Experimental investigation on steam sparger and its effect on steam contact condensation in makeup tank

The Hualong pressurized water reactor (HPR1000) utilizes a secondary passive residual heat removal system (PRS) to maintain the core in a safe state within 72 h after a plant blackout incident (SBO). Two emergency make-up tanks (EMT) are incorporated into the PRS to provide safe injection to the secondary side of the steam generator (SG). However, during the early stages of PRS operation, direct contact condensation (DCC) of steam in the EMT can cause injection flow oscillations, thereby delaying the EMT safe injection process. The transient experiment was conducted on the integral test facility ESPRIT to study the DCC and injection flow oscillation characteristics of the EMT. Furthermore, the steam sparger was designed and installed on the inlet of the EMT to study its mitigation effect on the injection flow oscillation. The test results reveal that the DCC in the EMT brings about the water hammer and prevents gravity injection. The sparger transfers the momentum of the ingress steam from vertically to horizontally and the saturation layer formed at the steam-liquid interface is therefore well preserved. The injection flow oscillation is thus suppressed. After the sparger is installed, the average injection flow rate is higher than that in the original condition by 3.4 %, and the pressure is slightly lower than that of the original condition by averaging 0.08 MPa. The marginal improvement introduced by the sparger can facilitate system depressurization and improve PRS safety performance.