Unless otherwise directed by NRC, DOE shall use the radiation weighting factors and tissue weighting factors in this Appendix to calculate the internal component of the annual committed effective dose equivalent for compliance with §§ 197.20 and 197.25 of this part. NRC may allow DOE to use updated factors issued after the effective date of this regulation. Any such factors shall have been issued by consensus scientific organizations and incorporated by EPA into Federal radiation guidance in order to be considered generally accepted and eligible for this use. Further, they must be compatible with the effective dose equivalent dose calculation methodology established in ICRP 26 and 30, and continued in ICRP 60 and 72, and incorporated in this appendix.
I. Equivalent Dose
The calculation of the committed effective dose equivalent (CEDE) begins with the determination of the equivalent dose, HT, to a tissue or organ, T, listed in Table A.2 below by using the equation:
where DT,R is the absorbed dose in rads (one gray, an SI unit, equals 100 rads) averaged over the tissue or organ, T, due to radiation type, R, and wR is the radiation weighting factor which is given in Table A.1 below. The unit of equivalent dose is the rem (sievert, in SI units).
Table A.1—Radiation weighting factors, wR
1
| Radiation type and energy range
2
| wR value
|
|---|
| Photons, all energies | 1
|
| Electrons and muons, all energies | 1
|
| Neutrons, energy
| |
| <10 keV | 5
|
| 10 keV to 100 keV | 10
|
| >100 keV to 2 MeV | 20
|
| >2 MeV to 20 MeV | 10
|
| >20 MeV | 5
|
| Protons, other than recoil protons, >2 MeV | 5
|
| Alpha particles, fission fragments, heavy nuclei | 20
|
The next step is the calculation of the effective dose equivalent, E. The probability of occurrence of a stochastic effect in a tissue or organ is assumed to be proportional to the equivalent dose in the tissue or organ. The constant of proportionality differs for the various tissues of the body, but in assessing health detriment the total risk is required. This is taken into account using the tissue weighting factors, wT in Table A.2, which represent the proportion of the stochastic risk resulting from irradiation of the tissue or organ to the total risk when the whole body is irradiated uniformly and HT is the equivalent dose in the tissue or organ, T, in the equation:
Table A.2—Tissue weighting factors, wT
| Tissue or organ
| wT value
|
|---|
| Gonads | 0.20
|
| Bone marrow (red) | 0.12
|
| Colon | 0.12
|
| Lung | 0.12
|
| Stomach | 0.12
|
| Bladder | 0.05
|
| Breast | 0.05
|
| Liver | 0.05
|
| Esophagus | 0.05
|
| Thyroid | 0.05
|
| Skin | 0.01
|
| Bone surface | 0.01
|
| Remainder |
a b 0.05
|
For internal irradiation from incorporated radionuclides, the total absorbed dose will be spread out in time, being gradually delivered as the radionuclide decays. The time distribution of the absorbed dose rate will vary with the radionuclide, its form, the mode of intake and the tissue within which it is incorporated. To take account of this distribution the quantity committed equivalent dose, HT(τ) where τ is the integration time in years following an intake over any particular year, is used and is the integral over time of the equivalent dose rate in a particular tissue or organ that will be received by an individual following an intake of radioactive material into the body:
for a single intake of activity at time t0 where HT(τ) is the relevant equivalent-dose rate in a tissue or organ at time t. For the purposes of this rule, the previously mentioned single intake may be considered to be an annual intake.
IV. Internal Component of the Annual Committed Effective Dose Equivalent
If the annual committed equivalent doses to the individual tissues or organs resulting from an annual intake are multiplied by the appropriate weighting factors, wT, from table A.2, and then summed, the result will be the internal component of the annual committed effective dose equivalent E(τ):
[73 FR 61288, Oct. 15, 2008]