|Canadian Nuclear Safety Commission (CNSC) Staff Comments on the 2006 Draft Recommendations of the International Commission on Radiological Protection
Some of these comments are shared with those from the Canadian workshop held on August 10, 2006. These comments, already submitted separately as part of the comments from that workshop, are indicated by an “*”.
The new draft of the recommendations is an improvement over the previous draft and the CNSC is encouraged that many of the comments made on the earlier draft have been in incorporated.
CNSC GC 1. Constraints
Because the treatment of constraints in the current draft is spread throughout the document, unclear, and in many places inconsistent (examples follow), it is very difficult to review and understand in a comprehensive way even after several close readings. Therefore, we strongly recommend that the treatment of constraints be reorganized to put all central ideas, and most descriptive text, into a single section, and that inconsistencies be resolved.
A consequence of the current treatment is that we cannot provide comprehensive comments on constraints. The text in this section is our best effort to provide some guidance with respect to how the treatment of constraints could be improved so that the ICRP would be able to receive more comprehensive comments following release of the next draft.
The ICRP continues to promote the concept of constraints as the “the fundamental level of protection”. However, still lacking are:
- a clear explanation of what gap they fill in the system of protection currently employed;
- a clear rationale demonstrating that raising the profile of this tool is justified by a commensurate increase in safety; and,
- a clear explanation of how the ICRP would see them work in practice.
To be specific, we strongly recommend that constraints not be described as the “fundamental level of protection”, but rather, if retained at all for “planned” exposure situations, described as a possible tool in the optimization process. Further, we recommend that the ICRP describe the gap that constrains fill in the current system, provide a clear rationale for their use, and describe more fully how they would be used in practice.
Current international radiation protection regulatory frameworks for planned exposure situations (the most common case) are based upon dose limits as the upper bounds of exposure and application of ALARA programs to further reduce that dose. The addition of constraints (as we interpret them) to this system is not a trivial effort; indeed, it would impact on a very wide range of regulatory activities requiring, for example:
• the identification of all “sources” at all licenced facilities,
• a review of all exposures due to those “sources”,
• determination of an acceptable constraint for exposures from those sources,
• amending current regulation to include source specific constraints and the required response to a constraint exceedence, and,
• development of a program to assess compliance with the constraints.
In addition, many regulatory bodies must now demonstrate a clear need for regulations indicating the benefit and cost of that regulation. The draft Recommendations themselves enforce this criterion in Paragraph (43) that states “provided that every individual is afforded an acceptable level of protection, regulatory control should not be applied if it is unfeasible or the societal effort needed for its applications would be disproportionate to the saving in detriment it would be considered to achieve.”
However, with respect to the draft Recommendations it is not evident that this criterion has been met. There is no argument provided of the need, justification or benefit for this additional regulatory control on exposures.
In addition, there is little indication given as to the intended response to an exceedence of a constraint. If the constraint is a “the fundamental level of protection”, it will need to be an important part of the regulatory framework, equivalent to that of a dose limit. An exceedence of a constraint would then be expected to have some significant consequence, but little in this regard has been provided in the draft Recommendations.
Examples, especially complex ones, would be helpful in the understanding. There should be a clear process provided to show how the constraint is derived and how it fits into the optimization process.
As a prospective tool only (197), dose constraints have little value over and above the requirement keep doses ALARA (i.e. to optimize protection). Indeed, the optimization process should result in doses below any reasonable dose constraint, and therefore if the optimization process is followed, dose constraints become redundant.
As a retrospective tool, constraints could be operationally useful as “a level above which action to reduce doses must almost always be taken” (224). That is, exceedance of a constraint during operations is a trigger to re-verify whether protection remains optimized and, if it is not, to take action to reduce doses. Canada has used a system like this successfully for several years, setting levels which, if exceeded, require a licensee to investigate, report, and take action to reduce dose if appropriate.
Numerous inconsistencies relating to the treatment of constraints were found throughout the document. Some examples follow:
Examples of inconsistencies
It is noted here that the definition of ALARA now includes constraints indicating that the constraint is in place before ALARA is applied. However, the second bullet in paragraph (196), which outlines the optimization process, includes “selection of an appropriate value for the constraint”, indicating that the constraint is part of the optimization process.
