Abstract This paper summarizes the existing framework of safety analysis and licensing of Canada Deuterium Uranium (CANDU) reactors in Canada, established by the Canadian Nuclear Safety Commission (CNSC) and discusses challenges with implementing the lessons learned from the Fukushima accident, in the nuclear safety analysis conducted for the existing older and new CANDU reactors. This paper compares the Canadian regulatory requirements with other international nuclear regulatory guidelines, in terms of dealing with Beyond Design Basis Accidents (BDBA) and Severe Accidents, and also reviews the past and present event classification principles in safety analysis, set by the CNSC. The CNSC has published regulatory documents and technical papers outlining the challenges to be addressed with respect to implementations of the Design Extension Conditions (DEC). This paper explores the current requirements and the principles of the regulatory framework in Canada, and discusses practical approaches to determine where in every accident sequence, crediting an Emergency Mitigating Equipment (EME)would be most beneficial, for example, using a portable EME for mitigating the consequences of a Severe Accident, or preventing them. A systematic examination of CANDU Probabilistic Safety Assessment (PSA) results shows that crediting mobile EME in Level 1 PSA accident sequences have challenges and may not be the most beneficial use of EME. While adding another layer of redundancy to backup support systems (electrical power, cooling water or instrument air) further reduces the frequency of a core damage accident scenario, portable EME can only have a short-term mission time, and the main benefit of using them in Level 1 PSA, is to delay the consequences and releases. This paper proposes a thorough review of both Level 1 and Level 2 PSA models and conducting sensitivity analysis results, before making decision on where to allocate EME (i.e., in Abnormal Incident Manuals (AIM), Emergency Operating Procedures (EOP) or Severe Accident Management Guidelines (SAMG). It is crucial to balance between prevention and mitigation of severe core damage and large release frequencies to maximize the safety of the plant and minimize the impact on public safety. Instead of focusing on reducing the probability of occurrence (or frequency) of accidents by allocating every available EME to Level 1 PSA, an alternative approach would be determining where to allocate them to maintain a balance between prevention and mitigation of accidents.

中文翻译：

---

加拿大坎杜反应堆许可框架和紧急缓解设备分配中的安全分析挑战

摘要 本文总结了由加拿大核安全委员会 (CNSC) 建立的加拿大加拿大氘铀反应堆 (CANDU) 反应堆的现有安全分析和许可框架，并讨论了从福岛事故中汲取的经验教训在核安全方面面临的挑战。对现有的新旧 CANDU 反应堆进行了分析。本文在处理超设计基础事故 (BDBA) 和严重事故方面将加拿大监管要求与其他国际核监管指南进行了比较，并回顾了 CNSC 制定的安全分析中过去和现在的事件分类原则。CNSC 已发布规范性文件和技术文件，概述了在实施设计扩展条件 (DEC) 方面需要解决的挑战。本文探讨了加拿大监管框架的当前要求和原则，并讨论了确定在每个事故序列中的哪个位置使用紧急缓解设备 (EME) 最有利的实用方法，例如，使用便携式 EME 进行缓解。严重事故的后果，或预防它们。对 CANDU 概率安全评估 (PSA) 结果的系统检查表明，将移动 EME 计入 1 级 PSA 事故序列具有挑战，并且可能不是 EME 的最有益用途。在为备用支持系统（电力、冷却水或仪表空气）进一步降低了堆芯损坏事故场景的频率，便携式 EME 只能具有短期任务时间，在 1 级 PSA 中使用它们的主要好处是延迟后果和释放。本文建议在决定在何处分配 EME（即，在异常事件手册 (AIM)、紧急操作程序 (EOP) 或严重事故管理中）之前，对 1 级和 2 级 PSA 模型进行彻底审查并进行敏感性分析结果指南（SAMG）：在防止和减轻严重堆芯损坏和大释放频率之间取得平衡至关重要，以最大限度地提高电厂的安全性并最大限度地减少对公共安全的影响。