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RULE §336.308Determination of Internal Exposure

(a) For purposes of assessing dose used to determine compliance with occupational dose equivalent limits, the licensee shall, when required under §336.316 of this title (relating to Conditions Requiring Individual Monitoring of External and Internal Occupational Dose), take suitable and timely measurements of:

  (1) concentrations of radioactive materials in air in work areas; or

  (2) quantities of radionuclides in the body; or

  (3) quantities of radionuclides excreted from the body; or

  (4) combinations of these measurements.

(b) Unless respiratory protection equipment is used, as provided in §336.321 of this title (relating to Use of Individual Respiratory Protection Equipment), or the assessment of intake is based on bioassays, the licensee shall assume that an individual inhales radioactive material at the airborne concentration in which the individual is present.

(c) When specific information on the physical and biochemical properties of the radionuclides taken into the body or the behavior of the material in an individual is known, the licensee may:

  (1) use that information to calculate the committed effective dose equivalent and shall document that information, if used, in the individual's record; and

  (2) upon prior approval in the license by the commission, adjust the DAC or ALI values to reflect the actual physical and chemical characteristics of airborne radioactive material (e.g., aerosol size distribution or density); and

  (3) 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 §336.359, Appendix B, of this title (relating to Annual Limits on Intake (ALI) and Derived Air Concentrations (DAC) of Radionuclides for Occupational Exposure; Effluent Concentrations; Concentrations for Release to Sanitary Sewerage).

(d) If the licensee chooses to assess intakes of Class Y material using the measurements given in subsection (a)(2) or (3) of this section, the licensee shall delay the recording and reporting of the assessments for periods up to seven months, unless otherwise required by §336.335 of this title (relating to Reporting Requirements for Incidents) or §336.352 of this title (relating to Reports of Exposures, Radiation Levels, and Concentrations of Radioactive Material Exceeding the Limits). This delay permits the licensee to make additional measurements basic to the assessments.

(e) If the identity and concentration of each radionuclide in a mixture are known, the fraction of the DAC applicable to the mixture for use in calculating DAC-hours shall be either:

  (1) the sum of the ratios of the concentration to the appropriate DAC value (e.g., D, W, or Y) from §336.359, Appendix B, of this title for each radionuclide in the mixture; or

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

(f) 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 DAC for the mixture shall be the most restrictive DAC of any radionuclide in the mixture.

(g) When a mixture of radionuclides in air exists, a licensee may disregard certain radionuclides in the mixture if:

  (1) The licensee uses the total activity of the mixture in demonstrating compliance with the dose limits in §336.305 of this title (relating to Occupational Dose Limits for Adults) and in complying with the monitoring requirements in §336.316(2) of this title; and

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

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

(h) When determining the committed effective dose equivalent, the following information may be considered:

  (1) To calculate the committed effective dose equivalent, the licensee may assume that the inhalation of one ALI, or an exposure of 2,000 DAC-hours, results in a committed effective dose equivalent of 5 rems (0.05 sievert) for radionuclides that have their ALIs or DACs based on the committed effective dose equivalent.

  (2) When the ALI (and the associated DAC) is determined by the nonstochastic organ dose limit of 50 rems (0.5 sievert), the intake of radionuclides that would result in a committed effective dose equivalent of 5 rems (0.05 sievert) (the stochastic ALI) is listed in parentheses in Table I of §336.359, Appendix B, of this title. In this case, the licensee may, as a simplifying assumption, use the stochastic ALI to determine committed effective dose equivalent. However, if the licensee uses the stochastic ALI, the licensee shall also demonstrate that the limit in §336.305(a)(1)(B) of this title is met.

Source Note: The provisions of this §336.308 adopted to be effective June 5, 1997, 22 TexReg 4588; amended to be effective September 14, 2000, 25 TexReg 8989

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