An experimental study on natural circulation flow characteristics under passive IVR-ERVC conditions

Abstract

In vessel retention (IVR) of molten core debris via water cooling at the external surface of the reactor vessel is an important severe accident management feature of advanced passive plants. During postulated severe accidents, the heat generated by the molten debris relocated to the lower head of reactor pressure vessel needs to be removed continuously to prevent vessel failure.Besides the local critical heat flux (CHF) of outer wall surface which is of the first importance, a stable feature of natural circulation flow and an effective natural circulation capability within the external reactor vessel cooling (ERVC) channel tend to be rather crucial for the success of IVR. Under this circumstance, a full-height ERVC test infrastructure, reactor pressure vessel external cooling II test facility (REPEC-II) was designed and constructed in Shanghai Jiao Tong University (SJTU). During test campaign on the REPEC II facility, the one-dimensional natural circulation boiling flow characteristics with the experimental observation and measurement are investigated under IVR-ERVC conditions.Based on the abundant results acquired in the test campaign, it is attempt to evaluate the ERVC performances and trends under various practical engineered conditions in this paper. From this study, the following conclusions can be made: The influence of different power shapes on the two-phase natural circulation flow is not obvious, while the impact on the resistance characteristics of the outlet section is very significant. Among all the test conditions (power shapes, subcooling, flow path configuration and water level), the resistance characteristics of the outlet section change the most compared with other sections. It is expected that these conclusions may help designers to have a reliable estimate of the impact of some related engineered factors on real IVR-ERVC performance.