NUMERICAL SIMULATIONS OF TWO-PHASE FLOW IN A FUEL ASSEMBLY OF BLOCKAGE DUE TO LOCA

During a LOCA accident, the debris caused by the action of high energy fluid discharged from the break may transport to the containment sump, then may be entrained into the core by the ECCS water. The debris may cause the blockage of fuel assembly. The air may also enter the reactor with water. Numerical simulations are performed to analyze the air-water flow and particle-water flow through the blocked fuel assembly. The pressure drop in fuel assembly will impact the long-term core cooling capability. The effects of different parameters on the pressure drop over the fuel assembly are analyzed. Pressure drop increases as blockage percentage, mass flow rate or inlet velocity increases for both two-phase flow. The decrease of air volume fraction and the increase of particle volume fraction all cause the increase of pressure drop. Pressure drop increases slightly as bubble diameter increases, and the tiny effect of particle diameter on pressure drop was found as particle diameter varying at an increment of 10um.