This paragraph generates more confusion: “…constraint of 100 mSv….should be considered to apply to the total dose to an individual from all sources.” This is could be interpreted as a dose limit.
Pertaining to a discussion of single source exposure and multiple source exposures, it is not clear what is meant by “additional restrictions are needed in the situation where one individual is exposed to several sources”. Is it implying that where a worker may be exposed to many different sources than that worker may exceed a dose limit? If so, this appears to be an artifact of the source constraint system, in that if a dose to the worker in general was controlled, this would not be an issue. By the term “restrictions”, does the ICRP mean additional “worker constraints” are required? Clarification is required.
If the constraint is set before the optimization process and is based upon past operating experience, when would an optimization process suggest a protection option that would increase doses above a constraint? This paragraph is nonsensical and should be removed.
If constraints should be viewed as “a level of ambition and not as a mandatory level…”, then they are targets. The radiation protection community already uses targets: administration and action levels. Furthermore, in most regulatory structures, the only way to set constraints at the “national or local level” is to incorporate them within the regulations in which case they will not be at a “level of ambition and not as a mandatory level”.
This paragraph states that constraints define a level above which action to reduce doses must always be taken, but it does not state what that action is and whether the action is on the part of the user, the regulator, or both. What those actions are should be elaborated and it should also be stated how this action differs from exceeding a dose limit.
Paragraph (225) and (226)
These two paragraphs appear to have some conflict where (225) suggests a risk-informed approach, but (226) states that it is not relevant to determine a priori a dose level below which the optimization process should stop. However, if dose is taken as an analogue for risk, there must be some dose (risk level) below which the expenditure of any effort would not be optimal.
This paragraph states that once optimization has resulted in activities well below the constraints, no further action is required. This is contrary to the application of optimization, where one should be continually looking for ways to reduce dose. It is also in conflict with Para (226) which stated that “it is not relevant to determine a priori a dose level below which the optimization process should stop.”
CNSC GC 2. Sources
With respect to “sources”, upon which it is recommended that a constraint be placed, examples are only given for simple situations such as exposure to a member of the public from a licenced activity. Stating “that the class of occupation should be specified in broad terms” is not helpful when “dose constraints (on sources) are to be fixed at the national or local level” (which implies regulation). No guidance is given for more complex situations such as nuclear power plant workers, where there are potentially multiple sources of radiation and radioisotopes.
With respect to the definition of a single source we would recommend expanding it as follows:
“Any physical entity or procedure that results in a potentially quantifiable radiation dose to a person or group of persons. It can be a physical source (e.g., a quantity of radioactive material or an x-ray machine), a facility (e.g., a hospital or nuclear power plant) or a class of operations or physical sources having similar characteristics (e.g., nuclear medicine procedures, background radiation).”
States that ‘when using a dose constraint, a designer should specify the sources to which it is linked to avoid confusion with other sources to which the workforce might be concurrently exposed”. This implies that one worker may encounter more than one constraint in his work. It is also not evident how these source constraints would differ from dose-budgeted work plans. The logistics of having a worker exposed to a number of “sources” is complex and further explanation and examples are required, especially with respect to dose assessment from a multitude of sources.
We recommend the ICRP explain why it believes that optimization can only be achieved by the use of “constraints”. Optimization of worker dose has been done for at least the last 30 years and while some means of optimization have included administrative limits (or constraints) and dose targets to drive the process, others have just looked at means of reducing dose by examining work practices and engineering design. Certainly dose constraints are not a necessity for optimization.
CNSC GC 3. Clearance
In order to better reflect the reality of the regulation of radioactive material, it is strongly recommended that the ICRP adopt the IAEA concept and definition of clearance to allow the unconditional release of materials from regulatory control.* At a minimum, the ICRP should very clearly explain how this widely used concept fits into their recommended system of protection.
