核电站SSC（构筑物、系统及设备）的各项管理要求均以SSC的安全等级为基础。目前基于传统安全分级的管理要求在很多方面表现出过度的保守性，给核电带来了不必要的负担；同时在少数方面也存在过于宽松的情况。因而有了Risk-informed （风险指引）SSC分级思想的产生。本文的研究工作力图建立起风险指引SSC分级的执行框架，以推动此分级思想在我国核电行业的发展，并通过对大亚湾核电站的风险指引分级实例研究，探讨并解决了风险指引SSC分级流程中存在的技术问题。在此研究中进行了下列相关工作，并得到如下所述的结论： 1.在充分调研传统分级体系及风险指引分级产生背景的基础上，通过对传统分级方法和风险指引分级方法的比较分析，得出：现阶段所讨论的风险指引分级并非从根本上替代传统分级，而是根据设备的风险重要性对传统分级方法进行的优化。 2.通过对国际上现有风险指引分级实例的调研、总结和比较，明确了实施风险指引分级的流程。它应包括三个步骤：利用风险排序信息的定量化风险评估过程、基于工程分析的纵深防御评估过程、以及风险敏感性分析。这三个步骤通过层层递进的关系确保了分级结果的合理性和保守性。 3.针对分级流程中的纵深防御评估过程在可操作性上存在的困难，本文提出了一套系统化的、可操作性更强的进行纵深防御评估的改进方法，并解决了其中有关的技术问题。该方法在一定程度上减少了对评估人员主观因素的依赖，提高了结果一致性的保证，有利于此思想的推广应用。 4.采用上述流程，对大亚湾核电站辅助给水系统设备进行了风险指引分级的实例研究。在所研究的重要设备中，有35%的安全级设备可被划分为低安全重要设备。实例研究除了取得上述具有相当参考价值的分级结果外，也达到了验证分级方法可操作性的目的。
The categorization of Structures, Systems and Components (SSCs) is one of the cornerstones in the operation and design of the Nuclear Power Plant. The regulation requirements based on the current deterministic categorization are over-conservative in some aspects, and on the contrary, some other requirements are too loose. In order to make the requirements to reasonable, the Risk-Informed categorization of SSCs has been presented. The objective is to establish a risk-informed SSCs categorization frame work and promote its development in china nuclear energy field. In this paper, the problems in the process of risk-informed SSCs categorization are investigated and solved, based on the pilot study in china Daya Bay NPP, and the results of pilot study were discussed. Major achievements are listed as following: 1.Base on the broad survey information, the difference and relationship between the current categorization and the risk-informed categorization has been discussed. The risk-informed categorization does not replace the existing “safety-related” and “non-safety-related” categorizations. Rather, it intends to optimize the current categorization according to the significance of SSCs. 2.The meaning of risk-informed categorization is investigated based on the contrast between the existing processes in nuclear industry. It is evaluates the risk significance of SSC using an integrated process which includes three steppes: PSA (probabilistic safety analysis) assessment using the importance measures of SSCs, defense-in-depth assessment based on the engineering analysis and risk sensitivity study for results. This three-fold process can make the results reasonable and conservative. 3.The defense-in-depth assessment in the existing categorization process has difficulty in executing in the practice. Therefore, based on the modifying on this disadvantage, a new risk-informed SSCs categorization frame work has been established in this paper, and the technical problems has been discussed and solved. It reduces the influence on the results which comes from the subjective judgments of human and keeps the consistency of the results. This frame work will promote the development of risk-informed SSC categorization in china nuclear energy field. 4.A case study of risk-informed categorization has been developed in Daya Bay nuclear power plant. In the study, the components belong to the auxiliary service water system which are modeled in the PSA have been selected. In the results, 35% “safety-related” components have been re-categorized as low safety significance. This study proves the risk-informed categorization flow is systematic, comprehensive and practicable.
