Research on Approximation Method ofPressurized Water Reactors Fire Risk
压水堆火灾风险近似方法研究
- Tez No: 851666
- Danışmanlar: DOÇ. DR. LİU TAO, DR. Lİ ZHAOHUA
- Tez Türü: Yüksek Lisans
- Konular: Fizik ve Fizik Mühendisliği, Physics and Physics Engineering
- Anahtar Kelimeler: fire, probabilistic safety assessment, nuclear power plant, core damage frequency, NUREG/CR-6850
- Yıl: 2023
- Dil: İngilizce
- Üniversite: Tsinghua University
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 63
Özet
本研究在目前核电厂火灾概率安全评价(probabilistic safety assessment, PSA)方法的基础上，通过简化的数学表达式，为确定核电厂堆芯损伤频率 (core damage frequency, CDF)提供一种近似方法，并为该方法的未来改进提 供建议。 PSA 是一种广泛应用于分析核电站风险信息的技术。基于 PSA 见解，不 断改进设计和提升运行人员表现而有助于持续提高核电站的安全性。火灾 PSA 作为核电厂全范围 PSA 的一部分，可评估三个程度的风险：在第 1 级评 估导致核电站堆芯受损的事故频率; 第 2 级从 1 级堆芯损伤事件开始, 评估导 致核反应堆放射性大量释放的可能性; 第 3 级评估核电站放射性释放对公众伤 害和环境恶化的影响。 NUREG/CR-6850 和 EPRI-1011989 报告概述了开展全面的核电站火灾 PSA 的 16 步程序, 包括每个任务的范围以及流程的每个阶段要遵循的指导方 针。该过程可以通过将核电站进行火灾分区，对分区进行定性和定量筛选，并 评估与潜在的重大火灾场景相关的风险来逐步实施, 是目前世界上广泛采用的 详细评估核电站火灾风险的方法。在目前所开发的简化评估火灾导致堆芯损伤 的频率计算方法中考虑了如下主要因素: 点火频率 (fire ignition frequency, IGN) 、 严 重 因 子 (severity factor, SF) 、 不 可 扑 灭 概 率 (non-suppression probability, NSP)和条件堆芯损伤概率(conditional core damage probability, CCDP)。这些指标表明了火灾事件的特征。对火灾 CDF 的不同因素分别选取 广义值和保守值，可以建立计算整个核电站火灾 CDF 值的简化公式。 本文使用新公式评价了四个不同类型核电厂火灾导致堆芯损伤的风险，将 评价结果 CDF 值与基于所述参数的各种核电厂的历史数据进行比较。结果表 明：利用该公式所得的结果具有包络性，并且通过优化因子值可以进一步提高 评估精度。 关键词：火灾；概率安全评价；核电厂；堆芯损伤频率；NUREG/CR-6850
Özet (Çeviri)
This research will highlight the present level of fire probabilistic safety assessment (PSA) of nuclear power plants (NPPs) and provide an approximation method for determining core damage frequency (CDF) of NPPs by simplifying the presently used expression, as well as a proposal for future improvements of the method and mathematical representations. PSA is a widely used technique for analyzing NPPs risk information. It contributes to the improvement of NPP safety by continuous design modifications and the evaluation of operator performance. Fire PSA, as part of the full-scale PSA of an NPP, can evaluate three levels of risk. Level-1 PSA evaluates the frequency of incidents that result in damage to the nuclear reactor core. Level-2 PSA examines the likelihood of a large release of nuclear reactor radioactivity, beginning with Level-1 core damage events. Level-3 PSA assesses the impact of Level-2 radioactive releases from NPPs regarding public and environmental deterioration. The NUREG/CR-6850 and EPRI-1011989 reports outline a sixteen-step procedure for performing a thorough plant fire PSA. It includes the scope of each task and the exact guidelines to be followed for each phase of the process. An NPP might very effectively undertake the process gradually by dividing the plant into fire compartments, performing qualitative and quantitative screenings of low-risk compartments, and assessing the risk associated with fire scenarios that have the potential to be significant. The CDF is the expected frequency of core damage occurrences per time unit. The following major factors are employed in the currently developed calculation method for simplifying the evaluation of the CDF: fire ignition frequency (IGN), severity factor (SF), non-suppression probability (NSP), and conditional core damage probability (CCDP). These metrics indicate the fire event's characteristics. A simplified formula can be developed to calculate fire CDF values for a whole NPP when the generalized and conservative values are selected for different factors of fire CDF. This research uses the new formula to evaluate the fire CDF in four different types of NPPs and compares the CDF values of the evaluation results with the historical data, plant type and design of various NPPs based on the parameters mentioned. All obtained results show that the results obtained by using this formula are enveloping and prove evaluation accuracy can be further improved by optimization of the factor's values.
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