Presently there is an inconsistency in the application of the concepts of clearance, exemption and exclusion in the regulation of nuclear materials, for example, IAEA TS-R-1 Regulations for the Safe Transport of Radioactive Material, 2005 Edition Safety has more restrictive activity limits than does that recommended by the IAEA in RS-G-1.7 Application of the Concepts of Exclusion, Exemption and Clearance Safety Guide and Requirements. While the ICRP cannot be responsible for the publications of the IAEA, it is suggested that the ICRP state that where exemption and clearance limits are used, the determination of those values should account for all reasonable and probable uses and that the final determined exemption or clearance activity would be applicable for all international standards (e.g., consistency between RSG 1.7 and TSR 1). *
1.2 The development of the Commission’s recommendations
CNSC SC 1. It is suggested that a paragraph be included that outlines how the risk varies with age and perhaps include a recommendation as to which ages radiation-related work should be restricted to, similar to that done for gender.
The Aims and Scope of the Recommendations
CNSC SC 2. The absence of recommendations regarding protection of the environment should be stated in the Scope. *
CNSC SC 3. It is recommended that a statement be given indicating that job rotation should not be seen as a means of dose optimization if it increases the collective dose.
In the second bullet, under the “The principle of optimization of protection”, the phrase “as well as any inequity in the distribution of doses and benefits amongst those exposed” is interpreted to mean that within a group, radiation work should be equitable. However, it could also be interpreted to mean that job rotation could be seen as a means of optimizing dose to the individual (at the expense of the collective dose). This does not appear to be the intent as paragraph (228) states “there is the additional expectation to reduce the number of exposed individuals.”
2.4 Exclusion and exemption
Paragraph (45) and (46)
CNSC SC 4. It is recommended that the full intended flexibility of the 10 µSv criterion (10’s µSv rather than “about 10 µSv”) be indicated in the main text.
This paragraph states that “practices and sources… … may be exempted from some requirements… (where)… … the attributable risk is around 10 µSv.” Conversely, in Section 41 of the ICRP draft The Scope of Radiological Protection Regulations (2006), the flexibility of the 10 µSv criterion is stated as “some 10s of microsieverts per year… …would be acceptable as trivial dose”. In a regulatory sense, the term “around 10 µSv” could be interpreted in a strict sense of plus or minus 5, whereas it is clear in the foundation document that the intended flexibility is much greater, in the range of 10-50 µSv. *
3. Biological Aspects of Radiological Protection
CNSC SC 5. In the first sentence, the word “criteria” implies levels. Clarification is required.
3.2.3 Detriment adjusted nominal risk coefficients for cancer and hereditary effects
Paragraph (68) and (72)
CNSC SC 6. It is recommended that the wording uses in paragraph (68) with respect to exposures over a couple of generations be the same as that in paragraph (72).
4. Dosimetric Quantities
4.3.3 Equivalent dose and radiation weighting factors
CNSC SC 7. We recommend that the ICRP propose a special name for units of equivalent dose other than the Sievert, so that it can more easily be distinguished from effective dose.
4.3.5 Gender Averaging
CNSC SC 8. In order to calculate the “arithmetic mean of the equivalent doses” to the remainder organs, the summation formula must be divided by the number of tissues (13).
The equations are missing a factor of “1/13”, i.e. should be
HMRT = (1/13) HMT and HFRT = (1/13) HFT
4.5.2 Internal Radiation Exposure
CNSC SC 9. The text should indicate that adults are persons 18 years of age or older, and children are persons under 18 years of age.
Section 4.5.7 Collective dose
CNSC SC 10. For the formula in this paragraph, it needs to be corrected from “…where dN/dE denoted …” to “…where dN denoted…” so that it reflects the number of individuals who are exposed to an effective dose…
5. THE SYSTEM OF RADIOLOGICAL PROTECTION OF HUMANS
5.1. The definition of a single source
CNSC SC 11. It is suggested that examples and the boundaries be provided of “artificially subdividing a source” and “excessively aggregating sources” .
The definition of a “source” is relatively loose and no complex examples are given so it is difficult to know at what point one would be “artificially subdividing a source in order to avoid the need for protection action” and “excessively aggregating sources to exaggerate the need for action”
5.2 Types of exposure situations
CNSC SC 12. The ICRP should clarify whether “operated outside the Commission’s recommendations” refers to practices which are in contravention of past ICRP recommendations, or something else. In addition the ICRP should explain what is intended by “residues from past practices”.
