Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
including measurement uncertainties. Two types of analysis are discussed: reference
evaluation and site-specific evaluation.
6.2 Types of Analysis
6.2.1 Basic evaluation with ICRP default biokinetic and dosimetric
computational models
(309) For installations and tasks where the annual committed effective doses to
workers from intakes of radionuclides assessed prospectively are low (not likely to
exceed 1 mSv), the half-life of the radionuclides that are handled are short and the
quantity of material present is limited, internal monitoring might be carried out to
demonstrate compliance or may be established for other purposes. For workers in
those installations, there is generally no need to evaluate the results of monitoring
measurements using site-specific or material-specific parameters. A typical example
is a nuclear medicine service. If required by the Authorities, the bioassay monitoring
of the technical staff, medical doctors and nurses will be accomplished, using ICRP
standard models, without the need for workplace characterization (e.g. the
determination of AMAD). Other examples might include university or research
laboratories using trace quantities of radioisotopes.
(310) For such routine operations, where a new intake has been confirmed, a
reference evaluation may be carried out with the following default assumptions:
The intake was an acute event at the mid-point of the monitoring interval.
The exposure was via inhalation of material with an AMAD of 5 μm.
Absorption and fA values: the absorption Type or the default specific
absorption parameter values for the known material are as described in this
document. If the compound is unknown, then for those elements where there is
a choice of absorption Types, the Type for ‘unspecified compounds’ should be
used.
(311) Alternatively, where site-specific or material-specific default values are
available and documented, these may be used provided that they are shown to be
appropriate for the process in which the worker was engaged.
(312) If the value of committed effective dose is confirmed to be less than a
previous established low value (e.g.1 mSv), no further evaluation is necessary.
6.2.2 Detailed evaluation of doses
(313) At installations where workers have the potential to be exposed to doses
higher than 1 mSv, or higher than the derived investigation level (e.g. in situations
such as the loss of control of the source), information should be gathered on the
physical and chemical characteristics of the inhaled or ingested radionuclide, as part
of a workplace monitoring programme, and on the time and pattern of intake. This
information may be used to refine the assessment and reduce uncertainties in the
assessed dose. The types of information that may be used in such an assessment are
discussed in section 6.4.
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