180 Neb. Admin. Code, ch. 4, § 008

Current through September 17, 2024

Section 180-4-008 - DETERMINATION OF INTERNAL DOSE

Licensees must determine the internal dose as follows.

008.01TIMELY MEASUREMENTS. For purposes of assessing dose used to determine compliance with occupational dose equivalent limits, the licensee must, when required under 180 NAC 4-022 take suitable and timely measurements of:

(A) Concentrations of radioactive materials in air in work areas; or

(B) Quantities of radionuclides in the body; or

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

(D) Combinations of these measurements.

008.02INHALATION CONCENTRATION. Unless respiratory protective equipment is used, as provided in 180 NAC 4-028 or the assessment of intake is based on bioassays, the licensee must assume that an individual inhales radioactive material at the airborne concentration in which the individual is present.

008.03ADDITIONAL CONSIDERATIONS. When specific information on the physical and biochemical properties of the radionuclides taken into the body or the behavior or the material in an individual is known, the licensee may:

(A) Use that information to calculate the committed effective dose equivalent, and, if used, the licensee must document that information in the individual's record; and

(B) Upon prior approval of the Department, adjust the derived air concentration (DAC) or annual limit on intake (ALI) values to reflect the actual physical and chemical characteristics of airborne radioactive material, for example, aerosol size distribution or density; and

(C) Separately assess the contribution of fractional intakes of Class D, W, or Y compounds of a given radionuclide to the committed effective dose equivalent. See Appendix 4-B of 180 NAC 4.

008.04CLASSY MATERIAL INTAKE ASSESSMENT. If the licensee chooses to assess intakes of Class Y material using the measurements given in 180 NAC 4-008.01(B) or (C), the licensee may delay the recording and reporting of the assessments for periods up to seven months, unless otherwise required by 180 NAC 4-058 or 4-059. This delay permits the licensee to make additional measurements basic to the assessments.

008.05KNOWN NUCLIDES AND CONCENTRATION. If the identity and concentration of each radionuclide in a mixture are known, the fraction of the derived air concentration (DAC) applicable to the mixture for use in calculating derived air concentration (DAC)-hours must be either:

(A) The sum of the ratios of the concentration to the appropriate derived air concentration (DAC) value, D, W, or Y, from Appendix 4-B of 180 NAC 4 for each radionuclide in the mixture; or

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

008.06KNOWN NUCLIDES. 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 (DAC) for the mixture must be the most restrictive derived air concentration (DAC) of any radionuclide in the mixture.

008.07MIXTURE OF NUCLIDES. When 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 dose limits in 180 NAC 4-005 and in complying with the monitoring requirements in 180 NAC 4-022;

(B) The concentration of any radionuclide disregarded is less than 10% of its derived air concentration (DAC); and

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

008.08DETERMINING COMMITTED EFFECTIVE DOSE EQUIVALENT. Committed effective dose equivalent must be determined as follows:

(A) In order to calculate the committed effective dose equivalent, the licensee may assume that the inhalation of one annual limit on intake (ALI), or an exposure of 2,000 derived air concentration (DAC)-hours, results in a committed effective dose equivalent of 0.05 Sv (5 rem) for radionuclides that have their annual limit on intake (ALI)s or derived air concentration (DAC)s based on the committed effective dose equivalent; and

(B) For an annual limit on intake (ALI), and the associated derived air concentration (DAC) determined by the nonstochastic organ dose limit of 0.5 Sv (50 rem), the intake of radionuclides that would result in a committed effective dose equivalent of 0.05 Sv (5 rem), the stochastic annual limit on intake (ALI) is listed in parentheses in Table I of Appendix 4-B of 180 NAC 4. The licensee may, as a simplifying assumption, use the stochastic annual limit on intake (ALI) to determine committed effective dose equivalent. However, if the licensee uses the stochastic annual limit on intake (ALI), the licensee must also demonstrate that the limit in 180 NAC 4-005.01(A)(ii) is met.

180 Neb. Admin. Code, ch. 4, § 008

Amended effective 6/7/2021