The description of existing exposure situations is vague, i.e.” residues from past practices that were operated outside the Commission’s recommendations”. Does this also include orphaned sources, i.e. sources that have been improperly disposed of or abandoned?
5.3. Categories of exposure
CNSC SC 13. A reference is required in the references section for Publication 101 (ICRP, 2006b)
5.3.1. Occupational Exposure
CNSC SC 14. “…situations that can reasonably be regarded as being the responsibility of operating management.” requires clarification. Examples of these situations would be useful.
CNSC SC 15. The present definition of a radiation worker is vague and would include an administrative support person who distributes dosimeters to workers or one who tracks doses received by workers, but may never be occupationally exposed to radiation. The definition of radiation worker requires more criteria so as to exclude administrative staff.
5.4.3. Members of the public
CNSC SC 16. The premise behind the statement “…neither the operator nor the regulator has information about the totality of sources contributing to dose to be limited in planned situations” is not understood. Surely a responsible operator knows what their planned releases are and they can estimate the dose to a member of the public from these. True they are estimates, but all dose assessments are only estimates. In any event, it is not clear how this purported lack of information justifies constraints since, even with a constraint, one would have to be able to estimate the dose to the “representative individual” to assess compliance.
We recommend that the statement “…neither the operator nor the regulator has information about the totality of sources contributing to dose to be limited in planned situations” be either further elaborated or removed.
5.6. Levels of protection
CNSC SC 17. In the last sentence it states that protection from single sources is achieved by the use of constraints during the optimization process. While constraints could be used in optimizing doses from single sources, they are not the only means to do so. Dose or exposure levels that would indicate that doses are no longer optimized are more logically linked to ALARA than are constraints.
It is recommended that the last sentence of this paragraph be modified to indicate that the use of constraints is one way in which protection from single sources can be optimized.
See comment on paragraph (174) CNSC SC 16.
5.8 Optimization of protection
CNSC SC 18. The optimization process will differ greatly between that for occupational optimization and that for public and emergency situations. Recommendations currently do not specifically address this issue and they should for clarity. It is recommended that Section 5.8 should be restructured to reflect the specific exposure situation.*
CNSC SC 19. The 2nd bullet indicates that ALARA (optimization) requires the introduction of a “constraint”. We do not agree with this. The optimization process requires the use of parameters that demonstrate the effectiveness of the radiation protection program and these may or may not be constraints. It is recommended that the text in the second bullet indicate that constraints are one way in which protection can be optimized.
CNSC SC 20. ICRP-60 and the current draft (199) both link dose constraints to the limitation of inequity in dose distribution. However, limitation of maximum individual dose is the fundamental principle by which the system of protection seeks to ensure an adequate degree of equity in dose distribution to members of the society, regardless of overall benefit to society. It is our view that individual dose limits are adequate to ensure reasonable dose equity, and therefore constraints are redundant for this purpose. Trying to link constraints to two of the three fundamental principles (optimization of protection and limitation of maximum individual dose) also adds unnecessary confusion.
We recommend that links in (199) and elsewhere between constraints and dose equity be removed.
CNSC SC 21. This paragraph states that dose constraints are fixed at the national or local level, which in our interpretation includes all levels of regulatory control. Suggest replacing with “fixed at the appropriate regulatory level.”
CNSC SC 22. As mentioned in the paragraph, dose constraints can be established by the regulator but by necessity, this must be done through consultation with the regulatee.
With respect to the establishment of dose constraints, we would recommend that this be revised to allow greater input from the operator.
CNSC SC 23 It is not clear where a maximum constraint of 100 mSv in a year would apply. If this is a source related constraint and not a risk related one, it is not evident why it is above the dose limit. If there are extenuating circumstances, they should be provided. An example should be provided of when there may be a constraint in excess of the dose limit.
