United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

U.S. Nuclear Regulatory Commission

Question 403: NRC Form 5 (Item No. 10) provides for

listing of specific radionuclides in intakes that

contribute to the recorded committed effective dose

equivalent (CEDE). When determining the CEDE only

significantly irradiated organs need be included in the

calculations [10 CFR 20.1202 (b) (3)]. An organ is

considered to be significantly irradiated if the product of

the weighting factor and committed dose equivalent, per

unit intake, is greater than 10% of the maximum weighted

value of committed dose equivalent (CDE), per unit intake

[Footnote 1 to 20 CFR 20.1202 (b) (3)]. Similarly, an

isotope need not be considered to be in an airborne mixture

if the concentration of any radionuclide is less than 10%

of its DAC, and the sum of the percentages of the

disregarded radionuclides is less than 30% [10 CFR 20.1204

(g)]. Given these two examples of cut off levels, can a

licensee disregard the contribution a radionuclide makes to

the CEDE, with regard to recording and reporting specific

radionuclides, if it is less than 10% of the total CEDE

resulting from uptake of a mixture, and the sum of the

disregarded radionuclides is less than 30%? In this way

insignificant doses, the addition of which imply greater

precision than exists for internal dosimetry, can be

disregarded without compromising sound radiological

practices.



Answer: No. The statements concerning significantly

irradiated organs [in 10 CFR 20.1202 (b) (3) and Footnote

1] apply to compliance with requirements for summation of

external and internal dose and are not relevant to cutoffs

of radionuclides used in intake calculations. The

statement in the question concerning the provisions of 10

CFR 20.1204 (g) is incorrect; it does not include the

necessary condition of 10 CFR 20.1204 (g) (1) concerning

use of the "total activity" in demonstrating compliance.

[See the answer to Question 121 for clarification of 10 CFR

20.1204 (g).] There is no basis in the regulations for the

proposed cutoff in the calculation of the CEDE.

(References: 10 CFR 20.2106, 10 CFR 20.2206, Regulatory

Guide 8.7).









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