Question 396: The Appendix B tables of the revised Part 20
include ALIs and DACs for daughter radionuclides, in
contrast to the Appendix B tables in the "old" Part 20,
which do not include these daughter radionuclides. For
example, ALIs and DACs for rubidium-88 and cesium-138 are
listed. Are the listed ALIs and DACs expected to be
considered separately with regard to posting and other
requirements in the revised Part 20?
Answer: Yes. However, the statements preceding the
question itself may reflect misunderstandings; these
possible misunderstandings are addressed in the following
discussion.
The Appendix B tables of both "old" and "revised" Part 20
do include many "daughter radionuclides." The tables of
"revised" Part 20 include more radionuclides, and therefore
more daughter radionuclides, than the tables of "old" Part
20. Although rubidium-88 and cesium-138 (daughters of
krypton-88 and xenon-138, respectively) are not included in
"old" Part 20, they do need to be "considered separately
with regard to posting and other requirements..." of "old"
Part 20; the relevant concentrations for rubidium-88 and
cesium-138 are those listed at the end of Appendix B for
"Any single radionuclide not listed above with decay mode
other than alpha emission or spontaneous fission and with
radioactive half-life less than two hours." The "old" Part
20 does include the rubidium-87 daughter of krypton-87 and
the cesium-135 daughter of xenon-135, as well as many other
daughters whose parent radionuclides are listed in the
tables. Some very short-lived daughters of long-lived
radionuclides are not included in either "old" or "revised"
Part 20 (e.g., the 2.55-min barium-137m daughter of 30-year
cesium-137).
The tables in Appendix B of "old" and "revised" Part 20 are
consistent with respect to treatment of daughter
radionuclides in the dose modeling used to derive the ALIs
and DACs listed in the tables. When a listed radionuclide
has a radionuclide daughter, the value in the table for
that parent radionuclide takes into account the dose from
the daughter radionuclide produced in the body from the
decay of the parent following intake of the parent (unless
a "submersion" value is listed for the parent). However,
the value in the table for a parent radionuclide does not
take into account any simultaneous intake of the daughter
radionuclide. Thus the ALIs and DACs for daughter
radionuclides need "to be considered separately" from their
parent radionuclides "with regard to the posting and other
requirements of Part 20." (Reference: 10 CFR 20 Appendix
B).