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INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION ——————————————————————————————————
Optimisation of Radiological
Protection in ICRP’s New
Recommendations
Stockholm, 7 December 2006
Lars-Erik Holm
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The System of Radiological Protection
• Types of exposure situations
• Types of exposure
• Identification of the exposed individuals
• Source-related and individual-related assessments
• The three fundamental principles of protection
• Levels of individual dose that require protective action
• Safety of radiation sources
• Implementation
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Linear-no-threshold (LNT) Model
… is the basis for:
• Averaging and summing of doses
• The concept of effective dose
• The concept of collective dose
• Individual dosimetry
• Keeping dose records
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• The nominal risk estimates are slightly smaller than in 1990, but in the same order of magnitude.
• The overall risk of 0.05 Sv-1 (0.00005 mSv -1) continues to be appropriate for purposes of radiological protection.
Summary of Radiation Risks
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Principles of Protection
Justification – Source related
Optimization - Source related
Dose limitation – Individual related
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Principles of Protection
Justification – Source related
Optimization - Source related
Dose limitation – Individual related
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The Principle of Optimisation of Protection
• In relation to any particular source,
- the magnitude of individual doses,
- the number of people exposed, and
- the likelihood of incurring exposures where these
are not certain to be received
should all be kept as low as reasonably achievable,
taking into account economic and societal factors.
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The Evolution of ALARA
1954: reduce exposures to the lowest possible level
1959: keep exposures as low as practicable
1966: keep exposures as low as readily achievable economic and social
considerations being taken into account
1973: keep exposures as low as reasonably achievable economic and
social considerations being taken into account
1977: keep exposures as low as reasonably achievable economic and
social factors being taken into account
2007: keep exposures as low as reasonably achievable economic and
societal factors being taken into account
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From Practices to Planned Situations
ICRP is moving away from
• a process-based protection approach to
• a situation-based approach
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Practices and Interventions
No procedural difference because in both cases,
• There is a maximum level of dose above which the regulator will demand action
• Optimisation of protection will reduce the level of dose at which action is taken
• No action to further reduce doses below the optimised level of protection
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Types of Exposure Situations
• Planned exposure: situations involving the planned introduction and operation of sources, incl. medical exposure of patients, decommissioning and waste disposal
• Emergency exposure: unexpected situations that occur during the operation of a planned situation, or from a malicious act, requiring urgent action
• Existing exposure: situations that already exist when a decision on control has to be taken, incl. natural background radiation and residues from past practices
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Reference Levels and Dose Constraints
= Values above which one plans not to go, and below which one strives to reduce all actual doses
Planned exposure: Dose constraint Diagnostic reference level
Emergency exposure: Reference level
Existing exposure: Reference level
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Reference Levels and Dose Constraints
• Apply to all situations
- The value will depend on the circumstances
• An integral part of prospectively optimising protection at the source
• If a relevant constraint or reference level was not complied with
- Further protection options must be considered
- Not necessarily a failure of protection
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The Use of Dose ConstraintsPLANNED EXPOSURE SITUATIONS
• For planned situations: a basic level of protection, less than limits
• Set for each source to ensure that the dose limits are not exceeded
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• For occupational exposure: typically set by operators or, for small companies, by regulatory authorities
• For public exposure: typically set by regulatory authorities
• For patients’ comforters and carers: typically set by the medical profession
Establishing Dose ConstraintsPLANNED EXPOSURE SITUATIONS
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The Use of Reference LevelsEMERGENCY AND EXISTING EXPOSURE SITUATIONS
• Prospectively as a level of ambition
• Retrospectively for assessing the effectiveness of protection
• Not as a mandatory level that must be achieved
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Projected Dose (mSv)
Characteristics and Requirements
20 - 100 Exceptional situations. Benefit on a case-by-case basis. Information, training and individual monitoring of workers, assessment of public doses.
1 - 20 Individual or societal benefit. Information, education and training. Individual monitoring or assessment.
0.01 - 1 Societal benefit (not individual). No information, training or individual monitoring. Assessment of doses for compliance.
Dose Constraints and Reference Levels
Type of Exposure Situation
Emergency
Existing
Planned
Planned
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• Large distributions of individual exposures
• Often affecting places of living
• Sometime difficult to control (most often mainly controllable through pathways)
• Time is a key parameter (step by step approach)
• In many cases, the level of exposure is driven by individual behaviour
Characteristics of Existing Situations
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Individual dose level
Reference levelNo. of individuals
Step 1 Step 2 Step 3
Evolution of the Individual Dose Distribution with Time
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Publications 60 and 63
INTERVENTION and no action below ACTION LEVELS
Recommend values for the AVERTED dose for SINGLE countermeasures where intervention is almost always justified:
• Sheltering
• Administration of stable iodine
• Evacuation
• Relocation
• Restriction to a single foodstuff
ICRP 2007
OPTIMISATION below REFERENCE LEVELS
Recommends an upper value of the PROJECTED dose (= reference level) received via ALL pathways below which optimisation is applied.
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Prospective
PreparednessRetrospective
Response
Reference levelOption A
Option B
Option C
Select Option B Dose distributionfor which planned protection strategyhas been implemented
Optimise
Focus particular attention on this part of the dose distribution
Dose distributionafter further optimisedprotection strategies, ifany, have been applied
Application of Reference Levels
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1. Consider each option of a protection measure on its
own merits.
