Preface
This document is the second edition of CSA N288.1, Guide for Calculating Derived Operational Limits of Radioactive Materials in Gaseous and Liquid Effluents during Normal Operation of Nuclear Facilities. It replaces the previous edition published in 1987.
Scope
1.1 Facilities
The previous edition of CSA N288.1 and GSD were to apply primarily to CANDU nuclear power plants in Canada; this guide retains this objective. However, the radionuclides and the environmental pathways they deal with allow it to be applied to releases from many other nuclear facilities, including research reactors, radioisotope reprocessing facilities, waste such as incinerators, as well as power reactors other than CANDU. The radionuclides discussed here (see Clause 4.3) limit application to other types of facilities such as fuel fabrication plants and refineries. On the other hand, neither the radionuclides nor the models discussed in this guide are sufficiently complete to include releases from sources such as uranium tailings, permanent waste management facilities in geological formations and other facilities where complete modeling of pathways in groundwater is required. It is possible to adapt this guide to some needs for similar installations, but it will probably be necessary to use other models or methods for other installations.
1.2 Release routes
The guide deals with releases to the atmosphere and surface waters (fresh and sea water). They do not address releases to groundwater but consider transfers from other media to groundwater wells and ponds. The direct gamma irradiation due to the radioactivity present in the installation is not modeled because it does not imply a rejection.
1.3 Discharge Duration
The methods described in this guide are specifically for low current and continuous emissions. They shall also apply to short-term periodic discharges (see Article 8.2), provided that: (
a) the discharges are controlled and linked to normal operation
b) the rejection rate is roughly the same from one event to the next
(c) the total duration of releases to the atmosphere exceeds approximately 400 hours in the year; at least one or two discharges into the water occur during each month of the year
d) discards occur at random over time
If paragraph (d) is not followed, but if releases are generally known to occur at any given time of the day or year, this guide applies only if the concentrations in the air or water are calculated from meteorological or hydrological data in effect at that time.
Notes:
1) If the calculation of non-random releases is based on timely and relevant data, then the conditions for the frequency of releases can be relaxed.
(2) Discharges that do not comply with these conditions may use another model, including that specified in CAN / CSA-N288.2 for releases to the atmosphere.
3) This article applies to facilities that produce only intermittent releases. Some facilities produce predictably intermittent releases as peaks in a continuous discharge. These releases can be considered as part of current emissions and included in the LOD without special treatment if the total nuclear activity emitted intermittently is approximately 30% lower than the total emissions of the facility. This 30% reduction represents a small fraction of the overall uncertainty of LOD estimates.
1.4 Contaminants
This guide applies to the effects of radionuclide radiation, not the chemicals or chemical toxicity of radionuclides.
1.5 Receivers
The calculation of LODs applies to a representative person with the average characteristics of a group of individuals who, because of their place of residence and lifestyle, may be exposed to the highest exposures to a radionuclide given by a specific source (see Article 4.2). By keeping the release rates well below the LOD, the annual dose received by these individuals (and therefore by all members of the public) will be below the regulatory limits. This guide does not apply to Nuclear Energy Workers (NEWs), or to those who work in a nuclear facility but are not nuclear workers, who benefit from on-site radiation protection programs. The LODs calculated using the models described in this guide are apply only to human evaluation criteria; non-human biota are not affected.
1.6 Minimum downwind distance to be valid This guide does not apply to receivers located near a source subject to turbulence produced by a building, because the atmospheric dispersion model does not simulate the trough that forms from leeward side of the building. Since the trough extends about three leeward building heights, this guide only applies beyond this distance. In addition, beyond a distance of approximately 20 km from the facility, caution should be exercised in the use of the dispersion model, since the assumption of stable weather conditions implicit in the model becomes less valid at greater distances. In practice,
1.7 Regiospecificity
Local parameter values should be used as much as possible to calculate LOD for a specific site. In the absence of local values, the default values provided in this guide for the region near the site may be used. These regional values represent conditions specific to Canada's major nuclear sites (ie, Pickering / Darlington, Bruce, LCR, G-2 and Point Lepreau), but may be considered default values for southern, western and eastern Ontario, Quebec and the Maritime provinces respectively.
1.8 Level of complexity
1.8.1 Simplified approaches
The models described in this guide are complete and include, in some cases, a considerable amount of detail. Such a level of complexity is not necessarily justified for all evaluations. Less complex approaches, implying fewer pathways or details, may be appropriate in some circumstances. A route of entry that clearly contributes very little to the total dose can be ignored. Simplified models such as those described in the IAEA Safety Report Series 19 can then be used, provided that a simplified approach is justified.
Note: It is not necessary, for example, to take into account the following points:
(a) radionuclides that are not emitted by the site in question
(b) pathways associated with wells that are not a source of water for members of the public who live near the site
1.8.2 Default transfer settings
There is a simplified approach to applying this guide without implementing templates. Appendix A lists the default transfer parameters for each radionuclide in each pathway predicted in the model, as well as the assumptions used in calculating the values. If the assumptions are appropriate for the application in question, these default values can be used to evaluate the LODs without implementing the model itself, as shown in Appendix B. This measure allows easy access to the LOD. set of models and parameter values mentioned in this guide. Since the calculation of the default parameter values allowed for conservative assumptions, the LOD values calculated using this approach will be conservative.
1.9
In this guide, the word should indicates a recommendation or what it is advisable but not mandatory to do, and may indicates a possibility or what is permitted.
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