Core makeup tank injection characteristics during different test scenarios using SMART-ITL facility

Abstract The passive injection characteristics of the core makeup tank (CMT) of the SMART (System-integrated Modular Advanced ReacTor) were experimentally investigated using the integral-effect test loop, i.e., the SMART-ITL facility, for three kinds of accident scenarios. These were a small-break loss-of-coolant accident (SBLOCA) with a safety injection line break, a steam generator tube rupture (SGTR), and a feedwater line break (FLB). Several interesting thermal-hydraulic phenomena were found to occur during the accident scenarios. For the SBLOCA scenario, the RCS inventory was reduced and core uncover was a concern. For the SGTR scenario, the pressure barrier that physically isolates the reactor coolant system (RCS) from the secondary system was damaged or broken. For the FLB scenario, the RCS was pressurized for a short time due to a single line failure of the feedwater supply before the passive residual heat removal system (PRHRS) operated. The injection characteristics of the CMT showed typical behavior such as a 3-step phase transition (liquid → mixture of liquid and vapor → vapor) on the pressure balance line and thermal stratification of the CMT inner fluid for all the tests. The phase change mechanism was the same, but the duration of the individual phases differed according to the accident scenarios. It was confirmed that these differences were closely related to the fluid state and temperature of the pressure balance line (PBL), which are affected by the coolant level of the upper down-comer (UDC).