2. Consider simultaneously doses that would be incurred
via all exposure pathways, some subject to protective
actions and some not.
3. If the total residual dose to some individuals is
unacceptably high, the feasibility of additional protective
measures should be considered.
Optimisation Below Reference Levels
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Time
Reference level
mSv/yr
Early Intermediate Late Phase
100
10
1
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Conclusion – Reference Levels
• Basically, the same approach as for constraints in planned situations:– Characterizing the exposure situation– Setting a level of ambition (reference level) – Optimizing protection taking into account the
prevailing circumstances
• Iterative process for implementing optimisation
• General improvement of the quality of protection for existing and emergency situations
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The System of Radiological Protection in the 2007 Recommendations
• Emphasizes a strong radiation safety culture through iterative review and assessment to optimise radiation doses
• Optimisation involves evaluating and incorporating measures that tend to lower doses to workers, the public or patients
• Optimisation also entails consideration of avoidance of accidents and other potential exposures
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Optimisation of Protection
• The optimisation is a forward looking iterative process aimed at preventing exposures before they occur.
• Optimisation is the responsibility of the operating management, subject to the requirements of the authority.
• An active safety culture supports the successful application of optimisation by both the operational management and by the authority.
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Optimisation of Protection
• All aspects of optimisation cannot be codified; optimisation is more an obligation of means than of results.
• The authority should focus on processes, procedures and judgements rather than specific outcomes.
• An open dialogue must be established between the authority and the operating management to ensure a successful optimisation process.
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Practical Implications
OPERATIONAL MANAGEMENT
• Develop and provide internal policies, priorities, rules and procedures, to
• Ensure the existence of a safety culture at all levels of management and the workforce
COMPETENT AUTHORITIES
• Establish clear policies and processes for decision-making regarding the authorisation of proposed activities
• Regulatory requirements should include the need for an active safety culture in both authority and operating management.
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TG OPIMISATION of PROTECTION
The Optimisation Process
Optimisation is a forward-looking iterative process aimed at preventing exposures before they occur.
Evaluation of exposure situations to identify the
need for action
Identification of protection options
Selection of the best option under the prevailing
circumstances
Implementation of the protection option
Measurement of
performances
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For decision-aiding, more information is often necessary, e.g. for the workforce:
• Number exposed, mean dose, dose range, task-related dose, etc.
• When, where, how and by whom are exposures received?
For decision-making, it may be reasonable to give more weight to doses that are
• Moderate or high• Received in the near future
The Collective Dose
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THE DOSE MATRI X THE DOSE MATRI X –– (i)(i)
DOSE Weighting factorDOSE Weighting factor
TIME yrsTIME yrs
101 102 103 104 105 106 107
11
0.10.1
0.010.01
0.0010.001
0.00010.0001
Based on the uncertainty Based on the uncertainty of dose calculationof dose calculation
THE DOSE MATRIX THE DOSE MATRIX –– (ii)(ii)
DOSE Weighting factorDOSE Weighting factor
DOSE mSvDOSE mSv
100 10-1 10-2 10-3 10-4 10-5 10-6
11
0.10.1
0.010.01
0.0010.001
0.00010.0001
Based on the uncertainty Based on the uncertainty of dose calculationof dose calculation
Examples of Dose Weighting
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TG OPIMISATION of PROTECTION
Selecting Protection Options
QUANTITATIVE TOOLS
Methodology and tools were developed in the 1980s to compare protection options with multi-attributes and characteristics taking into account ethical, social and economical considerations.They are still valid.
ICRP warns against an application of these techniques alone.
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Optimisation and BAT
• For the control of radioactive emissions to the
environment the principle of the best available technology,
not entailing excessive costs (BAT), may be used.
• The principles of optimisation and BAT complement each
other.
• The control of exposures in relation to health will be driven
by the optimisation of estimated radiation doses.
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Optimisation and BAT
• Optimisation assumes an object of protection and a defined detriment of radiation exposure.
• An optimisation cannot be carried out as simply when the benefit and detriment cannot be quantified, e.g. in connection with a future release– the probability is difficult to define– the consequences for the environment cannot be quantified using the
collective dose.
• BAT can be used to achieve a high level of protection without quantification of these parameters in greater detail.
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Optimisation and BATTHE CASE OF SPENT FUEL REPOSITORY
• The difficulty of predicting the future development of society makes optimisation difficult– We do not know what the biosphere will look like
• A minor release is better than a major release, even if the society which is affected is unknown. Therefore, the barrier system must be as robust as possible.
• Repository barriers fulfilling reasonable safety requirements can be said to meet the BAT requirement.
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Optimisation and BAT
Protection of human
health
BAT optimisation BAT good protective
capabilities and robustness
Protection of the
environment
BAT good protective
capabilities and robustness
BAT good protective
capabilities and robustness
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Practical Application of Optimisation and BAT
• Optimisation is a tool to minimise risk using risk (or dose) calculations
• BAT aims to hinder, limit and delay releases as far as reasonably possible
• Optimisation and BAT are important regulatory (societal) tools for ensuring an attitude of doing as good as reasonably possible
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Time Schedule
• December 2006: Main Commission working on final draft of
the new recommendations
• January 2007: The draft will be put on ICRP’s website as
a progress report.
• March 2007: Adoption of the new recommendations