Background: Through External Reactor Vessel Cooling (ERVC) to achieve the aim of In-Vessel Retention (IVR) is an important severe accident mitigation measure. After the Fukushima nuclear power plant severe accident

IVR-ERVC gains more and more attention. A full-scale IVR-ERVC engineering verification facility REPEC-II was constructed by Shanghai Jiao Tong University. Purpose: To study in-vessel retention by external reactor vessel cooling in large-scale advanced pressurized water reactor under severe accident conditions and meet the demand of verifying the validity of severe accident mitigation. Methods: The flow characteristics of the passages in some parts of the experiment conditions were calculated by RELAP5/MOD3. The natural circulation flow capabilities and features and the typical flashing eruption phenomenon in the experiment on the REPEC-II were preliminarily analyzed. Results and Conclusion: Comparative analysis showed that the calculated results were consistent well with the measured data and visual observation

and basically reflected the reliability of the calculations. Preliminary indication of the flow characteristics of the facility can be further analyzed in-depth

and applied to plan of follow-up experiments. Abstract