|Comments on the ICRP foundation document draft: The Optimization of Radiological Protection by the working group on the implications of ICRP draft documents (chairperson : Dr. Kenzo Fujimoto), National Institute of Radiological Sciences, JAPAN.
Optimization document is reviewed by Drs.R. Kanda, Y. Yamada, Y. Yonehara, A. Furukawa and M. Doi.
Evolution of the concept
1. Evolution of the optimization concepts in the ICRP recommendations has been reviewed in paragraphs 10 to 17, which should be reviewed with the evolution of the comprehensive system of radiation protection, together with the justification of the practice and individual dose limitation. Evolutions of the indexes of harm should also be reviewed in the context of individual risk estimation concerning individual attributes that lead to the evolutions of the system of radiation protection.
2. Optimization of the protection is the concept that should be discussed in the context of the system of radiation protection.
3. Essentially, the optimization of the protection is the multi-attributable issues, and an objective function should be identified to make balancing of the resources for the protection or scoring and ranking of multiple factors.
4. "Best available protection", or "the best protection option under the prevailing circumstances (BAT) " in the draft should be distinguished clearly from the former optimization concept in Publication 55 (1988) as shown in chapter 16, i.e., the level of protection so as to Òobtain the best that can be achieved in the circumstancesÓ.
5. As also shown in page 44, both ALARA and BAT are moving targets. If BAT is much concerned on the emission of radioactivity to the environment, and its potential impacts on public health and environment, discussion of BAT should be detached from the ALARA, that considers health effects of radiation exposures to workers.
6. Although optimization of protection in Publication 82 (1999) is reviewed in page 14, it must be emphasized that the protection level in the recommendation is prepared for the public from the prolonged exposure situations by the sources in the environment. It should be decided by taking attributes into accounts regarding not only the radiation protection issues but also the other social and economical issues in order to handle with the sources in prolonged situation for the protection of the public. Participatory democracy would also be required as a stakeholder involvement process in these cases, and BAT should be discussed taking precautionary principle into consideration. While, these cases should be distinguished from the ALARA cases which decides the optimum protection level of workers.
7. Paragraph 24, in page 15: Optimization of radiation protection including NORM should be a issue of Òmultiple sourcesÓ. Since massive NORM are widely used, we should take multiple exposures from NORM as well as specific artificial sources. Pragmatic principles of optimization for regulating the multiple massive sources should be discussed. NORM that exceeds the exclusion level, should be considered independently as massive sources, and the (maximum) dose constraint should be shared to each source. Or, we should develop the comprehensive optimization procedures designed for "the optimization of muitiple sources". The process of setting the dose constraints for multiple sources should be discussed with consideration of the individual dose limit and maximum dose constraints for the levels of concern.@
8. In page 17, paragraph 28, the role of the optimization is to foster a safety culture, which should make everyone responsible for the radiation protection to remind repeatedly, "the current level of protection is reasonable to avoid useless doses and reduce unnecessary doses properly?". This should be a feedback process, as imaged in Figure 2. Feedback and check circulation is an important unique aspect of the proposal, and should be emphasized.
9. Figure 1 is well designed, and qualitatively, it gives us a fair idea of optimization, and relationships between constraints and optimum levels for each situations. But, the values of dose constraints (maximum constraints) for 3 situations should be different so that the figure may cause confusions and misunderstanding for the stakeholders who may see only the figure since 0.01 mSv/y, 1 mSv/y, 20 mSv/y and 100 mSv/y are the proposed constraints in the draft of 2005 recommendations. For each situations, the constraint levels (maximum constraints) should be identified quantitatively. For example, in the figure of "planned situation": constraint (maximum constraint) for workers: 20 mSv/y, for public: 1 mSv/y.
10. In Figure 1, time courses of the dose and the levels (constraint, authorized level, intervention level) are not distinctive. Time courses should be shown by the bold line, and the levels should be shown by the dotted line.
11. In Figure 1, we understand that the intervention level is the minimum dose level above which the interventional countermeasure should be exercised. If so, the dose level achieved as the result of optimization should be equal to or less than the intervention level. It will be appreciated if the concept of intervention is defined clearly.
12. In the bottom of Figure 1 (controllable existing situations), a point of time when intervention is introduced should be added.
