CHF correlation development under ERVC conditions in terms of liquid velocity

Abstract

In-vessel retention (IVR) through external reactor vessel cooling (ERVC) is a severe accident mitigation strategy that is adopted in many light water reactors (LWRs). In the severe accident situation, molten corium gathers at the bottom of the reactor pressure vessel. The ERVC is a method that submerges the reactor vessel by flooding the reactor cavity. The decay heat is removed by nucleate boiling heat transfer at the outer surface of the reactor wall. Critical heat flux (CHF) is a key parameter, which indicates the success of the IVR strategy. A number of papers reported about CHF at the downward facing curved surface. However, previous research have limitations that the CHF models were developed in terms of averaged factors such as mass flux. In this paper, particle image velocimetry (PIV) technique was utilized to measure the velocity field of the fluid in a test section. The test section simulated the gap between the reactor vessel outer wall and the insulation. Air injection was used to simulate CHF conditions in the forced circulation water loop. Curved rectangular channel with 50 cm radius was devised to simulate flow path of the reactor vessel external wall. The channel was made of transparent acrylic. CHF prediction correlation was developed based on the local velocity data acquired from the experiment. The liquid sublayer dry out model was adopted to make the basic form of the correlation.