| (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.
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