Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
2 CONTROL OF OCCUPATIONAL EXPOSURES TO
RADIONUCLIDES
2.1 Limits, Constraints, Reference Levels and Investigation Levels
(52) For occupational exposure to ionising radiation, the Commission continues to
recommend that the primary annual limit relating to stochastic effects should be
expressed as an effective dose of 20 mSv, averaged over defined 5 year periods (100
mSv in 5 years), with the further provision that the annual effective dose should not
exceed 50 mSv in any single year (ICRP, 2007). To prevent deterministic effects,
there are additional annual limits on equivalent dose to the lens of the eye (20 mSv
averaged over defined 5 year periods, with no single year exceeding 50 mSv), the skin
(500 mSv), and the hands and feet (500 mSv), but these are generally not likely to be
relevant in the context of intakes of radionuclides. Where workers may be exposed to
both external radiation and intakes of radionuclides, the annual dose limit applies to
the sum of the effective doses from external radiations and the committed effective
dose from intakes of radionuclides occurring within the year.
(53) In the 2007 Recommendations (ICRP, 2007), emphasis was placed on the use
of dose constraints and reference levels. Dose constraints were included in the system
of radiological protection given in Publication 60 (ICRP, 1991) and their use is
developed further in the 2007 Recommendations. A dose constraint is a prospective
and source related restriction on the individual dose from a source in planned
exposure conditions (except in planned exposure of patients), which serves as an
upper bound on the predicted dose in the optimisation of protection for that source. It
is a level of dose above which it is unlikely that protection is optimised for a given
source of exposure, and for which, therefore, action must almost always be taken.
Dose constraints for planned situations represent a basic level of protection and will
always be lower than the pertinent dose limit. During planning it must be ensured that
the source concerned does not imply doses exceeding the dose constraint.
Optimisation of protection will establish an acceptable level of dose below the
constraint. This optimised level then becomes the expected outcome of the planned
protective actions (ICRP, 2007). The Commission has emphasised that dose
constraints are not to be used or understood as prescriptive regulatory limits.
(54) In an emergency or existing controllable exposure situation, the reference
levels are taken to represent the level of dose or risk above which it is judged to be
inappropriate to plan to allow exposures to occur, and for which therefore protective
actions should be planned and their extent be decided through optimisation. The
chosen value for a reference level will depend upon the prevailing circumstances of
the exposure situation under consideration (ICRP, 2007).
(55) The Commission’s constraints and reference levels apply across occupational,
public and medical exposures (ICRP, 2007) and three defined bands are
recommended. These are: ≤1 mSv; >1 - 20 mSv and >20-100 mSv. Doses greater
than 100 mSv are only considered in the context of life-saving actions. The first band,
≤1 mSv, applies to exposure situations where individuals receive exposures – usually
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