2005 ICRP Recommendation

Draft document: 2005 ICRP Recommendation
Submitted by Staff of the NRPB, National Radiological Protection Board
Commenting on behalf of the organisation

PART 4 9. ICRP Draft Section 6 - The Commission’s required level of protection for individuals The ideas in this section need to be further developed and clarified to support and explain the choice of source-related individual dose constraints. No reasons are given in terms of the associated risk (as in Publication 60), whether absolute or relative to other activities, for the judgements as to what are acceptable dose levels. Surely some support should be given for the decisions which are made, other than reference to the average annual natural background effective dose? For example, it is surprising that lifetime risk does not influence the choice of dose constraints. It is important that if new concepts such as ‘age-averaged effective dose coefficients’ are introduced their use and application is fully explained. It should be clearly stated that the dose limits and constraints apply to the sum of the external irradiation dose received in a year and the internal radiation dose from intakes in the year. The continuity with ICRP publication 65 is welcomed and supported. The factors which moulded the form of Publication 65 still apply. Radon exposures are very variable from country to country. They are often much higher than would be wished. They are controllable, but particularly in the case of exposures in existing dwellings, at a potentially huge cost. They are not a new mode of exposure and public attitudes are not the same as to doses from nuclear power. The recommendations of ICRP 65 had a strong element of flexibility and pragmatism. The advice was intended to help national authorities define a manageable radon problem in dwellings so that the worst exposures could be tackled. Occupational exposures were being brought into the system of control for the first time. It was accepted that the existing philosophy would be stretched in accommodating this new and very different class of exposures. The new recommendations on radon are brief. Perhaps for this reason, the continuity with ICRP 65 is sometimes not obvious and the sense of pragmatism is no longer apparent. Rather there is a sense that radon policy follows inexorably from the system of protection. In particular, the draft recommendations could be read as overly dogmatic on the question of the lower end of the range in which Action Levels should be set and on prohibiting reduction of radon levels below the Action Level. No strong arguments are advanced on these points. It would be better to avoid these recommendations. Table 7 gives detailed technical comments on Section 6 of the ICRP draft report. TABLE 7 Technical comments on the Commission’s required levels of protection for individuals 156 As noted in the General Comments above, it is not clear why or how the Commission is strengthening its previous recommendations. Last sentence should perhaps end with – “…apart from medical exposures of patients”. 159 The second sentence should make clear that it is referring to annual dose. Having said that, 100 mSv per year, in almost all cases, would represent a drastic lowering of protection standards. The issue of manned space flights is not straightforward, particularly the justification for space tourism, and may not be a good example here. 160 The suggestion that doses of several tens of mSv “require that action be considered” is remarkably weak in terms of comparisons with current practice. Again, it suggests a lowering of protection standards. Furthermore, there is insufficient distinction between the actions required for these exposures and those required for doses “within the natural background range”. In fact this whole paragraph is problematic when compared with current practice. 161 The meaning of the first sentence is very unclear. The phrase about practices that “have not been judged to be frivolous” appears to relate to justification, albeit in an undefined way. More explanation of this phrase is needed. 162 The suggestion that the maximum dose constraints are consistent with previous decisions is not as apparent as the Commission suggests. Specifically, the relationship between dose limits and (maximum) dose constraints is still rather confusing. The meaning of the last sentence of paragraph 162 is very unclear. 163 Table 7 does not just present ‘maximum’ values – three are maximums but one is a minimum value. As stated previously the retention of the dose limits with the same numerical values as the maximum value of the dose constraint needs to be addressed. It is agreed that actual dose constraints will have to be lower, but there is a real need for more guidance than is provided by the last sentence. For example, what are the criteria for selecting dose constraints? Where does the factor of 10 come from? 164 The first bullet point (emergencies) refers to a 100 mSv constraint, which suggests that (in theory) total doses could be higher, ie, due to emergencies involving different sources. In practice, of course, the dose is received from a single practice or source, and dose limits are the main consideration. It does not seem to be wholly correct to say that there cannot be societal benefits above this dose. Also, it is not clear what the last sentence (in the first bullet point) is saying. In the second bullet point (20 mSv maximum dose constraint), essentially the same arguments apply, ie, in practice there is one source and dose limits (plus optimisation) already provide sufficient protection. The 1 mSv/y dose constraint appears to add nothing to current practice. The 0.01 mSv/y minimum constraint needs further explanation, since such level of dose cannot be reliably assessed in most circumstances. Examples of how/when this constraint should be used would be helpful. In the final bullet point of paragraph 164 it refers to publication 77 and a constraint of 0.3 mSv/y, this needs clarification. 