Experimental study on combined reflooding phenomenon and RELAP5 simulation analysis in narrow rectangular channel

摘要

Combined reflooding experiments within narrow rectangular channel were conducted in this article. Conclusions can be obtained that the bottom injection is dominant during cooling process because large amount of top injection is expelled from quenching the heating plate. Besides, the effects of boundary conditions, such as inlet velocity, wall superheat degree, pressure, inlet subcooling and heating power, were compared and analyzed comprehensively. According to cooling curve results, the optimized emergency core cooling method can be determined and the quench front of bottom reflooding arrives almost 225.0 s earlier than certain combined reflooding case.The RELAP5/MOD4.0 code was utilized to simulate the combined reflooding process within narrow rectangular channel, which is very important when large break loss of coolant accident (LBLOCA) occurs. Based on the comparison results of simulation and experiment, the following conclusions can be drawn: RELAP5 code significantly overestimates the heat transfer capacity of film boiling while underestimates quench temperature value; both the pressure difference curves of RELAP5 simulation and experiments have similar tendency during whole process, while the bottom quench front data gradually become divergent in the last stage; besides, the total mass of entrained coolant in combined reflooding case is more than 1.6 kg, while the RELAP5 code still overestimates the entrainment mass.