前言:这是CSA N288的第四版。1、与核设施正常运行相关的放射性核素环境迁移、归宿和暴露建模指南。它取代了2014年、2008年和1987年出版的前几版，标题为《核设施正常运行的气载和液体流出物中放射性物质衍生释放限值计算指南》。本版本的主要变化包括a）更新了这些指南的结构，以提高CSA N288系列的一致性；b） 从指南中删除行政用语； c） 在用户确定的区域提供额外的澄清；d） 确定了水生植物和无脊椎动物的稳定碳数据；e） 提高整个指南语言的一致性；andf）更新了转移系数指南。COG背景文件（Hart，2013）与第四版一起修订；更新后的版本在下文中称为COG衍生发布限制指南或CDG（Hart，2019）。本指南的使用者应注意，加拿大核设施的选址、设计、制造、施工、安装、调试、运行和退役均应遵守《核安全与控制法案》及其法规。 CSA N系列标准为核设施和活动的管理提供了一套相互关联的要求。CSA N286为管理层提供全面指导，以制定和实施健全的管理实践和控制措施，而CSA集团的其他核标准则提供支持管理体系的技术要求和指导。这些指南与CSA N286一致，不重复CSA N286的一般要求；然而，它们可能会为这些要求提供更具体的指导。范围:1.1设施本指南和CDG适用于加拿大的CANDU核电站。 然而，所涉及的放射性核素和环境途径使这些指南适用于许多其他核设施的排放，包括研究反应堆、放射性同位素处理设施、垃圾处理设施（如焚烧炉）和CANDU设计以外的动力反应堆，但受第1.2条至第1.8条详述的限制。适用于其他类型的设施，如燃料制造厂和炼油厂，受到此处考虑的放射性核素的限制（见第4.3条）。这些指南可能会进行调整，以满足此类设施的部分需求，但其他部分可能需要额外的模型或方法。 然而，这些指南中包含的放射性核素和模型都不足以涵盖铀矿和工厂或永久性地质处置设施等来源的排放。此外，对于需要对地下水路径进行广泛建模的任何设施，这些路径都是不完整的。1.2释放途径本指南涵盖向大气和地表水（淡水和海水）的释放。虽然考虑了从其他介质向地下水井和池塘的转移，但它们并不涉及向地下水的释放。由于设施内的放射性直接伽马辐射不涉及释放，因此未对其进行建模。 1.3排放持续时间本指南中规定的方法适用于常规、连续、低水平排放。它们也适用于定期、短期释放（见第8.2条），前提是a）释放受到控制并与正常运行相关；b） 不同事件的释放率大致相同；c） 对于大气释放，一年中的总释放持续时间超过约1000小时；对于水生释放，一年中每个月至少发生一到两次释放；d）释放随时间随机发生。如果未满足第d）项的要求，但已知排放发生在一天或一年中的特定时间，则仅当使用当时有效的气象（水文）数据计算空气（水）浓度时，本指南才适用。 注:1）如果使用适当时间的数据计算非随机释放，可能会放宽释放频率的条件。2） 不满足这些条件的版本可以使用其他型号，如CSA N288中规定的型号。2.大气排放。3） 对于一些设施，间歇释放可以预测为连续基础释放上的峰值。如果以间歇形式释放的总放射性小于设施总释放量的约30%，则此类释放可被视为常规排放的一部分，并包含在DRL中，无需特殊处理。 30%的截止值被认为是DRL估计总体不确定性的一小部分。1.4污染物本指南适用于放射性核素的辐射效应。它们不适用于化学品或放射性核素的化学毒性。1.5受体该模型可用于计算具有代表性的人的剂量或得出其释放限值，该代表性的人具有一群人的平均特征，这些人由于其位置和习惯，可能受到特定来源释放的给定放射性核素的最高暴露（见第4.2条）。这些指南不适用于核能工作者（新闻），也不适用于非核能工作者- 在核设施工作的新闻，他们被认为受到现场辐射防护计划的保护。使用本指南中规定的模型计算的DRL仅适用于人类受体；然而，这些模型可用于支持非人类生物群的剂量计算。1.6有效下风距离这些指南不适用于靠近受建筑物诱导湍流影响的源的接收器，因为大气扩散模型不模拟建筑物背风面形成的空腔。由于空腔顺风延伸约三个建筑高度，因此这些准则仅适用于超过此距离的情况。 此外，在距离设施约20 km以外的地方，应谨慎使用扩散模型，因为模型中隐含的稳态气象条件假设在距离越远时就越不有效。这在实践中不是一个问题，因为通常会发现代表人员距离设施不到20公里。1.7站点特定在将模型应用于特定站点时，应尽可能使用本地参数值。如果本地值不可用，则可以使用这些指南中为最接近感兴趣地点的区域提供的默认值。 这些区域值代表加拿大主要核电站（即皮克林/达林顿、布鲁斯、CRL、G-2和莱普劳角）的条件，但可分别解释为安大略省南部、安大略省西部、安大略省东部、魁北克省和马里泰晤士河区域的默认值。使现场独特的一些项目包括:地形（如悬崖、河谷、湖泊效应）、靠近水体、盛行的风型和表面粗糙度。1.8复杂程度1。8.1更简单的方法这些指南中规定的模型是全面的，在某些情况下包含相当多的细节。 并非所有评估都需要这种复杂程度。在某些情况下，涉及更少路径和/或更少细节的不太复杂的方法可能是合适的。任何对总剂量没有显著影响的途径都可以忽略。在这些情况下，可以使用更简单的模型，如国际原子能机构第19号安全报告系列所述的模型，前提是提供使用更简单方法的理由。注:例如，无需考虑以下事项:a）未从相关现场释放的放射性核素；和b）与现场附近公众未将其用作水源的水井相关的通道。 1.8.2默认传输参数在不实施模型的情况下，可采用简化方法应用这些指南。附录A列出了模型中每个路径的每个放射性核素的默认转移参数，以及计算值时的假设。如附录B所示，如果假设适用于相关应用，则可使用这些默认值来获得DRL的估计值，而无需实施模型本身。这允许以简单的方式访问这些指南中的所有模型和参数值。由于在计算默认参数值时进行了保守假设，因此使用此方法计算的DRL将比通过实施模型获得的DRL更保守。 默认传输参数也可用于进行初始评估，并结合灵敏度分析，以确定哪些路径或放射性核素值得进一步努力，通过应用现场特定测量来降低模型的不确定性（见CDG，附录J）。1.9本指南中的术语，“宜”用于表示建议或建议但不需要的建议，“可”用于表示选择或指南范围内允许的建议。

Preface:This is the fourth edition of CSA N288.1,Guidelines for modelling radionuclide environmental transport, fate and exposure associated with the normal operation of nuclear facilities. It supersedes the previous editions published in 2014, 2008, and 1987 under the title,Guidelines for calculating derived release limits for radioactive material in airborne and liquid effluents for normal operation of nuclear facilities.Major changes to this edition includea) updated the structure of these Guidelines for increased consistency within the CSA N288 series;b) removed administrative language from the Guidelines;c) provided additional clarification in areas identified by users;d) identified stable carbon data for aquatic plants and invertebrates;e) improved consistency of language throughout the Guidelines; andf) updated the guidance on transfer factors.The COG background document (Hart, 2013) was revised in concert with the fourth edition; the updated version is referred to hereafter as the COGDerived Release Limits Guidanceor CDG (Hart, 2019).Users of these Guidelines are reminded that the site selection, design, manufacture, construction, installation, commissioning, operation, and decommissioning of nuclear facilities in Canada are subject to theNuclear Safety and Control Actand itsRegulations.The CSA N-Series Standards provide an interlinked set of requirements for the management of nuclear facilities and activities. CSA