A vision of the future of radiological protection3 November 2002
The Nuclear Energy Agency (NEA) of the OECD has produced an expert group report entitled The Way Forward in Radiological Protection, to provide a new, broadly understood and accepted system of radiological protection.
In April 2000, the NEA Committee on Radiation Protection and Public Health (CRPPH) discussed the evolution of the system of radiation protection, and the concept of controllable dose.
A CRPPH working party on Controllable Dose and the Use of Collective Dose prepared a report. In addition, the Committee agreed that a new Expert Group on the Evolution of the System of Radiation Protection (EGRP) should be formed to continue these discussions.
The CRPPH gave the EGRP the following terms of reference:
• To identify the areas of the current system of radiological protection most in need of development. The Group should provide a prioritised list of areas that need work.
• To develop more detailed discussions of the top four priority issues, and prepare a report for the CRPPH with suggestions as to what changes should be made.
• To engage with others in discussions and activities.
• To use case studies to test the proposed changes, to ensure they move the system of radiological protection towards a more understandable, easy-to-apply and acceptable system.
• To report its recommendations to CRPPH for review and approval.
Motivation for change
Since the start of the 20th century, when the harmful effects of radiation were first observed, the aim of radiological protection has been to provide
adequate protection to people while not limiting the potential benefits that arise from activities that result in ionising radiation. Over the last few decades, there have been many studies on the effects of ionising radiation, ranging from studies into the effects on individual cells to studies looking at the effects of ionising radiation on large populations. The International Commission on Radiological Protection (ICRP) system of radiological protection that has evolved over the years covers many diverse radiological issues. It is not surprising that there are some perceived inconsistencies, which may lead to some issues not being adequately addressed.
For example, decommissioning of nuclear facilities requires considerable expenditure. The public want sufficient resources to minimise residual contamination. Governments, on the other hand, are keen to ensure that residual contamination is low, but not to the extent that scarce resources are used up reducing radiological risks which are already very low, at the expense of ignoring other ionising radiation hazards. Governments are increasingly concerned with finding an appropriate balance with allocation of resources to protect the public, and with a coherent approach to the management of all health risks.
The public wants to participate in decision making on issues that affect public health or the environment. This shows itself in an impetus for a clear distinction between roles and responsibilities. The current system of radiological protection does not sufficiently identify these boundaries.
Some employers are concerned that dose reduction efforts for occupational exposure are becoming unreasonable.
Another area of concern is the relationship between dose and risk. Although the effects of exposure to high levels of radiation can be predicted, there is no firm scientific evidence on potential health effects caused by very low doses. In view of this uncertainty, the ICRP has adopted the linear no-threshold (LNT) hypothesis to develop recommendations. This assumes that all exposure to radiation carries some risk, and that the risk is proportional to the exposure.
An area related to discussion of LNT is Effective Dose (E), the indicator used to predict the risk of cancer caused by radiation. E is calculated using the absorbed dose, and weighted by parameters representing susceptibility of exposed tissue and the effectiveness of the type of radiation causing the dose.
The CRPPH identified four areas where clarity and coherence could be improved to facilitate the task of regulators and implementers of radiological protection. These areas are:
• Numerical guidance: dose limits and intervention levels.
• The concepts of regulatory control, exemption and triviality.
• Justification and optimisation.
• Decision making versus decision aiding.
Numerical guidance: dose limits and intervention levels
Dose limits, dose constraints, intervention levels, and other numerical radiological protection criteria are all cases where international consensus on harmonisation of standards is required.
The boundary between unacceptable and tolerable is not a scientific question, and some have questioned the role of the ICRP in areas dominated by social judgement aspects. However, ICRP has, for many years, provided numerical recommendations on dose limits that have been widely implemented in national regulations and international standards.
Source-related dose constraints can be effective tools for public protection. This suggests that national regulatory authorities must consider the effects of multiple sources when fixing source-related dose constraints.
ICRP selected numerical dose limits for workers using comparison to "other occupations having high standards of safety." In selecting a numerical dose limit for the public, ICRP compared radiation to other socially accepted risks, stating: "It is reasonable to consider the magnitude of radiation risks in the general public in the light of public acceptance of other risks of everyday life." This ties selected dose limits to acceptance of other risks, implying that as social acceptance of risks change, dose limits must also change. This presents regulators with the need to periodically re-assess dose limits.
