Analyses of ACME integral test results on CAP1400 small-break loss-of-coolant-accident transient

CAP1400 has been developed as a new passive safety and generation III + reactor based on AP600/1000 technology. Like previous reactors, the small-break loss-of-coolant-accident (SBLOCA) is still one of the most important safety problems that have to be considered before it's widely applications. Although extensive theoretical and experimental results of SBLOCA have been reported in previous studies, the dominant SBLOCA transient mechanisms and the important thermal hydraulic phenomena have not been clearly explained, especially in the passive safety system, due to the complexity of the passive safety nuclear reactor geometry coupled with the transient two-phase fluid interactions. In this study, a new constructed thermal hydraulic integral effect test facility, named as advanced core-cooling mechanism experiment (ACME), which is designed and constructed for supporting CAP1400 safety review, was used to investigate the SBLOCA transient in passive safety plants. 1-inch, 2-inch and 8-inch cold leg breaks and a double-ended direct-vessel-injection (DEDVI) line break were selected as the critical and essential SBLOCA tests. The system pressure, injection flow rate, core level and fluid temperature were considered as the safety related parameters to investigate the system responses to the SBLOCA. In addition, the conditions that affect the SBLOCA chronology were investigated as well. Also, a few important thermal hydraulic phenomena observed in the ACME SBLOCA test were reported, and their effects on the transient were analyzed. The dominant SBLOCA transient mechanisms in the passive safety system were presented. This study not only helps to improve the understanding of SBLOCA mechanisms and important thermal hydraulic phenomena in passive safety systems, but also sheds some lights on SBLOCA analysis, test facility scaling, safety performance evaluation, code simulation and even the design optimization for the passive safety PWRs.