Research On The Flow Of Coolant Carrying Debris In Fuel Assembly

After a postulated loss-of-coolant accident(LOCA)in pressurized water reactor,a large amount of debris is generated in the containment due to pipe rupture,high-energy fluid injection,and chemical reactions between the coolant and the material in the reactor.The debris is transported with coolant to the containment sump.During the containment sump water recirculation phase,it is inevitable that some debris will pass through the sump screen into the core,causing the blockage of the fuel assembly.If the pressure loss caused by debris in the core is greater than the driving pressure head provided by the reactor,the reactor can't ensure sufficient flow to remove core decay heat.This will destroy the long-term cooling capacity of the core,which may lead to the meltdown of the core.Therefore,studying the influence of debris on the pressure drop of the fuel assembly is of great significance to ensure the long-term core cooling capacity of nuclear power plants after the LOCA accident.This paper focuses on the effect of debris generated after a LOCA accident on the pressure drop across a fuel assembly.The research work in this paper includes experimental research and simulation calculation.The experimental research has carried out the benchmark test,the debris test and the variable flow test on the CAP1400 fuel assembly and the Qinshan NPP fuel assembly(PC8-FA).The simulation is performed using FLUENT software.The porous media model is used to simulate the debris bed formed in the CAP1400 fuel assembly,and the effects of flow rate,porosity,and equivalent particle diameter on pressure drop are analyzed.The pressure drop values of CAP1400 fuel assembly and Qinshan NPP fuel assembly(PC8-FA)at their corresponding debris amount,debris addition mode,debris type and flow rate are obtained experimentally to provide experimental data support for the long-term core cooling capacity of nuclear power plants.The experimental results show that:1)the pressure drop caused by the debris is much larger than the pressure drop of the fuel assembly itself;2)the flow regulation method has an impact on the structure of the debris bed.The comparison between the simulation results and the experimental results shows that the simulation results are in good agreement with the experimental ones in the low flow rate range,and the simulation results differ greatly from the experimental ones in the high flow rate range.The simulation results show that the pressure drop of the debris bed increases with the increase of the flow rate and decreases with the increase of the porosity and the equivalent particle diameter.