Iowa Admin. Code r. 641-40.18 - Determination of internal exposure
(1) For purposes of assessing dose used to
determine compliance with occupational dose equivalent limits, the licensee
shall, when required pursuant to 40.37(136C), 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.
(2) Unless respiratory protective equipment
is used, as provided in 40.50(136C), 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.
(3) 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:
a. Use that information to
calculate the committed effective dose equivalent, and, if used, the licensee
shall document that information in the individual's record; and
b. Upon prior approval of the agency, adjust
the DAC or 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 B.
(4) If
the licensee chooses to assess intakes of Class Y material using the
measurements given in 40.8(1)"b" or
40.8(1)"c," the licensee may delay the recording and reporting
of the assessments for periods up to seven months, unless otherwise required by
40.96(136C) or 40.97(136C). This delay permits the licensee to make additional
measurements basic to the assessments.
(5) 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:
a. The sum of the ratios of the concentration
to the appropriate DAC value, that is, D, W, or Y, 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 DAC value 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 DAC for the mixture shall be the
most restrictive DAC of any radionuclide in the mixture.
(7) 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 40.15(136C) and
in complying with the monitoring requirements in 40.37(136C), and
b. The concentration of any radionuclide
disregarded is less than 10 percent of its DAC, 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. In order to calculate
the committed effective dose equivalent, the licensee or registrant 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 rem (0.05 Sv) for radionuclides that
have their ALIs or DACs based on the committed effective dose
equivalent.
b. For an ALI and the
associated DAC determined by the nonstochastic organ dose limit of 50 rem (0.5
Sv), the intake of radionuclides that would result in a committed effective
dose equivalent of 5 rem (0.05 Sv), that is, the stochastic ALI, is listed in
parentheses in Table I of Appendix B. The licensee or registrant may, as a
simplifying assumption, use the stochastic ALI to determine committed effective
dose equivalent. However, if the licensee or registrant uses the stochastic
ALI, the licensee or registrant shall also demonstrate that the limit in
40.15(1)"a"(2) is met.
Notes
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