Cooling time and CHF enhancement of reactor vessel cooling process by flame sprayed porous coating in different orientations

Abstract

External reactor vessel cooling (ERVC) is an effective strategy to achieve in-vessel retention (IVR) under severe nuclear plant accidents. Earlier transition from film boiling to nucleate boiling can lead to faster cooling and the critical heat flux (CHF) of the reactor pressure vessel (RPV) determines the success of IVR-ERVC. In this study, a porous coating of 316L was prepared on the surface of SA508 steel by flame spraying. Quenching experiments of plain surface and coating surface were performed to investigate the enhancement of reactor vessel cooling process at atmospheric pressure in saturated deionized water by using a variable orientation quenching device. The orientations of all experimental surfaces were varied between 0°(downward) and 90°(vertical). The experimental results show that the cooling time of coating surface was reduced by more than 56% compared with plain surface, which is mainly due to the reduction of duration in film boiling phase and the early appearance of Leidenfrost point (LFP). The CHF of coating surface achieved about 30% enhancement compared with plain surface in all orientations. In addition, the cooling time decreased and CHF increased with the increase of orientation because the bubbles separation was easier in the larger orientation angle. The visualization of cooling process was conducted in the vertical orientation and demonstrated that there were more nucleation sites of bubbles and the bubbles grew and separated faster in coating surface.