熔盐堆堆芯应急排盐系统可靠性分析及优化

Reliability analysis and optimization of core fuel salt emergency drain system for the molten salt reactor experiment

堆芯应急排盐系统作为熔盐堆特有的安全系统,具有排盐和余热排出功能,为熔盐堆提供了一种紧急停堆方式。为定量化分析堆芯应急排盐系统的可靠性,以美国橡树岭实验室的熔盐实验堆(Molten Salt Reactor Experiment,MSRE)为研究对象,使用概率安全分析软件RiskSpectrum建立和计算MSRE堆芯应急排盐系统故障树,得到系统失效概率为5.62×10^(-4),并进行最小割集分析和重要度分析,识别出影响系统失效的关键因素是外套管泄漏失效、控制冷冻阀冷却气的电磁阀共因失效和气动阀共因失效。通过套管换热元件中减少使用焊缝连接,以及采用不同类型部件控制冷冻阀冷却气,可明显降低系统失效概率。分析结果为液态熔盐堆应急排盐系统工程应用研究提供参考。

[Background]Core fuel salt emergency drain system designed for fuel salt drain and afterheat removal,provides a safe shutdown mode for a molten salt reactor(MSR).It has important significance to evaluate reliability of the system for the safety of MSRs.[Purpose]This study aims to quantitatively analyze the failure probabilty of the system and identify the pivotal factors that affecting the system failures,and provide suggestions for optimization of the system in engineering application.[Methods]First of all,the fault tree analysis was employed to model the reliability of the core fuel salt drain system of MSRE through RiskSpectrum software.Then,the minimum cut sets and importance analysis was adopted to identify the most important basic event in fault tree of the system.Finally,two optimization methods,i.e.,reduce the use of welds in bayonet cooling thimbles,and use different types of valves to isolate cooling gas flow of freeze valve,were proposed.[Results]The results show that failure probability of the system is 5.62×10^(−4),and the identified pivotal factors affecting the system failures are welds leakage failures of thimbles and common cause failure of two groups valves of freeze valve.The optimization methods based on results of fault tree analysis can significantly reduce the system failure probability.[Conclusions]This study provides reference value for design and engineering application of the core fuel salt emergency drain system for MSRs.