165 This suggests that the constraint for one source is influenced by the number of other sources that persons are exposed to. Although this may be inevitable when (total) exposures are close to dose limits, in most occupational exposure situations this is not the case. In such situations, the dose constraint for one source is surely unconnected with the number of sources present. 166 This paragraph refers to practical protection, but still fails to provide any information on what a dose constraint actually represents and how a value should be determined in practice. It is suggested that an example would be very useful. 168 Comforters and carers of patients are not “patients” they are “informed individuals”. If ICRP’s definition of “medical exposure” is still to include exposure of such comforters and carers, this type of individual (“informed”) can undergo both “occupational” and “medical” exposures, contrary to the second sentence of this paragraph. 168-184 Explicit reference to where emergency responders fit in these recommendations would be helpful. 169 It seems a good idea to treat some workers as members of the public but does this need further discussion and clarification? The Commission should avoid the use of the phrase “controlled areas”, especially in quotation marks, in this paragraph. 170 If the reference to comforters and carers is to be retained, the heading of this paragraph should be simply “Medical exposure”. Some confusion between those comforting patients and general members of the public could be avoided by referring to the former as “Friends and relatives supporting patients …” at the beginning of the 3rd sentence and to the latter as “… for general members of the public.” at the end of the 4th sentence. The reference at end of the paragraph should be to Section 9.4 (not Section 9.3). 172 NRPB welcomes the retention of the critical group concept, which has proved valuable over many years. However, there is the need for clarification of the concept and guidance on the issue of homogeneity. Guidance is also required on what is meant by a ‘sustainable group’. 173 The introduction of “age-averaged dose coefficients” is a major change to the system of protection and more information is required to judge whether it is appropriate. It is vital that the document being developed by the Task Group of ICRP Committee 4 is made available for comment. The use of age-averaged dose coefficients has the potential to have an impact that would extend to emergency planning and response. For example uniformity of application of ERLs across population groups. This would not be highly desirable in the emergencies field. 175 “…additional controls have to be considered to protect the unborn child.” Suggest replace have to be with should. It is assumed here that protection of the mother will protect the fetus prior to the declaration of pregnancy and that additional protection may then be necessary. This omits consideration of work with particular radionuclides for which early declaration of pregnancy might be encouraged. 176 Last sentence: “The Commission is developing guidance for the restriction of intakes to breast-feeding mothers in a report from ICRP Committee 2.” The report will give dose coefficients and include some discussion but not guidance. 177 “For members of the public the limit on effective dose means that the embryo/fetus is adequately protected and no further restrictions are recommended.” In fact, the dose to the fetus can be substantially greater than the mother’s dose for intakes of particular radionuclides. 179 The recommended lower limits for Action Levels are above those which several countries have, in practice, selected. It seems undesirable for the Commission to insist on a recommendation which is not followed unless there are very powerful reasons for it. The rationale of ICRP 65 for suggesting a lower limit for the domestic Action Level of 200 Bq m-3 was that it equated to 3 mSv and that a lower Action level would equate to a dose below that from natural background sources (para 72). The range of action levels for workplaces was chosen to give the same range of doses as that in dwellings (para 86). In many countries the mean dose from natural background is below 3 mSv (less than half this in the UK, using the ICRP conversion convention for radon). Many people will also be unconvinced that the level of natural background should provide a limit for doses from controllable sources. We suggest the removal of both occurrences of “no less than” in the last sentence of paragraph 179 and the addition of a sentence along the lines of: “The Commission accepts that, where national considerations so indicate, an Action Level may be set below this suggested range” 180 Although the Commission’s application of the recommended system of constraints is quite clearly laid out here, there does appear to be an inherent gap in the logic. Specifically, the basis of the constraints system (eg, as illustrated in Figure 3) is based on multiples of background excluding radon. It does then seem rather illogical to base radon action levels on these criteria, when in fact the concept of controllability is really a function of radon background levels. The intention may be that the final sentences should be read as recommending that no regulatory campaigns should be directed at dwellings or workplaces below the respective Action Levels. This would be fine. But they could be read as recommending that any remedial action should be limited to reducing radon concentrations to just below the Action Level. This is not the advice of Publication 65 which says, quite explicitly (paragraph 71) “It is important that the action taken should be intended to produce substantial reduction in radon exposures. It is not sufficient to adopt marginal improvements aimed only at reducing the radon concentrations to a value just below the Action Level”. The best option might be to re-iterate these sentences in the new recommendations. The new recommendations should also note that advice given relates to existing dwellings and workplaces and that radon preventative measures in new buildings are very cost effective. 183 and 184 When referring to arguments developed in ICRP 60 it is important to make it clear whether the Commission think that they still apply. 