|The ICRP draft report has been reviewed by a working group in the Central Research Institute of Electric Power Industry (CRIEPI).
1. General comments
It is necessary to carefully elaborate the draft so that each sentence could be uniquely interpreted. For example, the issue who should determine dose constraints is very important for the parties involved in radiation protection such as the regulatory authority and operators in each country. However, the additional guidance (Paragraphs (211)-(220)) on the selection of constraints for occupational, medical and public exposures in three exposures types, could be interpreted differently and have generated much controversy. The issues of single source and Table 4 are also ambiguous.
It is necessary to carefully modify the draft to clearly distinguish flexibility that each country can set by oneself and ambiguity of expression. It is the basic and essential principles for drawing up any documents that each sentence, figure and table (e.g., Table 4) should have only one meaning. ICRP should publish the recommendation only after these principles are fulfilled.
2. Specific comments
(1) Dose constraint for occupational exposure
·Paragraphs (187), (209)-(212) and Table 4
Although the concept of dose constraint is understandable, it should be clearly stated that the numerical value of dose constraint is determined voluntarily by each operator.
Paragraph (187) states that for occupational exposure, dose limits apply to the situations determined by the regulator. In contrast, paragraphs (211) and (212), which state the dose constraint for occupational exposure, can be interpreted to mean that the use of the dose constraint rather than the dose limit is recommended. The use of the dose limit and dose constraint for occupational exposure is not clearly established.
Regarding workers at nuclear power plants who are classified under the occupational exposure group, the doses of all workers in Japan are managed as an integrated dose and controlled as a result of individual monitoring. Therefore, the government and regulatory authority should determine dose limits as before and it is not necessary to set dose constraints. The intention that each operator voluntarily sets dose constraints should be stated clearly.
(2) Dose constraint for public exposure in planned situations
·Paragraphs (216)-(217) and Table 4
The concept of the dose constraint is understandable; however, it should be clearly stated that the selection of 1 mSv/y as the dose constraint, which is the same as the dose limit, is possible if we consider the conservative nature of “case-by-case dose assessment results.”
When considering the use of the dose constraint for public exposure, ICRP should carefully consider practical techniques to be used for prospective dose assessment. For example, in calculating derived levels that will be applied to facilities throughout Japan (e.g., gaseous and liquid radioactivity concentration limits in exhaust air and water), because data are calculated from the results obtained from all facilities using radioactive materials, conservative conditions are adopted such as the public drinking discharged waste water without dilution or the public inhaling gaseous waste from a facility with the same concentration as that measured at the border of a premise without dilution. Currently, in Japan, results of the above-mentioned dose assessment are compared with the dose limit for the public in order to calculate the derived levels. This kind of conservative measure enables us to impose an identical regulation on all facilities and simplifies the regulatory system. Furthermore, this eliminates the detailed assessment of individual facilities, leading to benefits for both the regulatory authority and operators because of burden reduction.
Adopting a dose constraint lower than the dose limit to comply with the limit for the public is an attempt to improve the accuracy of the standard. However, the standard (dose constraint) becomes stricter as a result. Thus, for example, the above-mentioned comprehensible and most conservative assessment method cannot be used to demonstrate that a conventional radiation protection measure is usable. It is necessary to carry out accurate dose assessment specific to each facility. In reality, it will be necessary to prove that far lower dose assessment results can be obtained. Accordingly, for example, to calculate the derived level for an entire country, more accurate dose assessment for all individual radiation facilities will be required. If a conclusion that a derived level specific to each facility is reasonably necessary, not only the regulatory system becomes complex, but also dose-assessment-related examination and application workloads increase for the regulatory authority and operators, respectively, leading to disadvantages.
·Paragraphs (57) and (146)-(148)
Numerical value should be given to define the very low dose range that should not be included in the evaluation of collective dose (e.g., a few mSv or less).
In the document, it is stated that it is inappropriate to calculate the number of hypothetical cases of cancer or heritable diseases on the basis of collective dose data obtained from a large number of people who received very low dose exposures. In addition, it is also stated that some restrictive conditions should be imposed on the evaluation of collective doses; i.e., the range of dose and period should be specified. These are synonymous to saying that the LNT hypothesis is not adopted in the very low dose range. We should remember the argument that led to the statement that the linearity of risk is limited to the dose range higher than “a few mSv” (ICRP, The evolution of the system of radiological protection: The justification for new ICRP recommendations, J. Radiol. Prot. 23, 129-142 (2003), Table 4). The lower applicable range for the collective dose and LNT hypothesis (e.g., few mSv) should be clearly specified on the basis of the background level due to natural radiation.
·Paragraph (230) should be deleted.
The ICRP recommendation should be used for radiation protection, but not as a guide for epidemiology. We should not make suggestions as if the collective dose is usable in epidemiological studies by citing a special case. This has already been stated in sections 3.2.1 and 4.5.7. It is important to emphasize this, but it is not necessary to repeat this here.
·Paragraphs (55), (57)
“Scientific” should be deleted.
It is stated that for the purposes of radiological protection, LNT is scientifically reasonable... or scientifically plausible; however, LNT is a hypothesis introduced for radiation management for practical purposes. LNT is not a hypothesis based on scientific evidence; thus, the word “scientifically” is not appropriate.
The exemption principle should be stated accurately.
In the recommendation published in 1990 and the draft published in 2005, no expression on numerical values for exemption is included. Concrete numerical values are indicated in IAEA and other publications. On the other hand, in this recommendation, numerical values are given using an inaccurate expression as “around 10 micro Sv.” If numerical values are included in this recommendation, an accurate expression as “of the order of 10 micro Sv or less than” should be used on the basis of the expressions in ICRP Pub. 46 and IAEA BSS. Moreover, thus far, in both ICRP Pub. 46 and IAEA BSS, 1 man.Sv is adopted as the exemption criteria for not only individual dose but also collective doses. In this recommendation, the validity of collective dose calculated by summing very low doses that can be exempted from regulation is clearly contradicted. Therefore, it should be clearly stated that the collective dose of 1 man.Sv is not required as the criteria for exemption from now on.
·Paragraphs (152), (154)
Uncertainty should be allowed for future dose assessment.
Probability-based assessment is applicable for future dose assessment; the basic idea is put together in the foundation document “Assessing Dose of the Representative Individual for Radiation Protection of the Public” (to be published as Pub. 101). In this document, it is stated that it is appropriate to consider the concept of uncertainty in dose assessment to determine whether the current dose exceeds the previous dose limit and that the concept of uncertainty need not be considered in future dose assessment models and parameters. However, it does not reflect the idea of probability-based dose assessment, which is adopted in the foundation document related to the “Representative Individual.”