Experimental Investigation on Bottom Reflooding in Tube Channel

The reflooding is a key stage in the loss-of-coolant accident (LOCA), and the flow and heat transfer characteristics during reflooding are critical for the development of LOCA analysis code. Although various researches were carried out to investigate the reflooding thermal hydraulics since the 1960 s, the fundamental physical mechanisms involved in reflooding are still not well understood due to complex heat transfer behaviors and flow regimes. Quench temperature is a critical parameter to reflect the effectiveness of core cooling during reflooding. The research on quench temperature also has great importance to the design of fuel rod and the analysis of LOCA. However, the effects of basic physical factors such as initial wall temperature, inlet liquid temperature, inlet velocity and heating power during reflooding on quench temperature are still unclear. Tube channel, annular channel, bundle channel and narrow rectangular channel are commonly used as test sections during experimental study of bottom reflooding. In this study, the thermal-hydraulic behaviors of bottom reflooding in the tube channel were investigated with the range of inlet liquid temperature from 3 cm/s to 15 cm/s, inlet subcooled temperature from 15 ℃ to 75 ℃, initial peak wall temperature from 340 ℃ to 600 ℃, pressure from 0.2 MPa to 0.4 MPa, and heating power from 1.3 kW/m to 2.3 kW/m, respectively. The hydraulic diameter and the length of the tube channel are 12 mm and 1.5 m, respectively. Six temperature measurement points were arranged along the external surface of tube channel with the axial height of 185, 335, 485, 635, 785 and 935 mm from the inlet of heated section. The temperatures were measured using N type armored thermocouples. The mass flow rate was obtained using coriolis type mass flowmeter. The pressures were acquired with pressure transmitters. The test section was heated by modular power supply. The experimental data were collected and recorded using NI acquisition module. Quench temperature and quench time were acquired based on wall temperature curves with double tangent method. The effects of initial wall temperatures, inlet liquid temperatures, inlet velocities and heating powers on bottom reflooding were analyzed based experimental data. The results show that the quench time and quench temperature increase with the increasing of initial wall temperatures, inlet liquid temperatures, and heating power, but decrease with the increasing of inlet liquid velocities. The experimental data presented in this study provide the experimental basis for the development of quench model and the further analysis of physical mechanisms during reflooding. © 2022, Editorial Board of Atomic Energy Science and Technology. All right reserved.