185 Again it is important to deal with the fact that the dose limit and the maximum value of the dose constraint are the same numerically. Here it refers to “the use of constraints on single sources which are more restrictive than limits in normal situations”, which is confusing. Is there a case for dropping the averaging over 5 years for public exposure as it is rarely applied? 10. ICRP Draft Section 7 - The optimisation of protection This section again requires further clarification and it is hard to comment on some of the concepts without seeing the ICRP Committee 4 Foundation document. NRPB supports the retention of the concept of collective dose and agrees that it is not appropriate to simply estimate the full collective dose commitment integrated over all space and time. However, the idea of a ‘matrix’ needs clarification and it is important to recognise that there are practical limitations to what can be calculated. There is nothing in Section 7 to indicate that optimisation should be applied to the protection of patients as well as to the protection of members of the public and workers. Detailed technical comments on this section of the ICRP draft recommendations are given in Table 8. TABLE 8 Technical comments on the Optimisation of protection 189 The phrase “tend to” is much too weak, and these words could in fact be deleted. 190 The first sentence could be seen as rather misleading. Of course, it is only possible to reduce future doses. However, optimisation, in practice also involves retrospective analysis, eg, of previous doses, existing control measures, etc. The phrase “Questioning whether the best has been done …” is open to misinterpretation, and it should be clarified to indicate that it is the best overall solution, ie, not just the lowest dose solution. 191 The message of this paragraph is unclear. 194 and 195 These paragraphs leave the impression that it is important to get exposures down as low as you possibly can and it is not clear how optimisation comes into the decision. It would be helpful if ICRP could clarify what should happen at doses below the minimum value of any constraint (0.01 mSv/y). Is reduction below these doses still desirable? 195 The basic role of optimisation is to restrict exposures. Safety culture is often an important, in some cases essential, factor in achieving this. But it is not the main role of optimisation. 198 It is important to recognise that although this is the definition of collective dose it is not possible to calculate collective doses this way in practice. For estimating doses from consumption of radioactivity in food account has to be taken of the fact that people do not obtain their food from where they live. For both aquatic and terrestrial foods collective doses are estimated based on distributions of the production of the food and do not give information on who eats the food. It is not therefore possible to obtain information on the breakdown of the collective dose into the contributing individual doses. The timescales of collective dose are also generally longer than individual lifetimes which further complicates the issue. 201 As discussed above it is not possible to provide a distribution of individual doses as envisaged here. The most that would be possible is to provide information on “per-caput doses”, ie, the collective dose divided by the exposed population. This can be done using the collective dose truncated at relevant times or using collective dose rates. The complicated optimisation process using different weightings for components of the dose matrix seems at variance with the idea of a more qualitative system discussed in paragraphs 194 and 195. 202 This needs further thought and development. As stated above the magnitude of individual doses and the number of exposed individuals can not always be known. It is overly complicated to take account of age and gender dependent risks and this contradicts earlier sections of the recommendations that said these did not need to be taken into account. It would be better to recommend that the collective dose is broken down by geographical region and time and that some indication is given of the levels of individual dose involved. A full radiological impact assessment would also include an estimate of critical group doses. 11. ICRP Draft Section 8 - Exclusion of sources from the scope of the recommendations It would be helpful if this section could repeat the discussion on the difference between exclusion and exemption and as in paragraph 25 state that national authorities can set exemption levels higher than the exclusion values in Table 10. Table 9 of this report gives detailed comments on Section 8 of the ICRP draft recommendations. TABLE 9 Technical comments on the exclusion of sources from the scope of the recommendations 206 The Commission’s approach seems too simplistic, given that radionuclide specific exemption levels have already been derived (eg, IAEA and EC BSS), and are in widespread use already. 208 The phrase “only conceivable actions” is too sweeping, and technically incorrect – other actions are at least conceivable. Disruption and the need for considerable resources are not arguments in themselves. There should also be considerations of controllability (exclusion) or limited risk (exemption). Also see earlier comments on S12. Table 10 There are a number of significant omissions from this Table, notably tritium and carbon-14, which occur naturally but can also be produced artificially, and uranium-235. It is also not clear what the adoption of an exclusion activity concentration for 40K will achieve. Pure natural potassium contains about 30 Bq/g and does not pose any significant hazard. This is because internal exposures to 40K are homoeostatically controlled so that the activity concentration is irrelevant, and the external dose from pure potassium is very low and is unlikely to warrant any controls. 211 and 212 These paragraphs are useful and help clarify the situations. The clear statement on exposure of air passengers to cosmic radiation is welcome and helpful.