Occupational Intakes of Radionuclides Part 1

Draft document: Occupational Intakes of Radionuclides Part 1
Submitted by Anthony Huffert, USNRC
Commenting on behalf of the organisation

USNRC Staff Comments

General Comments


1. The draft report should be separated into two main sections: one section should discuss changes from past ICRP recommendations and models, and the other section should be devoted exclusively to the new models, without any discussion of previous practices.  The draft report can be confusing because these two topics are interwoven throughout its contents, and therefore it does not clearly articulate the ICRP’s updated technical approach. Also, the extensive discussions on what changes will be made in the near future will be irrelevant after the series of documents are completed.  This separation would make the draft report easier to understand and make it a more useful reference for the future.


2. The draft report should clearly state if it will serve as the ICRP’s publication that will replace (update) ICRP Publications 54 and 78.  It is recognized that the ICRP plans to issue one or more CDs containing data useful for interpretation of bioassay measurements, but it is not clear from the draft report whether a new publication  dedicated to this topic is planned.  The ICRP should consider preparing a stand-alone document on this topic with companion CDs, so that it can serve as a useful reference.


3. The draft report contains information on model parameter values that serve as reference values that are not subject to uncertainty or assignment of error bands.   Although it is not feasible to provide uncertainty estimates for all other parameter values that do not serve as reference values, it would be useful to provide simple statistics concerning the data underlying certain key parameter values or default values. This information could be provided in an appendix to the draft report or a separate publication. 


Specific Comments   


4. Pages 8 to 23, lines 214 to 780: the Glossary introduces abbreviations of definitions that are traditionally used to designate something else.  For example, “MDA” is typically used to designate “minimum detectable activity,” but the draft report uses this term to designate the “minimum detectable amount.”  It is recommended that "MDQ"  (“minimum detectable quantity”) be used for the definition of the smallest true value of a measured quantity that is detectable by the measurement method.  The draft report should use ISO abbreviations and terminology for consistency.   


5. Page 10, lines 302 to 313: the term “Dose of Record” could be misinterpreted by radiation protection professional as the quantity that should be used for officially recording the effective dose of a worker exposed to external and/or internal sources of ionizing radiation.  Although it may be useful to have a quantity named for the external component of effective dose (based on personnel dosimetry), the term “Dose of Record” should be changed so that it is not interpreted for use in recordkeeping.


6. Page 26, line 857: The statement “the operational quantities for exposure to external radiation fields are directly measurable” should be expanded to state that effective dose is not an operational quantity and that the operational quantities are the ambient dose equivalent, the directional dose equivalent, and the personal dose equivalent, which are directly measureable.


7. Page 32, lines 1062 to 1095: this section should reference the more detailed discussion of the Human Respiratory Tract Model in section 3.2 (pages 48 to 78).


8. Page 34, lines 1177 and 1178: reference is made to ICRP Publication 107 providing nuclear decay data for radionuclides with half-lives greater than one minute, but there is no mention of ICRP developing dose coefficients for the same set of radionuclides.  In previous ICRP reports, tabulations of dose coefficients for intake of radionuclides by workers and member of the public were purposely limited to radionuclides with half-lives of 10 minutes or greater.  The draft report should state whether this approach will be used for the OIR series or whether an alternative cut-off will be used for developing dose coefficients.  It is recommended that ICRP develop dose coefficients for oxygen-15, nitrogen-13, and nitrogen-16, regardless of the half-life cut-off value used by ICRP for the OIR series.  


The following radionuclides have been identified as important for source security by the US Nuclear Regulatory Commission and the US Department of Energy: actinium-227,americium-241,americium-241/beryllium, californium-252, cobalt-60, curium-244,cesium-137, gadolinium-153, iridium-192, plutonium-238, plutonium-239/beryllium, polonium-210, promethium-147, radium-226, selenium-75, strontium-90, thorium-228, thorium-229, thulium-170, and ytterbium-169.   The ICRP should develop dose coefficients for each of these radionuclides, including those that emit neutrons. 


9. Page 38, lines 1335 to1338: this section of the draft report (section 1.8) should refer the reader to section 6.3.3 of the draft report (page 119, line 4241) for the ICRP reference that provides the rationale for using 5 micron AMAD as a default particle size for occupational settings.  It is recommended that section 6.3.3 provide statistical    distribution data for the 5 micron AMAD default value, explain why it was chosen for occupational settings, and why alternative default values (e.g. 1 micron AMAD) are used for environmental settings.


10. Page 41, line 1438: the committed effective dose (E(50)) does not indicate how to include dose from radionuclides absorbed through the skin.  This equation would be correct if the inhalation dose coefficients (ej,inh) for the applicable isotopes were adjusted (scaled) to account for the additional uptake through the skin.  Page 46, lines 1639 to 1640 identifies absorption and wounds as routes of uptake, but the remainder of the draft report provides little information on how the ICRP recommends accounting for it.  It is recommended that section 3.4 (pages 84 to 86, lines 2900 to 2991) should be expanded to provide information on assessing uptakes from skin absorption.  


11. Page 41, lines 1456 to 1462: the calculation of DAC is inconsistent with the definition of DAC on page 10, line 282 and the explanation of protection quantities on page 26, line 860, in that it uses a different breathing rate value.  Specifically, it is unclear why the DAC is defined for the Reference Worker (breathing rate of 1.2 m3h-1), but then calculated with a sex-averaged breathing rate (1.1 m3h-1).  Also, from these sections of the draft report, it is unclear when a sex-averaged breathing rate should be used.  It should clearly state whether default values associated with the Reference Worker incorporate the sex-averaging concept.  Also, it is recommended that the draft report provide additional information on Reference Person and Reference Worker and state under what circumstances each concept is applied.


12. Pages 52 to 62, lines 1822 to 2173: most of the experimental results obtained to derive particle retention and transport through the respiratory tract regions involved use of materials that are either of much lower density (e.g. polystyrene (1.05 g cm-3) and teflon (2.13 g cm-3)) or much higher density (e.g. gold (19.3 g cm-3)) than the average particle density assumed for aerosols in the Reference Worker exposure scenario (e.g. 3.00 g cm-3 per footnote “b” (lines 1785 to1788)). The draft report should explain how these experimental results were extrapolated to reflect an average density of 3.00.  Also, there should be an explanation of the shape factor used in experiments and the rationale for selection of a default shape factor of 1.5.     


13. Page 116, lines 4102 to 4140: a dose of 1 mSv is recommended as a level for licensees to consider taking more accurate dose assessments using site-specific data on aerosol characteristics.  It is recognized that dose coefficients with default parameters are intended to serve most occupational situations and all initial assessments, and that more refined assessments are appropriate to reduce uncertainties when there is the potential for elevated worker exposures.  However, the use of a prescriptive value such as 1 mSv is not recommended because licensees need flexibility for establishing their own dose level for more detailed assessments that are based on knowledge of their radiation safety program.  It is recommended that the numerical value of 1 mSv be replaced with a qualitative statement, such as “a significant fraction of the applicable radiation protection limits.”


14. Page 117, lines 4175 to 4177: a reference is made to the use of intake retention fraction tables, but there is insufficient detail about these tables throughout the draft report.  The draft report should state whether the ICRP plans to publish this information in future reports.

15.  Page 140: not all of the referenced documents are included in the Reference Section (e.g., Gerber and Thomas (1992) on page 97, line 3359; and Strom (2003) on page 118, line 4198).