[Code of Federal Regulations]
[Title 10, Volume 1]
[Revised as of January 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 10CFR20.1204]

[Page 331-332]
 
                            TITLE 10--ENERGY
 
                CHAPTER I--NUCLEAR REGULATORY COMMISSION
 
PART 20--STANDARDS FOR PROTECTION AGAINST RADIATION--Table of Contents
 
                   Subpart C--Occupational Dose Limits
 
Sec. 20.1204  Determination of internal exposure.

    (a) For purposes of assessing dose used to determine compliance with 
occupational dose equivalent limits, the licensee shall, when required 
under Sec. 20.1502, 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 protective equipment is used, as provided in 
Sec. 20.1703, 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 or 
the material in an individual is known, the licensee may--
    (1) 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
    (2) Upon prior approval of 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 (see appendix B to 
part 20) to the committed effective dose equivalent.
    (d) If the licensee chooses to assess intakes of Class Y material 
using the measurements given in Sec. 20.1204(a)(2) or (3), the licensee 
may delay the recording and reporting of the assessments for periods up 
to 7 months, unless otherwise required by Sec. Sec. 20.2202 or 20.2203, 
in order to permit 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 must be either--
    (1) The sum of the ratios of the concentration to the appropriate 
DAC value (e.g., D, W, Y) from appendix B to part 20 for each radio-
nuclide 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 must be the most restrictive DAC of 
any radionuclide in the mixture.
    (g) When a mixture of radionuclides in air exists, licensees 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 Sec. 20.1201 and in 
complying with the monitoring requirements in Sec. 20.1502(b), and
    (2) The concentration of any radionuclide disregarded is less than 
10 percent of its DAC, and
    (3) The sum of these percentages for all of the radionuclides 
disregarded in the mixture does not exceed 30 percent.
    (h)(1) In order 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 Sv) 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 Sv), the intake of 
radionuclides that would result in a committed effective dose equivalent 
of 5 rems (0.05 Sv) (the stochastic ALI) is

[[Page 332]]

listed in parentheses in table 1 of appendix B to part 20. In this case, 
the licensee may, as a simplifying assumption, use the stochastic ALIs 
to determine committed effective dose equivalent. However, if the 
licensee uses the stochastic ALIs, the licensee must also demonstrate 
that the limit in Sec. 20.1201(a)(1)(ii) is met.

[56 FR 23396, May 21, 1991, as amended at 60 FR 20185, Apr. 25, 1995]