities of radionuclides excreted from the body; or

     (d) Any combination of the measurements listed in paragraphs (a), (b) and (c).

     2. Unless a respiratory protective device is used or the assessment of intake is based on bioassays, the licensee shall assume that a person inhales radioactive material at the airborne concentration in which the person is present.

     3. When specific information on the physical and biochemical properties of the radionuclides taken into the body or the behavior of the material in a person is known, the licensee may:

     (a) Use that information to calculate the committed effective dose equivalent;

     (b) Upon prior approval of the Division, adjust the values for the derived air concentration or the annual limit on intake to reflect the actual physical and chemical characteristics of airborne radioactive material; and

     (c) Separately assess the contribution of fractional intakes of compounds of a given radionuclide in Class D, W or Y to the committed effective dose equivalent.

Ê If a licensee uses the information to calculate the committed effective dose equivalent pursuant to paragraph (a), the licensee shall document that information in the record of the person.

     4. If the licensee chooses to assess intakes of material in Class Y using the measurements taken pursuant to paragraph (b) or (c) of subsection 1, the licensee may delay the recording and reporting of the assessments for not more than 7 months in order to make additional measurements basic to the assessments, unless he or she is otherwise required to record and report the assessments by NAC 459.3695 or 459.371.

     5. If the identity and concentration of each radionuclide in a mixture are known, the fraction of the derived air concentration applicable to the mixture that is used to calculate derived air concentration-hours must be:

     (a) The sum of the ratios of the concentration to the appropriate value for the derived air concentration from Appendix B for each radionuclide in the mixture; or

     (b) The ratio of the total concentration for all radionuclides in the mixture to the most restrictive value for the derived air concentration for any radionuclide in the mixture.

     6. If the identity of each radionuclide in a mixture is known, but the concentration of one or more of the radionuclides in the mixture is not known, the derived air concentration for the mixture must be the most restrictive derived air concentration of any radionuclide in the mixture.

     7. If a mixture of radionuclides in air exists, a licensee may disregard certain radionuclides in the mixture if:

     (a) The licensee uses the total activity of the mixture in demonstrating compliance with the limits specified in NAC 459.325 and in complying with the monitoring requirements specified in subsection 2 of NAC 459.339;

     (b) The concentration of any radionuclide disregarded is less than 10 percent of its derived air concentration; and

     (c) The sum of these percentages for all of the radionuclides disregarded in the mixture does not exceed 30 percent.

     8. When determining the committed effective dose equivalent, the following information may be considered:

     (a) The licensee or registrant may assume that the inhalation of one annual limit on intake, or an exposure of 2,000 derived air concentration-hours, results in a committed effective dose equivalent of 5 rems for radionuclides that have their annual limits on intake or derived air concentrations based on the committed effective dose equivalent.

     (b) For an annual limit on intake and the associated derived air concentration determined by the nonstochastic organ dose limit of 50 rems, the intake of radionuclides that would result in a committed effective dose equivalent of 5 rems is listed in parentheses in Table I of Appendix B. In this case, the licensee may use the stochastic annual limit on intake to determine the committed effective dose equivalent. If the licensee uses the stochastic annual limit on intake, the licensee shall also demonstrate that the limits specified in subparagraph (2) of paragraph (a) of subsection 1 of NAC 459.325 are met.

     (Added to NAC by Bd. of Health, eff. 1-18-94)