|NDAWG comments on ICRP foundation documents
The National Dose Assessment Working Group (NDAWG) was established in the UK in 2002. The aim of NDAWG is to bring together people and organisations with responsibility for, and/or an interest in, the assessment of radiation doses from the operation of the nuclear industry and from minor users of radioactivity. Further information on the work of NDAWG, including the current membership, is available on the website, www.ndawg.org.
Members of NDAWG have considered the draft Foundation document of the International Commission on Radiological Protection (ICRP) as published on the ICRP website. The following set of comments represent the views of the majority of members but not necessarily the organisations that they represent.
The Optimisation of Radiological Protection: Broadening the Process
NDAWG members feel that the discussion in this paper is so general that it is hard to disagree with it but equally hard to draw any real guidance, let alone recommendations, from it.
The annexes on the application of optimisation do not illustrate how the key problem of combining quantitative and qualitative inputs in making specific decisions can be achieved, and read rather like a summation of historical experience and best practice in radiological control.
The paper would be much improved if it were possible to incorporate some real, or even hypothetical, case studies which show how the principles and philosophy discussed can be applied to real and specific decisions.
The document suggests ways in which disaggregation of collective doses could be done but gives no real guidance as to how the results should be used. It is important to recognise that although the definition of collective dose is as given, collective doses for the public are not usually calculated 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 often 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 accurate information on the breakdown of the collective dose into the contributing individual doses. The timescales of collective dose estimation are also generally longer than individual lifetimes which further complicates the issue.
The emphasis on distinguishing between exposed groups on the basis of age and gender seems to contradict the discussion on averaged effective dose in Section 5.5 of the Committee 2 Foundation report on dosimetric quantities. As reference values are used to estimate effective doses, which are averaged over both sexes, it does not seem consistent to then talk about distinguishing between different group by gender.
NDAWG members agree with the conclusions of the document that optimisation of doses is more than a simple mathematical process and that a simple utilitarian approach to the optimisation/distribution of dose would not be acceptable. Factors such as equality between different groups and intergenerational equity also need to be taken account of.
Specific comments on the text:
Page 4 (Abstract), It is agreed that groups of exposed individuals can usefully be characterised by attributes such as age, gender and habits and/or by exposure characteristics, including statistical measures of the distribution of doses within the group. Multiple such groups could be considered in the optimisation of protection for a source. However, it should be recognised that in many cases it is not practical to distinguish by gender and/or age.
Page 19, It would help to say that it may not be necessary or practical to take account of this lengthy list of attributes. It should be made clear that the key concern is the sensitivity of the embryo/foetus and not the pregnant woman. Under social considerations and values, it is not clear whether there is a distinction between equity and fairness.
Para 39. This begins by talking about environmental actions, this does not relate to the remainder of the paragraph which discusses source-related controls.
Paras 64. The mention of the word "summing" implies a particular approach to collective dose. It is not however estimated that way, and any such implication should be removed.
Para 71. Why should optimisation be focused on a single exposure pathway? Surely all pathways should be considered, at least initially. Source-related optimisation may well affect more than one pathway.
Para. 73, The suggestion that different weightings are applied to the doses received by different elements of the dose matrix could be seen to imply that the dose received by members of one group was not as important as that received by members of another group. This would not be defensible.
Annex 2 on public exposure. Much of this relates to individual dose, which is contrary to the approach based on sub-collective doses given in the main text. The Annex would benefit from less discussion and more in the way of practical guidance.
Page 35, A dose constraint of 1 mSv/y is proposed when a single source contributes the principal route of exposure. However, this does not include contributions to doses from discharges in earlier years. One might therefore have expected a value below 1 mSv, or a suitable comment about historical discharges.
Page 39, For accidents and long-term contamination, a dose constraint of 20 mSv/y is suggested. Is this not inconsistent with the 10 mSv value used for prolonged exposures?
Page 44, Some additional comment is required to explain what is meant by ‘not entailing excessive cost’ in terms of the value of impact reduction compared with the resources used in emission reduction.
Page 46, The bullet point relating to half lives of radionuclides is rather confused and does not recognise that long-lived radionuclides may have a short environmental persistence or, conversely, that short-lived radionuclides may be sustained by long-lived progenitors. It is felt that the discussion of radionuclides confuses the more general point on distribution of doses that is being made.