主泵两相降级对大破口失水事故的影响研究

Research on Effect of Main Coolant Pump Two-phase Degradation on Large Break LOCA

大破口失水事故过程中,主泵的工作范围覆盖了单相液、气液两相和单相气工况。在两相工况下,主泵的扬程和转矩发生降级。对于AP1000核电厂,WCOBRA/TRAC被用于大破口失水事故分析,其现有的主泵两相降级数据来源于西屋W93A主泵。为正确模拟AP1000主泵在大破口失水事故过程中的热工水力特性,需对其两相降级特性进行研究。本研究分别采用国际上广泛使用的SEMISCALE和EPRI/CE主泵的两相降级数据进行AP1000冷段双端断裂事故的计算分析,并与原有W93A的计算结果进行对比。结果表明,AP1000主泵两相降级特性对反应堆冷却剂系统压力、破口流量和安注箱流量影响不大。相比于SEMISCALE和EPRI/CE,现有的W93A的两相降级数据将导致更低的堆芯冷却流量和更高的包壳峰值温度最大值,计算结果相对偏于保守。

During the large break LOCA process,the working range of main coolant pump covers single liquid,liquid-vapor two-phase and single vapor conditions.Under the two-phase condition,the head and torque of main coolant pump degrade.For the AP1000,WCOBRA/TRAC was applied to analyze the large break LOCA and pump two-phase degradation data came from Westinghouse W93 Apump.In order to simulate the thermal-hydraulic characteristics of AP1000 main coolant pump during large break LOCA correctly,the research on the pump two-phase degradation behavior was needed.In this paper,pump two-phase degradation data of SEMISCALE and EPRI/CE were applied to the analysis of cold leg double ended guillotine accident for AP1000,and the results were compared with that of W93 Apump.The results show that pump two-phase degradation characteristics of AP1000 have little influence on reactor coolant system pressure,break flow and accumulator flow.Compared to two-phase degradation data of SEMISCALE and EPRI/CE,current W93 Aresults result in a lower core cooling flowand a higher maximum peak cladding temperature,and thus proves that the results obtained by W93 Adata are more conservative.