This Guideline and the CDG are intended to apply primarily to
CANDU nuclear power stations in Canada. However, the radionuclides
and environmental pathways addressed make this Guideline applicable
to releases from many other nuclear facilities, including research
reactors, radioisotope processing facilities, waste processing
facilities such as incinerators, and power reactors other than
those of CANDU design, subject to the limitations detailed in
Clauses 1.2 to 1.8. Application to other types of facilities such
as fuel fabrication plants and refineries is limited by the
radionuclides considered here (see Clause 4.3). This Guideline may
be adapted to cover part of the needs of such facilities, but
additional models or methodologies might be necessary for other
parts. However, neither the radionuclides nor the models included
in this Guideline are complete enough to cover releases from
sources such as uranium mines and mills, permanent geologic
disposal facilities, and other facilities where extensive modelling
of groundwater pathways is required.
This Guideline covers releases to the atmosphere and to surface
water (both fresh and marine). It does not address releases to
groundwater, although transfers from other media to groundwater
wells and ponds are considered. Direct gamma irradiation from
radioactivity inside the facility is not modelled because it does
not involve a release.
The methods specified in this Guideline are designed for
routine, continuous, low-level emissions. They also apply to
periodic, short-term releases (see Clause 8.2), provided that
(a) the releases are controlled and associated with normal
(b) the release rate is roughly the same from event to
(c) for atmospheric releases, the total release duration exceeds
approximately 1000 h in the year; for aquatic releases, at least
one or two releases occur in each month of the year; and
(d) the releases occur randomly over time.
Where the requirement of Item (d) is not met but the releases
are known to occur at a particular time of day or year, this
Guideline applies only if the air (water) concentrations are
calculated using the meteorological (hydrological) data in effect
for that time.
(1)Where non-random releases are
calculated using time-appropriate data, it might be possible to
relax the conditions on the release frequencies.
(2)Releases that do not meet these
conditions can use another model, such as that specified in
CAN/CSA-N288.2 for atmospheric releases.
(3)For some facilities, intermittent
releases occur predictably as spikes on a continuous base release.
Such releases can be considered part of routine emissions and
included in the DRL without special treatment if the total activity
released in intermittent form is less than approximately 30% of the
total release from the facility. The 30% cut-off is considered a
small fraction of the overall uncertainty of the DRL
This Guideline applies to the radiation effects of
radionuclides. It does not apply to chemicals or to the chemical
toxicity of radionuclides.
DRLs are derived for a representative person having the average
characteristics of a group of individuals who, by reason of their
location and habits, are likely to receive the highest exposures to
a given radionuclide released from a particular source (see Clause
4.2). By maintaining release rates well below the DRL, the annual
dose to these individuals (and therefore to all members of the
public) will be below regulatory limits. This Guideline does not
apply to nuclear energy workers (NEWs), or to non-NEWs working at a
nuclear facility, who are assumed to be covered by on-site
radiation protection programs. The DRLs calculated using the models
specified in this Guideline apply to human end-points only;
non-human biota are not covered.
Downwind distance of validity
This Guideline is not applicable to receptors located close to a
source affected by building-induced turbulence because the
atmospheric dispersion model does not simulate the cavity that
forms in the lee of the building. Because the cavity extends
approximately three building heights downwind, this Guideline
applies only beyond this distance. Moreover, the dispersion model
should be used with caution beyond an approximate distance of 20 km
from the facility because the assumption of steady-state
meteorological conditions implicit in the model becomes less valid
at greater distances. This is not an issue in practice because the
representative person is usually found closer to the facility than
Local parameter values should be used wherever possible in
calculating DRLs for a specific site. Where local values are not
available, the default values given in this Guideline for the
region closest to the site of interest may be used. These regional
values represent conditions at the main nuclear sites in Canada
(i.e., Pickering/Darlington, Bruce, CRL, G-2, and Point Lepreau)
but may be interpreted as default values for the regional areas of
southern Ontario, western Ontario, eastern Ontario, Québec, and the
Level of complexity
The models specified in this Guideline are comprehensive and in
some cases include considerable detail. This level of complexity
might not be warranted for all assessments. Less complex
approaches, involving fewer pathways and/or less detail, might be
appropriate under some circumstances. Any pathway that can be shown
to not contribute significantly to the total dose may be neglected.
In these cases, simpler models such as those described by the IAEA
Safety Report Series No. 19 may be used, provided that
justification for using a simpler approach is provided.
Note: For example, the following need not
(a) radionuclides that are not released from the site of
(b) pathways related to wells that are not used as a source
of water by members of the public near the site.
Default transfer parameters
A simplified approach is available for application of this
Guideline without implementation of the models. Annex A lists
default transfer parameters for each radionuclide for each pathway
in the model, together with the assumptions made in calculating the
values. If the assumptions hold for the application in question,
these default values may be used to obtain estimates of the DRLs
without implementing the model itself, as demonstrated in Annex B.
This allows all of the models and parameter values in this
Guideline to be accessed in a simple way. Because conservative
assumptions were made in calculating the default parameter values,
the DRLs calculated using this approach will be more conservative
than those obtained by implementing the model.
In this Guideline, "should" is used to express a recommendation
or that which is advised but not required and "may" is used to
express an option or that which is permissible within the limits of
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