Abstract

This study proposes an interpolation-based response surface surrogate methodology to manage a large number of scenarios in dynamic probabilistic risk assessment. It adopts the shape Dynamic Time Warping algorithm to cluster the interpolation neighborhood from time series sample data. The interpolation method was adapted from Taylor Kriging to allow a reduced-order model of the Taylor series. In order to demonstrate its applicability to complex issues in risk assessment for nuclear engineering, an example risk response surface to estimate emergency core cooling system (ECCS) criteria for triplex silicon carbide (SiC) accident-tolerant fuel was constructed. The response surface was exploited to estimate the cumulative failure probability of the fuel cladding structure due to the uncertainties in operator actions and safety systems. The functional failures were assessed based on a combination of individual layer failures computed by coupling Risk Analysis Virtual Environment software with a pressurized water reactor 1000-MW(electric) RELAP5 model and the in-house fuel performance assessment module. Results showed that SiC cladding failure probability spiked less than 1 min after a large-break loss-of- coolant accident whenever the current ECCS criteria for Zircaloy-4 (Zr-4) cladding was used. However, it still provides an increased safety margin of three orders of magnitude compared to Zr-4. This positive margin could be utilized to relax active ECCS requirements by allowing deviations of up to 450 s in its actuation time. The proposed surrogate methodology generated a response surface of SiC cladding failure probability reasonably well, with a significant savings of computation time. This methodology is expected to be useful in the analysis of system response with complex uncertainty sources.

摘要

这项研究提出了一种基于插值的响应面替代方法，以管理动态概率风险评估中的大量情况。它采用形状动态时间规整算法对时间序列样本数据中的插值邻域进行聚类。插值方法改编自Taylor Kriging，以允许使用Taylor级数的降阶模型。为了证明其适用于核工程风险评估中的复杂问题，构建了一个示例风险响应面，用于估计三层碳化硅（SiC）事故容忍燃料的应急堆芯冷却系统（ECCS）标准。由于操作员动作和安全系统的不确定性，利用响应面来估计燃料包壳结构的累积失效概率。通过将风险分析虚拟环境软件与压水堆1000兆瓦（电）RELAP5模型和室内燃料性能评估模块耦合而计算出的单个层故障的组合，对功能故障进行了评估。结果表明，每当使用当前的Zircaloy-4（Zr-4）熔覆层ECCS标准时，一次大断裂冷却液损失事故后，SiC熔覆层失效概率在不到1分钟的时间内就会达到峰值。但是，与Zr-4相比，它仍提供了三个数量级的增加的安全裕度。通过允许最大450 s的驱动时间偏差，可以利用该正余量来放宽主动ECCS的要求。拟议的替代方法可以很好地生成SiC覆层失效概率的响应面，大大节省了计算时间。这种方法有望在分析具有复杂不确定性源的系统响应时很有用。