|Thank you for the opportunity to comment on the latest draft of the ICRP Recommendations. These are the views of the United Kingdom Ministry of Defence. Our comments are as follows:
This draft is much improved on the previous consultation document. In particular the ICRP principles of justification, optimisation and limitation are more prominent and ICRP is now reiterating the importance of optimisation in radiological protection, which has proved so successful, in reducing occupational radiation exposure. The sections on justification and optimisation are much clearer but we believe there should be greater separation between dose constraints and dose limits. The section on dose constraints should be reviewed to clarify what ICRP mean by dose constraint and to remove any ambiguity.
Chapter 2 - The aims and scope of the recommendations
Paragraph 29 Although it is recognised that ICRP is trying to use a new name for Deterministic Effects to better describe what they are, the use of the term “tissue reactions” is an unfortunate choice. While pre-cancerous changes may occur at the molecular level cancer is likely to be considered a particular manifestation of tissue disease. Thus the term “tissue reactions” has the potential for confusion with stochastic effects. Since a stated aim of the ICRP is to improve the presentation of the recommendations it is suggested that ICRP may wish to revisit the use of this new term. The description of stochastic effects as cancer/hereditary effects does provide a useful simplification.
Scope, exclusion and exemption
The treatment of these topics is indeed clearer compared with the text in the previous consultative draft. The removal of numerical values for exclusion levels from the recommendations is welcomed thus removing any potential conflict with other published values e.g. IAEA. However, (para 42) it should be possible to exclude a controllable dose at a trivial level from regulation in the same way as a non-controllable dose. ICRP proposed this in the consultative document titled The Scope of Radiological Protection Regulations. Therefore, it is suggested that ICRP should consider adopting this principle but leave the assignment of numerical values for radionuclides to others.
Paragraph 45 bullet 1 The document states “individual risk attributable to the radiation exposure caused by an exempted practice or an insignificant source (for man made sources, this is judged to correspond to an annual dose around 10 microsieverts.)” is one of the principles governing the process of exemption. In ICRP supporting publications the term used is a few tens of microsieverts. It would be helpful for consistency if a few tens of microsieverts could be adopted, or alternatively, if the document could clarify that say 20 microsieverts, which is used in UK, would be acceptable.
Paragraph 46 Should 10 microsieverts per year read a few tens of microsieverts per year or around 10 microsieverts per year for consistency with para 45. See previous comment.
Chapter 3 – Biological aspects of radiological protection
Paragraph 50 See the comment above (paragraph 45) on tissue reactions.
Paragraph 73 states the nominal risk coefficient for fatal cancer in the whole population. It would be helpful if ICRP could also add the nominal risk coefficient for fatal cancer in adult workers since this is useful in risk communication.
Chapter 4 – Dosimetric quantities
Paragraph 146 In use of the term collective effective dose it should not matter whether the radiation arises from natural sources or man-made sources, the principle should be the same. It is suggested that this statement made should include both sources of radiation. This could simply be achieved by deleting “natural”. This would make it consistent with paragraph 229.
Chapter 5 – The system of radiological protection of humans
Paragraphs 170 &171 The statement in paragraph 171 stating that other workers such as administrative staff and support staff, are more similar to the general public and treated as such does not fit well when it is placed at the end of a paragraph concerning workers in controlled areas. Administrative and support staff cannot be treated as members of the public since as employees they have rights and duties, which members of the public cannot have.
Para 171 ICRP recognises workers who work in controlled areas and other workers such as administrative and support staff but there is an additional class of worker who works with radiation but not in a controlled area. Examples include workers who operate baggage and postal search machines and dental staff. Does ICRP wish to make a statement about such workers?
Principle of justification
The treatment of the principle of justification is considered to be much clearer than in the previous consultative document.
Principle of optimisation
The increased prominence of the principle of optimisation in this consultative document compared with the earlier consultative document is welcomed. The principle of optimisation has served to reduce significantly worker radiation exposure and the concern that we expressed previously that ALARA was in danger of being undermined by increased emphasis on source related constraints has now been addressed.
Dose constraints have traditionally been applied as a source related restriction for prospective exposures and as a starting point in the optimisation process. Figure 2 allows the interpretation of a dose constraint as a pseudo dose limit for normal, emergency or existing controllable situations for single sources. The figure makes no reference to it being prospective dose. Therefore it would be useful for ICRP to explain that dose constraints are only to be used for prospective exposures and are not to be used as pseudo dose limits for single sources unless it is ICRP’s intention to extend the role of dose constraints.
Given the caveat that equivalent dose should not be used in lieu of absorbed dose for deterministic effects, the unit Sv is used in the context of serious and tissue injuries at paragraph 213 and deterministic health effects at paragraph 326. This should read Gy.
On the subject of limitations on the use of collective dose, the first sentence of paragraph 229 is strongly supported by the UK Ministry of Defence and we would wish to see it carried forward into the publication of ICRP’s recommendations. It would be helpful for ICRP to give some indication of what is meant by long time periods.
In paragraph 239 it states that “intakes may be averaged over a period of 5 years” while in paragraph 128 states that committed dose is assigned to the year in which the intake occurred. They appear to be conflicting statements. It is suggested that ICRP resolve or explain these inconsistencies.
Natural sources of radiation
Subject to the comments relating to chapter 7 below the treatment of natural sources of radiations by the ICRP is considered adequate in this present draft.
Chapter 7 – Exposure to natural sources
Paragraph 295 This paragraph states that “the fact that sources that are feasible to control but deliver such small exposures that control is unjustified or unnecessary and should be exempted from most of the requirements of the radiation protection system.” This is a recommendation, which is applicable across the whole of radiological protection and therefore should be moved elsewhere such as in the chapter titled the system of radiological protection for humans to be universally applicable.
Paragraphs 301-303 If a constraint for radon is expressed in terms of activity concentration, the calculation from the fundamental 10mSv constraint is made using assumptions about the degree of disequilibrium in the workplace (probably around 0.4 – 0.5). This will be far from the case in many underground workplaces especially if there is forced ventilation, where disequilibrium may be <0.1, and the constraint expressed in terms of activity concentration of radon will be far too pessimistic. Hence there should be a caveat to this statement.
Chapter 8 – Potential exposures
Paragraph 326. Please see earlier comment (paragraph 213) referring to the use of Sv for serious and tissue injuries.
Chapter 10 – Protection of the environment
Paragraph 351 The inclusion of protection of the environment is questioned. Are there sufficient similarities between plant and animal species to use the reference plant and animal logarithmic bands of dose rates and endpoints and be able to apply this to all other plants and animals? The achievement of the criteria, or not, should be a decision point as to whether to continue with, modify or cease to use the concept. If its inclusion were delayed until the next round of ICRP recommendations (circa 2020) this would provide sufficient time to achieve a larger knowledge base and a better understanding of whether the ICRP view that the standards of environmental control needed to protect man to the degree currently thought desirable will ensure that other species are not put at risk is correct.
Paragraph 228 “…. concerned group of individuals” is unfortunate phraseology it should read “the group of individuals concerned”.