However, ICRP's description of the rationale for selection of the numerical values of worker and public dose limits leans more towards scientific issues than social judgements and international consensus. The system of radiological protection should explicitly recognise the fundamental differences between scientific facts, assumptions and social judgement. While the scientific rationale is necessary as input to discussions, and should be kept in future ICRP recommendations, the justification of numerical recommendations for dose limits should be expressed in terms of international consensus and social judgement.
To assist in international discussions of dose limits and intervention levels, there are several conclusions that can be drawn:
• There is a consensus that regulators need "numbers" as benchmarks for regulation. These can be limits, action levels, or reference levels.
• Points of reference are useful to justify numerical values.
• Experience and approaches from other industries could be studied.
The EGRP feels that the system of radiological protection should:
• Include dose limits which are socially well accepted and source-related dose constraints which are widely viewed as useful tools for regulators.
• Recognise the importance of social judgement aspects of setting numerical criteria, such as dose limits, for radiological protection purposes.
• Tie the rationale for numerical radiological protection criteria to international agreement, social judgement and a broader public acceptance of other risks.
• Propose guidance for addressing exposure situations that is flexible.
• Explain the relationship between the use of numerical radiological protection criteria for ongoing activities, and the flexible approach taken for actual situations.
Control, exemption and triviality
Triviality has received a lot of attention. The social judgement aspect inherent in the concept of triviality has taken on far more importance to the public than the scientific risk assessments stressed in existing guidance.
Initially, triviality was intended to designate exposures that were so low as to not require regulatory actions. However, the concept of triviality has not been accepted by the public. For example, release of slightly contaminated materials from decommissioning activities has been analysed using an approach similar to that used for exemption of smoke detectors from regulatory requirements. The fact that resulting doses have been below the pre-defined internationally-accepted level of triviality (10µSv/year individual dose, 1manSv/year collective dose) has not led in many instances to this practice being publicly accepted.
Generic use of a pre-defined, internationally-accepted level defining trivial dose is not universally accepted for all cases in modern society. As a result, triviality needs to be seen as part of the broader question of authorised release. If viewed this way, the concept of triviality is no longer required.
The need to modernise the current system of radiological protection arises from its relative variance between regulatory control of radioactivity based on the source of the radioactivity. These have been called exemption (in the case of materials that are not regulated), clearance (in the case of release of materials), authorised release (in the case of sites), authorised effluent release (in the case of gaseous and liquid effluents), and intervention exemption levels (in the case of commodities). These can be considered equal from the point of view of health effects, as a dose is identical, regardless of source.
Given the difference in social acceptance, the release of radioactive materials should be more subject to an authorisation optimisation process than a pre-defined triviality level below which no further actions are necessary. Some sources could be authorised on clearly explained grounds, for example, that they are not possible to control. Using this approach, other systems currently used could be eliminated.
For example, triviality is more socially divisive than it is useful.
Given that social judgements are key to reaching acceptable solutions, the following should be taken into account during authorisation:
• It should be clearly stated that the "free release" of radioactive materials implies governmental consent for any further use of materials. These releases will be irreversible, although releases can always be halted or discontinued should new elements bring the original authorisation study into question.
• To judge the acceptability of residual exposures resulting from release of materials, the absolute value of dose must be considered, as well as how easy it is to lower this dose.
• Those that are "worried" should be involved in the decision-making process.
• Discussions with interested parties during justification, authorisation and optimisation processes should include consideration of benefits as well as risks.
A framework for radiological protection
One area where a flexible, locally-focused "process approach" will not work is international trade. There is a need for an internationally agreed upon level below which international trade of commodities is not subject to radiological protection regulation.
The EGRP feels that the system of radiological protection should:
• Define an overarching approach considering all exposures and sources.
• Include use of a process of optimisation for authorisation of the release of sources from some or all regulatory control, and exposures to occur without the need to comply with some or all regulatory controls.
• Include an umbrella concept of authorisation to simplify the system of radiological protection.
• Provide guidance for the optimisation process used for the authorisation of release.
• Specify the types of dose constraints, if any, and identify internationally agreed upon numerical values for these dose contraints.
• Provide guidance for the development of locally applicable numerical values for dose constraints.
• Include internationally agreed upon radiological criteria below which the international trade of commodities would be free of radiological protection restrictions.