13. Paragraph 24, in page 15: Optimization of radiation protection including NORM should be a issue of "multiple sources", since massive NORM are widely used in our daily lives, and we have exposures from multiple natural sources (NORM) as well as specific artificial ones. Pragmatic principles of optimization for regulating the multiple massive sources should be discussed. NORM (that exceeds the exclusion level) should be considered independently as massive sources, and the (maximum) dose constraint should be shared to each source. Or, we should develop the comprehensive optimization procedures designed for "the optimization of multiple sources". The process of setting the (maximum) dose constraints for each multiple sources should be considered in connection to the individual dose limit and optimization.@
14. In page 23 and 24, stakeholder involvement is discussed. Participatory democracy with transparency and openness is truly important as a process to involve many parties and individuals who have concerns on the radiation protection. And as well, it is also important to define clearly the responsibility of the decision makers (regulators and operators). Stakeholder involvement is a process which should carefully been reviewed and respected by the decision makers. While, the stakeholder involvement is not only for the decision making process. This should be emphasized in the draft repeatedly.
15. The role of specialists in the stakeholder involvement is not clear in the draft. Should we, specialists behave as outsiders, and just to answer the queries of the stakeholders objectively without mentioning our opinions? Or, should we participate in the process as members of stakeholders, who are responsible for the risk management of radiation?
16. Paragraph 53 says there is no unique approach for stakeholder involvement. And it also says that the wide spectrum from the one end to the other, covering classical consultation process and well-established consensus formulation process. Actually, it should be case by case, and there is no generic Òhow toÓ for developing stakeholder discussions. However, international and national harmonization might need the requirement of local stakeholder to harmonize with the international and national common policies and compliances. In case of the discharge of radioactive materials, consequences should be shared internationally and nationally, and the above gap should be filled by the common procedure that allows local flexibility to a certain extent.
P.16, Figure 1
Detailed descriptions for explanation of the figure are necessary in the text.
1) Although principle for intervention was not described in 2005 recommendation, the term ÓinterventionÓ is used in the figure 1 for emergency situations and controllable existing situation. We consider that description of principle for intervention should be restored in 2005 recommendation. For better understanding, actual change in dose should be shown with different color from that for levels.
2) Reduction by means of the optimization is quite different from site by site. Upper figure suggests that authorized level would be an optimized result. This means that further consideration for optimization seems not to be necessary.
3) We consider further effort for optimization should be required even under situation of the lower dose level than that authorized level.
4) In the middle figure, the term of intervention level is used. The intervention level was defined as avertable dose in previous publications such as Publication 82. The level was not directly related with process of optimization in previous publications. Optimization should be performed when there is a room for optimization even in the case under intervention level. In the lower figure, dose constraint is used in stead of action level in spite of some different usage in relation with optimization. Action level has been widely used for control of existing situation such as radon exposure. Usage of dose constraint for planned situation (practice) is considered to be different from that for existing situation. Action level for existing situation should be restored to avoid unnecessary confusion.
P50, in Introduction
1) It should be stated clearly that radon decay products contribute far larger than radon gas.
2) Thoron and its decay products should also be considered to protect.
3) Annual dose of 10 mSv/y should be fixed first, and then should be converted to the range of radon gas concentration in air, i.e., 600 Bq m-3. If dose conversion procedure would be revised, then the converted concentration should be shifted proportionally.
4) In the draft, 600 Bq m-3 is equivalent to the maximum constraint dose level (order of 10 mSv/y), and 200 Bq m-3 is regarded as the available level, that is easy to control. While, this should also be consistent with the system of action level of 600 Bq m-3 for existing house, and 200 Bq m-3 for new build house.
5) Equilibrium factor of 0.4 should be considered to be controllable by reducing aerosol (dust) concentration in air. Action levels mentioned above should be reevaluated in the equilibrium equivalent concentration (EEC)@rather than gas concentration.
P51, ajIdentification of radon-prone areas ....
ETo identify the radon-prone areas, not only the geological survey of uranium and thorium in the terrestrial materials but also the local characteristics of the houses and workplaces that would potentially cause the high radon concentration, i.e., airtight house, interior materials with high radium and thorium, etc.
P52, bjMeasurements of concentration levels
EPotential health impacts of thoron and its decay products should be emphasized as well as radon and its progeny. Measurements of decay products of both radon and thoron should be identified clearly in the text as main contributors of dose.
P52, cjImplementation of protection actions
EFundamentally, increased air exchange is an easy and essential option to reduce radon and thoron gases in the indoor air, but it should be noticed that active air exchanges by extractor fan might decompress the indoor air that may increase the intrusion of radon and thoron gases from the floor. Introduction of the air purifier would reduce the dose from the decay products, although it would not reduce the concentrations of radon and thoron gases.