Experimental Study on Reflood Behavior in PWR with Upper Plenum Injection Type ECCS by Using CCTF

Abstract

An experimental study of Cylindrical Core Test Facility (CCTF) tests was performed to investigate the reflood behavior in PWR with upper plenum injection (UPI) type ECCS. The major conclusions are as follows: 1. The ECC water injected into the upper plenum fell down to core smoothly and flowed from the core to the downcomer.2. This falling water flow rate was much higher than the predicted with a correlation developed on the base of the small-scale experimental results, i. e. Bankoff's CCFL correlation. This is considered to be because the steam flows up from the core in a limited cross section and separately the water downflow region is formed.3. The steam from the core was condensed by the ECC water in the upper plenum. The hydraulic behavior in the primary system was significantly different if the complete condensation was attained or not.4. For a UPI test with no failure low pressure coolant injection (LPCI) pump simulation, the complete condensation was attained, the water stagnated in hot legs and steam generators, and almost no fluid flowed through the primary loops. For a UPI test with single failure LPCI pump simulation, the complete condensation was not attained, and the steam with entraining the water flowed through the primary loops.