Transcript Ingen bildrubrik

5th ISOE European Workshop on
Occupational Exposure Management at Nuclear Facilities
The New ICRP Recommendations
Essen, 15 March 2006
Lars-Erik Holm
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ICRP’s 2006 Recommendations
Volume 36, Issue 4, 2006
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Aims and scope
Biological aspects
Dosimetric quantities
The system of radiological protection
Medical exposures
Recommendations of the
International Commission on
Natural exposures
Radiological Protection, 2006
Potential exposures
Emergency situations
The scope of regulating radiological protection
Protection of the environment
Implementation of the Commission’s recommendations
The radiological protection paradigm
Glossary
References
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More Continuity than Change in
the 2006 Recommendations
• Most recommendations will remain - because they work
and are clear
… and some things are to
• Be explained - because more guidance is needed
• Be added - because there has been a void
• Differ - because understanding has evolved
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Major Features I
• Maintaining the 3 principles of radiological protection, and clarifying
how they apply to sources and the individual;
• Updating the radiation and tissue weighting factors;
• Maintaining the dose limits that represent the most that will be
accepted in planned situations by regulatory authorities;
• Using the concept of constraints in the source-related protection to
all situations. The constraints quantify the most fundamental levels of
protection for workers and the public from single sources;
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Major Features II
• Replacing ’practices’ and ’interventions’ with 3 types of
exposure situations which address all conceivable
circumstances:
- planned situations;
- emergency situations; and
- existing exposure situations.
• Including a policy for protection of the environment.
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The Aim of the Recommendations
• To provide an appropriate standard of protection for
people and the environment, without unduly limiting the
beneficial actions giving rise to radiation exposure.
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• The new recommendations consolidate and add to
previous recommendations issued in various ICRP
publications.
• The existing numerical recommendations in the policy
guidance given since 1991 remain valid unless otherwise
stated.
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Building Blocks
C1: Low-Dose Extrapolation of Radiation-Related Cancer Risk
C1: Biological and Epidemiological Information on Health Risks
Attributable to Ionising Radiation
C2: Dosimetric Quantities Used in Radiological Protection
C3: Radiological Protection in Medicine
C4: Optimisation of Protection
C4: Assessing Dose to the Representative Individual
MC: The Scope of Radiological Protection Regulations
MC: The Radiological Protection Paradigm
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Radiation Weighting Factors, wR
Type and energy
range
Publication 60
2006
Photons, all energies
1
1
Electrons and muons,
all energies
1
1
Protons
5
2
Alpha particles
20
20
Stepwise
function
Continuous
function
Neutrons
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New Reference Phantoms
MIRD Phantom
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Voxel Male and Female Phantoms
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Main Conclusions on Biology
• Dose-response for cancer and hereditary effects: A simple
proportionate relationship at low doses between dose and risk.
• DDREF: Retain a value of 2.
• Nominal probability coefficients for cancer: 5.5 10-2 Sv-1 for
whole population and 4.1 10-2 Sv-1 for adult workers.
• Nominal probability coefficients for heritable diseases: Up to
2nd generation: 0.2 10-2 Sv-1 for whole population and 0.1 10-2 Sv-1
for adult workers.
• Risks of non-cancer diseases: Great uncertainty on dose
response < 1 Sv; no judgement on low dose risk possible.
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Tissue Weighting Factors, wT
Tissue
1
wT
∑ wT
Bone-marrow, breast, colon, lung, stomach,
remainder tissues1
0.12
0.72
Gonads
0.08
0.08
Bladder, oesophagus, liver, thyroid
0.04
0.16
Bone surface, brain, salivary glands, skin
0.01
0.04
Nominal wT divided equally between 14 tissues.
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NOMINAL RISK COEFFICIENTS FOR
STOCHASTIC EFFECTS (% Sv-1)
Exposed
population
Cancer
Heritable effects
Total
ICRP60
2006
ICRP60
2006
ICRP60
2006
Whole
6.0
5.5
1.3
0.2
7.3
5.7
Adult
4.8
4.1
0.8
0.1
5.6
4.2
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Principles of Protection
FOR SINGLE SOURCES
JUSTIFICATION
Any decision that alters the existing radiation
exposure situation, e.g., by introducing a new
radiation source or by reducing existing exposure,
should do more good than harm.
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Principles of Protection
FOR SINGLE SOURCES
OPTIMISATION
Optimisation of protection should ensure the selection of the
best protection option under the prevailing circumstances, and
maximising the margin of good over harm. This procedure
should be constrained by restrictions on the doses or risks to
individuals (dose or risk constraints).
Optimisation involves keeping exposures as low as reasonably
achievable, taking into account economic and social factors, as
well as any inequity in the distribution of doses and benefits
amongst those exposed.