5.8.6 Dose constraints in medical exposure of patients
CNSC SC 24. In the second half of this paragraph, the Commission recommends that “where verification is not possible… … it would be prudent to apply a constraint of the order of 0.1 mSv per year to the prolonged component of the dose.” It is not evident how setting a dose constraint in this situation would be practical, since if verification is not possible, one cannot assess compliance. A better means of control would be to control the emissions from the facility.
It is suggested that the recommendation to use a constraint in the case of non-verifiable public doses be replaced with a recommendation that limirs be placed on measurable releases from the facility.
CNSC SC 25.
It is not apparent which specific “existing” exposure scenarios are relevant to this recommendation. In addition, of what value is 100 mSv or 20 mSv per year when the public dose limit is 1 mSv per year?
5.8.7 Application of optimization and constraints
CNSC SC 26. We recommended that the term “almost always” be replaced with “usually”.
CNSC SC 27. We recommend that (197) and elsewhere be revised to more consistently state or clarify the retrospective use of dose constraints (e.g. they are used in some circumstances as action levels (reference (279)).
CNSC SC 28. We suggest that a phrase be added in the brackets (economic, human, impact on other risks, social political, etc.) so that an optimized dose does not result in another elevated risk. (e.g., wearing respirators to reduce dose may increase risk of cardiac arrest.)
CNSC SC 29. The comment “there is the additional expectation to reduce the number of exposed individuals” is well taken. It is suggested that the statement go one step further and state that while optimization maybe used to limit inequalities in dose amongst a population, the use of job rotation should not be considered as a primary means to meet dose limit or constraints and cannot be considered optimization if the collective dose increases through the dose equalization process.
…Given the wealth of data on domestic exposure to radon, the Commission now recommends that the estimation of risk from domestic radon exposure be based on the results of pooled residential case control radon studies…
CNSC SC 30. Notwithstanding the recently available pooled studies, there is still great value in the miner epidemiology studies for investigating dose response relationships and confounding effects of smoking and exposure to other agents.*
Table 6: Constraints for Radon-222
CNSC SC 31 According to Paragraph (300), the title of this table should be ‘Action Levels for Radon-222’.
…In such exposure situations, the Commission recommends that the constraint for radon exposure in the workplace should be set in terms of dose at a value that ensures compliance with the Commission’s occupational dose limits…
CNSC SC 32. There is not universal agreement on the conversion of radon exposure to dose; however, the detriment from exposure to radon is well known from epidemiology. Therefore, it would be appropriate to use a summation formula with risk (detriment) equivalent denominators. *
…The problems posed by radon-220 (thoron) are much less widespread, and generally more tractable, than those posed by radon-222…
CNSC SC 33. This is debatable. Based on recent discussions at UNSCEAR and published literature, possible issues with radon-220 (thoron) are more widespread than previously thought. This paragraph should be reworded.*
This paragraph implies that dose constraint is a dose limit which may lead to confusion. Recommended that this paragraph be revised.*
9.1 Types of emergency situations
CNSC SC 34. It is not clear what “almost mandatory” means or implies. In the Canadian regulatory framework (which probably reflects that of most developed countries) you can either legally prescribe a requirement, which makes it mandatory, accept it when proposed in a licensee application (which would not apply in this instance), or provide it as a guideline. We recommend that a better term than “almost mandatory” be used, perhaps proposing it in a guide for emergency responders.
11.5 The classification of workplaces and working conditions
CNSC SC 35. A “controlled area” also has the attribute that access to the area is controlled by authorization or procedures.
CNSC SC 36. Collective Effective Dose, S: See comment on paragraph (148).
CNSC SC 37. Committed Effective Dose: See comment on paragraph (128).
CNSC SC 38. Controlled area: See comment on paragraph (394).
CNSC SC 39. RBE, Relative Biological Effectiveness (RBE): There are two entries in the glossary for the same term, the one for Relative Biological Effectiveness having more detail. We recommended that both entries either have the same information or the reader is directed from the short entry to the full one.
CNSC SC 40. Radiation Worker – Suggest addition of this term to glossary
CNSC SC 41. Sievert: “radiation-weighted dose” has not been defined.
CNSC SC 42. Track Structure: “…passage of a radiation track” should be “…passage of radiation”.