|Health Physics and Environment (Technical Division in Atomic Energy Society of Japan) reviews gIndividualh document
Chairperson: Shigeo UCHIDA
The five foundation documents provide no replies to the numerous comments(200 reports)@submitted in response to the previous yearfs consultation (no replies are given in these documents). The ICRP should provide answers in a specific form, not in the form of the five foundation documents, at least to numerous common comments such as constraints and the concept of intervention. Holding an international conference to give an explanation about the results of the consultation for comments is crucial. The ICRP should make clear what parts of the documents have been changed and what parts are left unchanged in relation to the previous recommendations; and documents otherwise things will get mixed up.
Dose constraint to be compared with 95 percentile of the dose distribution in the case of compliances on derivation and monitoring of activity concentration for exemption and clearance.
The Commission recommends a guidance thatg the representative individual be identified such that the probability is less than about 5% that a person drawn at random from the hypothetical population will receive an annual dose exceeding the dose constraint. h To avoid any confusion of understanding for recommendation, especially in the case of exemption and clearance (including monitoring for compliances for clearance) for artificial radioactive nuclides, it should be clarified as an practical example in the text or new appendix that the dose constraint to be compared with 95 percentile of annual effective dose for public should be 0.1 mSv/y not a dose criteria of 0.01 mSv/y.
(Treatment in the ICRP 2005 draft report)
In the paragraph (S7) in the 2005 draft report of ICRP, a value of 0.01 mSv/y has been described as a minimum dose constraint. There is a following expression about dose constraint,g The Commission expects that the resulting national values of constraints will be lower than the maximum value recommended by the Commission, but probably not by as much as a factor of ten.h This would imply that the dose constraint for public in normal conditions should not be lower than 0.1 mSv/y which is one tenth of maximum dose constraint, 1 mSv/y.
(Treatment in IAEA: RS-G-1.7 and BSS)
In IAEA RS-G-1.7 hApplication of the concepts of exclusion, exemption and clearance (2004)h, the primary radiological basis for establishing values of activity concentration for the exemption of bulk amounts of material and for clearance was in that the effective doses to individuals should be of the order of 10 micro Sv or less in a year. In addition, to take account of the occurrence of low probability events leading to higher radiation exposures, an additional criterion was used, namely, the effective doses due to such low probability events should not exceed 1 mSv in a year. This approach is consistent with that used in establishing the values for exemption provided in Schedule I of the BSS.
(Treatment in ICRP Pub.46)
There are some descriptions about exemption in Pub. 46 gRadiation Protection Principles for the Disposal of Solid Radioactive Waste (1986).h
Studies of comparative risks experienced by the population in various activities appear to indicate that an annual probability of death of the order of 10-6 per year or less is not taken into account by individuals in their decisions as to actions that could influence their risks. Using rounded dose response factors for induced health effects, this level of risk corresponds to an annual dose of the order of 0.1 mSv.
Consideration should be given to the need for any optimization of radiation protection and to the possibility that many practices and sources of the same kind could combine now or in the future so that their total effect may be significant, even though each source causes an annual individual dose equivalent below 0.1 mSv to individuals in the critical group. This may involve assessments of dose commitments and of the collective dose per unit practice or source, in order to ensure that the individual dose requirement will not be exceeded now or in the future. It seems almost certain that the total annual dose to a single individual from exempted sources will be less than ten times the contribution from the exempted source giving the highest individual dose. This aspect could, therefore, be allowed for by reducing the annual individual dose exemption criterion from 0.1 to 0.01 mSv.
(Treatment in Pub. 82)
There are some descriptions about dose constraint and exemption in Pub. 82 gProtection of the Public in situations of prolonged radiation exposure (1999).h
The maximum value of the annual dose constraint to be used in the optimization of radiological protection for a single source should be less than 1 mSv in a year and a value of no more than about 0.3 mSv in a year would be appropriate.
Consideration should be given to exposure situations where combinations of transitory and prolonged exposure or a build-up over time of prolonged exposures from a source could occur. In these situations, it should be verified that appropriate dose assessment methods are used for ensuring compliance with the established dose constraint. The assessment should take account of any reasonably conceivable combination and build-up of exposures.
If, in a particular situation, such verification of compliance is not feasible, it would be prudent to restrict the prolonged component of the individual dose from the source with a dose constraint of the order of 0.1 mSv in any given year during the operational lifetime of the source.
The level of a trivial individual annual dose has been derived on the basis of risk-based considerations and also on considerations of natural background radiation. The level of annal risk which is held to be of no concern to individuals is taken to be around 10-6 to 10-7 and a trivial change in the natural background radiation is considered to be in the order of few percent of its average value of =~2.4 mSv per annum. Both considerations lead to an annual dose of the order of few hundreds of a millisievert.
(Linkage of the concepts of exemption and protection of public against prolonged exposure)
In Pub. 82, if appropriate dose assessment methods are not used and the assessment doesnft take account of any reasonably conceivable combination and build-up of exposures, the prolonged component of the individual dose from the source should be restricted with a dose constraint of the order of 0.1 mSv.
On the other hand, in Pub. 46, it can be recognized that consideration for exposure to different multiple sources makes the annual individual dose exemption criterion reduced from 0.1 to 0.01 mSv to assign the dose for a single source.
From the above interpretations of the recommendations, it would be deduced that the prolonged component of the individual dose from the exempted sources should be restrict with a dose constraint of the order of 0.1 mSv, because contribution of multiple exempted sources cannot be assessed using any appropriate dose assessment methods. This is consistent with the description in the ICRP 2005 draft report, gThe Commission expects that the resulting national values of constraints will be lower than the maximum value recommended by the Commission, but probably not by as much as a factor of ten.h(This would imply that the dose constraint for public in normal conditions should not be lower than 0.1 mSv/y which is one tenth of maximum dose constraint, 1 mSv/y.)
(Similar treatment in this fundamental document)
The guidance in this fundamental document requires reasonableness, sustainability and homogeneity in selecting characteristics of the representative individual. In particular, sustainability addresses the degree to which the selected characteristics can be continued over the time frame of the assessment. There are some examples about sustainability in paragraph 70 as follows;
It is inappropriate to assume, for example, that the same individual receives daily nutrient requirements independently from each of several different pathways (e.g., agriculture, and fishing). Also, it is inappropriate to assume that all foods consumed in an area are grown within that area if it is apparent that the location and land area available could not support the assumed dietary intake. Similarly, the intakes of wild game from an area should not exceed feasible game-capture rates.
From these viewpoints, it can be recognized that excess overlapped scenario is not appropriate and should not be considered in the assessment of representative individuals.
It can be concluded that especially in the case of exemption and clearance (including monitoring for compliances for clearance) for artificial radioactive nuclides, the dose constraint to be compared with 95 percentile of annual effective dose for public should be 0.1 mSv/y (a dose constraint for the prolonged component of the individual dose from the source when appropriate dose assessment methods are not used and the assessment doesnft take account of any reasonably conceivable combination and build-up of exposures) not a dose criterion of 0.01 mSv/y (annual individual dose exemption criterion obtained with consideration for exposure to different multiple sources and assignment of the dose due to a single source).