Validation of fluid-structure interaction calculations in a large-break loss of coolant accident

In the hypothetical LargeBreak Loss Of Coolant Accident (LBLOCA), rapid depressurization of the reactor primary circuit causes loads on the reactor internals. This paper presents numerical simulations of a HDR experiment, where LBLOCA of a pressurized water reactor due to a sudden pipe break in the primary loop was studied. In the experiment, FluidStructure Interaction (FSI) phenomena caused by the flexibility of the core barrel were studied in particular. StarCD Computational Fluid Dynamics (CFD) code and ABAQUS structural analysis code were used for threedimensional calculations. The MpCCI code was used for twoway coupling of the CFD and structural analysis codes in order to take FSI into account. Twoway FSI calculation was also performed with ABAQUS only by modeling water as an acoustic medium. Pressure boundary condition at the pipe break was evaluated with the system code APROS as a twophase calculation. Comparisons with the experiment were made for fluid pressures and break mass flow as well as for structural displacements and strains. Fairly good agreement was found between the experiment and simulation when coupling of the CFD and structural analysis codes was used. For the acoustic calculation, the results showed good agreement in the early phase of the simulation. In the late phase, structural loads were overpredicted by the acoustic calculation due to the effect of bulk flow of water which is not included in the acoustic model.