Multi-Phase Flow Dynamic Analysis Under Large Leakage Sodium-Water Reaction Accident in a Sodium-Cooled Fast Reactor

Abstract The sodium-cooled fast reactor (SFR) is a promising generation-IV design with the nuclear system using liquid sodium as a coolant, high uranium utilization, and a closed fuel cycle. When the double-end-guillotine (DEG) heater tube broke in the steam generator of SFR, a high-pressure and high-temperature hydrogen bubble grew, with a large leakage sodium-water reaction (SWR) occurring. The reaction not only caused the pressure and temperature to increase promptly but also diffused the multi-phase flow (sodium-hydrogen-sodium-sodium hydroxide) into the steam generator and the secondary loop, which threatened the integrity of the secondary loop and the safety of the key equipment, such as the steam generator, surge tank, and protection system. In this study, a Multi-phase hydrodynamic Analysis code for laRge Leak sodIum-water reactioN (MARLIN) calculating one-dimensional compressible multicomponent multi-phase flow with sodium-water chemical reaction was developed. The continuity equation, momentum equation and energy equation were applied to derive the MARLIN model. The hyperbolic-type partial differential equation was solved by the method of characteristic. FORTRAN language was used to develop the code. Critical equipment in the secondary loop model includes the steam generator, surge tank, pump, rupture disks, and primary and secondary discharge accident tanks. The ACENA code results calculating the sodium-air flow were used to verify the multi-phase code. A good agreement was reached between the ACENA code and the MARLIN code. Based on the structure of the sodium-water reaction experiment, the developed model was applied. The tendency of calculated pressure is consistent with the experiment date. The comparison of the results between the MARLIN model and experiment data was performed to indicate the higher accuracy of multi-phase flow dynamic analysis. Meanwhile, the comparison of the calculation between the MARLIN code and the conservation sing-phase code was proposed. It can be found that the multi-phase sodium-hydrogen-sodium hydroxide flow result was more reasonable and accurate in simulating and analyzing the actual large leakage SWR dynamics in the SFR. As a preliminary best estimate code in this study, the MARLIN code is valuable for steam generator design and protection from the large leakage SWR accident in the SFR.