Abstract: As one of the six types of the fourth generation nuclear reactor, lead-based fast reactor (LFR) has unique advantages in power generation, hydrogen production and fuel management. Lead based alloys have high density, good heat transfer performance, high chemical inertness, and hard neutron spectra, which make them advantageous for achieving natural circulation and improving neutron economy when used as fast reactor coolant, providing better safety and reliability for reactors. In order to improve reactor performance and simplify reactor layout, most LFRs are currently designed as a pool type. The main components of the reactor, including the core, main pump, and steam generators, are arranged in the liquid metal pool, so that in the event of a steam generator pipe rupture, high-pressure water from the secondary side may be injected into the liquid metal pool and interact with the lead based coolant, which is called the coolant-coolant interaction (CCI). It’s a physical process of multi-component multiphase coupling. The water is injected into the high-temperature liquid lead bismuth pool under high pressure, and then it is heated to generate bubbles, which are entrained into the core or lead to positive reactivity feedback. In addition, the pressure wave and oscillation of lead pool will also threaten the integrity and safety of the nuclear reactor. Therefore, studying the CCI process is crucial for the overall safety of the LFRs. To study the thermal-hydraulic phenomenon of the interaction between jet water and molten lead bismuth, a small experimental bench of JAEA was modeled and calculated based on the ACENA code independently developed by Xi’an Jiaotong University. And the computational results were compared with experimental data for verification of models in ACENA code. The calculation results show that the ACENA code can conduct the CCI calculation well. After the jet water is injected into liquid lead bismuth (LBE), a cavity is formed. Under the impact of the jet water, the cavity continues to expand. At the same time, boiling occurs at the interfaces. And then the cavity neck is compressed and even closes under certain operating conditions, leading to separation between the upper and lower parts. Finally, as intense boiling occurs, the cavity expands and a large amount of steam is discharged. The series of processes gradually deepen the penetration depth to the maximum value and then drops back. The initial temperature and injection rate of LBE have corresponding effects on the development process of the cavity and the injection depth. The results obtained in this study are of great significance for the thermal-hydraulic analysis of pool-type LFRs under steam generator tubeline rupture (SGTR) accident conditions.