I would like to take this opportunity to supply comments to the draft report on Radiological Protection against Radon Exposure.
The draft document expands the recommendations of ICRP Publication 103 on radon-220.
I couldn’t agree more with the comments supplied by other colleagues that the vast majority of recommendations concern the radiation protection against exposures due to Rn-222 and, therefore, the document is unbalanced regarding Rn-220. It seems clear that the physical characteristics of Rn-220 and its short-lived decay products cause difficulties in the measurement and dose assessment. But when the Commission has the intention that Rn-220 shall be in the scope of the protection, implementation recommendations must be issued. Otherwise it could be happen that the protection against exposures due to Rn-220 will loose any meaning.
The draft document must be construed as meaning that the reference level of 10 mSv per year comprises now all exposures due to radon-222 and radon-220 from the different sources (soil, building materials and water). The reference level for the quantity activity concentration of radon-222 still remains at 300 Bq/m³. A corresponding value for radon-220 is missing. From that, a conflict may arise due to not keeping the dose reference level at the accounting of the individual contributions of the various exposures.
The accounting of various exposures from different sources (and pathways) is particularly important for setting priorities for the optimization and the dose assessment, especially for occupational exposures in NORM and other industries when relevant dose limits are to be kept (paragraph 3.4, 4.2, 4.3). The Commission must unambiguously clarify the accounting of various exposures.
Chapter 1.1, Background:
When radon-219 is not in the scope of this document, then Figure 2 is redundant. It could be also considered whether Figures 1 and 3 are dispensable for the document.
Paragraph 37, 56, 72:
Elevated exposures to indoor radon can be caused by the transport from the ground into the building and by exhalation of radon from building materials. The Commission recommends that indoor exposure is controllable since the pathway from the source to the exposed individuals can be controlled. It should be noted that the exhalation of radon from building materials can be controlled by source related provisions.
Paragraph 72, Justification:
The Commission brings forward the argument that the implementation of national radon protection strategies is justified because of the expected reduction of the detriment by radon (see bullets). Behind this argumentation a tautology conceals which prejudges the result of the justification process. It incapacitates the national authorities in carrying out the weighting of the reduced detriment with possible negative effects. The argumentation in this paragraph undermines the idea of the principle of justification. A prejudgement of the result should therefore be avoided.
Chapter 3.3, Optimization:
This chapter contains subchapters dealing with the reference level. One might get the impression that the setting up of the reference level is part of the optimization process. This is not the case. The optimization is an independent principle of the radiation protection aiming at reducing the exposures.
It is stated that the optimization process is source-related. This is in contradiction to the statement of paragraph 72 in which radon exposures can be controlled mainly by action modifying the pathways of exposure and normally not by acting directly on the source. See also paragraph 162 (line 1919-1920).
Paragraph 86 (line 1368 -1370), Paragraph 139 and 141:
ICRP adopted an individual dose level of 10 mSv per year as an upper value for the reference level for radon exposure. According to Publication 103 the Commission derived a reference level of 300 Bq/m³ for radon-222 in domestic dwellings as the protection quantity which involves a generalized occupancy time of 7000 h. In paragraph 86 it is stated that reference levels relate to the annual mean concentration of radon and paragraph 139 requires that radon measurements should be targeted to produce a reliable estimate of the long-term radon exposure of the occupants (taking into account many factors such as building occupancy and …). Paragraph 141 requires long-term measurements over the whole year….
The document lets the question open how the mutually overlapping effects of the individual behaviour and building characteristics be handled in practice. It is not clear whether the assessment of the exposures shall be carried out with a correction for the exposure conditions (considering the time of occupation) or not. In the first case the Commission must give hints how a correction is to be undertaken. This issue relates to the comparison of the measurement quantity (long-term measurement of activity concentration) with the protection quantity (in this case the reference level) which is not clearly elaborated in the draft document.
A long-term measurement over a whole year yields the average radon activity concentration at a special place irrespective of stay of persons. The conjunction to the individual dose is given by considering additional parameters (e.g. the time duration spent at this location).
It is well-known that the radon concentration in a room depends strongly from the conditions of usage of that room and the associated activity of persons. Investigations have clearly shown that the radon concentrations increase when the room is not occupied. Public buildings, for example, can have high concentrations during the weekend where no activities take place. The annual mean level given as activity concentration must, therefore, be clearly specified with respect to the treatment of times where the room or place is not occupied. Furthermore, the question arises how long-term measurements can be converted into a value of the average radon activity concentration under standard conditions of usage (airing behaviour to establish a minimum air exchange rate) in order to obtain a user-independent parameter for the radon ingress into the building.
This issue has to be taken into account when a legal regulation is implemented since persons who use this room or dwelling or any other location can not be completely released from their responsibility. In particular, this issue might be relevant when disputes between the owner of a dwelling and the tenant occur, because the individual condition of usage has effect on the proof of a successful optimization and, finally, the decision on further consequences. It will be in the interest of all parties to unambiguously clarify how a measurement is to be undertaken in order to prove that the reference value is kept.
Paragraph 92 must be clarified.
In contradiction to the statement in line 1733 construction materials can have a significant contribution to the overall exposure (depending on air ventilation rate). The current benchmark system (radioactive concentration index) seems to be not sufficient to control radon exhalation. Depending on the process of production (e.g. thermic or non-thermic) the radon exhalation rate can considerably vary even at the same gamma emission rate.
It is very important to note that all legal requirements to building materials become effective only for new buildings. New regulations will not affect building materials that have an approval by the competent authority and have already been used in existing buildings. In the latter case, building materials are hardly accessible for optimization. Regarding this issue the recommendations of the Commission don’t cover all relevant aspects.
For the sake of clarity it is recommended to focus the scope of the document on the radiological protection against radon in existing exposure situations. All parts of the document (paragraphs 3.4, 4.2 and 4.3) dealing with planned exposure situations should be removed or accordingly revised to outline the interface and the transfer from the existing to the planned exposure situation. Radon exposures in planned exposure situations are not treated sufficiently in the current draft document.