N286 provides overall direction to management to develop and implement sound management practices and controls, while the other CSA Group nuclear Standards provide technical requirements and guidance that support the management system. These Guidelines work in harmony with CSA N286 and do not duplicate the generic requirements of CSA N286; however, they may provide more specific direction for those requirements.Scope:1.1 FacilitiesThese Guidelines and the CDG are intended to apply to CANDU nuclear power stations in Canada. However, the radionuclides and environmental pathways addressed make these Guidelines 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). These Guidelines 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 these Guidelines are complete enough to cover releases from sources such as uranium mines and mills, or permanent geologic disposal facilities. In addition, the pathways are incomplete for any facilities where extensive modelling of groundwater pathways is required.1.2 Release pathsThese Guidelines cover releases to the atmosphere and to surface water (both fresh and marine). They do 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.1.3 Release durationThe methods specified in these Guidelines are designed for routine, continuous, low-level emissions. They also apply to periodic, short-term releases (see Clause 8.2), provided thata) the releases are controlled and associated with normal operations;b) the release rate is roughly the same from event to event;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; andd) 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, these Guidelines apply only if the air (water) concentrations are calculated using the meteorological (hydrological) data in effect for that time.Notes: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 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 estimates.1.4 ContaminantsThese Guidelines apply to the radiation effects of radionuclides. They do not apply to chemicals or to the chemical toxicity of radionuclides.1.5 ReceptorsThe model can be used to calculate doses or derive release limits 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). These Guidelines do 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 these Guidelines apply to human receptors only; however, the models can be used to support dose calculations for non-human biota.1.6 Downwind distance of validityThese Guidelines are 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, these Guidelines apply 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 20 km.1.7 Site specificityLocal parameter values should be used wherever possible when applying models to a specific site. Where local values are not available, the default values given in these Guidelines 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, Quebec, and the Maritimes, respectively. Some items which make sites unique are: topography (e.g., escarpment, river valley, lake effect), proximity to water bodies, prevalent wind patterns, and surface roughness.1.8 Level of complexity1.8.1 Simpler approachesThe models specified in these Guidelines 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 be considered:a) radionuclides that are not released from the site of interest; andb) pathways related to wells that are not used as a source of water by members of the public near the site.1.8.2 Default transfer parametersA simplified approach is available for application of these Guidelines 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 these Guidelines 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.The default transfer parameters can also be applied to conduct an initial assessment, combined with a sensitivity analysis, to determine which pathways or radionuclides merit further efforts to reduce model uncertainty through the application of site-specific measurements (see CDG, Appendix J).1.9 TerminologyIn these Guidelines, "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 the Guidelines.