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Principles of Protection
FOR INDIVIDUALS
DOSE LIMITS
In planned situations, the total dose to any individual from all
the regulated sources should not exceed the appropriate dose
limits specified by the Commission.
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Restrictions and Reference Levels
in Publication 60
Restrictions
• Dose limit
• Dose constraint
Reference levels
• Recording level
• Investigation level
• Intervention level
• Action level
• Diagnostic reference level
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Dose Constraint 2006 (I)
• It is the most fundamental level of protection for the most
exposed individuals from a single source within a class of
exposure.
• It applies to all situations;
• It is used prospectively as the starting point of the
optimisation process;
• It is not a form of retrospective dose limitation.
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Dose Constraint 2006 (II)
• In planned situations, it is less than limits;
• In emergency or existing exposure situations, it represents
the level of dose/risk where action is almost always
warranted;
• The chosen value will depend upon the circumstances of
the exposure;
• It will be established at the national or local level by
regulators or operators.
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Dose Constraint 2006 (III)
• The numerical criteria recommended by the Commission in
Publication 60 and thereafter can all be regarded as
constraints.
• The values fall into three defined bands: 0.01-1 mSv, 1-20 mSv
and 20-100 mSv.
• These bands will enable selection of an appropriate value for a
constraint for a specific situation that has not been addressed
explicitly by the Commission.
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ICRP’s Band of Constraints from
Single Dominant Sources
BANDS OF PROJECTED
DOSE
20 - 100 mSv
1 - 20 mSv
0.01 - 1 mSv
REQUIREMENTS
Benefit on a case-by-case basis. Information,
training and individual monitoring of workers,
assessment of public doses.
Individual direct or indirect benefit.
Information, training and either individual
monitoring or assessment.
Societal benefit (not individual).
No information, training or individual
monitoring. Assessment of doses for
compliance.
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Additional Radiation Dose and Risk
THE CASE FOR PLANNED SITUATIONS
UNACCEPTABLE RISK
DOSE LIMIT
TOLERABLE RISK
DOSE CONSTRAINT
ACCEPTABLE RISK
OPTIMISATION
TRIVIAL RISK
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Constraints for Radon
ICRP’s policy is based upon setting a level of effective dose
from radon where action would be warranted:
10 mSv per year
ICRP’s constraints are set where action is almost always
warranted:
Home 500 Bq m-3
Work 1250 Bq m-3
National regulators apply the optimisation of protection to arrive
at the level at which to act.
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Diagnostic Reference Level
• The diagnostic reference level has as its objective the
optimization of protection.
• The dose to the patient from a specified diagnostic
procedure should not normally exceed the diagnostic
reference level for that procedure.
• It does not relate to individual patients.
• Conceptually, the diagnostic reference level serves as
a kind of constraint for a specified examination/
procedure.
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Exclusion from Legislation
ICRP TG recommends to exclude radiation exposure
situations that cannot reasonably be considered
amenable as to control:
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Cosmic radiation at ground level;
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Radionuclides of natural origin in the human body;
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Radon in ambient air: < 100 (or 40) Bq/m3; and
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Any other exposure situation that the legislator judge to
be unamenable to control.
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Exclusion or Exemption
ICRP TG recommends levels for exclusion or generic exemption
for:
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Artificial radionuclides:
< 1 Bq/kg for alpha emitters
< 10 Bq/kg for beta/gamma emitters;
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Natural radionuclides in materials, except building materials:
< 1000 Bq/kg for the head of the 238U and 232Th;
< 10 000 Bq/kg for 40K
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Building materials: may warrant a more restrictive
consideration of the sum of 238U, 232Th and 40K, and the
radiological implications should be carefully analyzed.
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Exemption
An important component of regulatory functions.
The principles for exempting a practice or a source within a
practice:
• individual risks must be sufficiently low as not to warrant
regulatory concern (0.01 mSv a-1);
• radiological protection, including the efforts of regulatory
control, must be optimised; and
• the practice must be justified and its sources should be
inherently safe.
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Recommended Exemption
• Devices emitting adventitious radiation of max. 5 keV and
max. 1 Sv h-1 at 0.1 m from any surface of the device;
• Radionuclides in activity concentrations smaller than those
specified by FAO and WHO for foodstuff and drinking
water, and by the IAEA for non-edible commodities, for
radiation sources and for materials in transport.
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Time Schedule
• March 2006: Main Commission to discuss new draft
recommendations
• may 2006: New international consultation of draft
recommendations
• November 2006: Main Commission to discuss revised draft
recommendations
• December 2006: Earliest possible date of ICRP adoption
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