A computational fluid dynamics (CFD) analysis was performed to predict the transient hydrodynamic loads exerted on the steam generator tubes and the thrust forces on the broken pipe (which is equal to the impingement forces on target structures in the expanding fluid jet path) during a main feed water line break (FWLB) accident at a pressurized water reactor (PWR) power plant. To address a possible severe case of the transient hydrodynamic loads, the break was assumed to occur at the circumferential weld line between the feed water nozzle and the main feed water pipe so that the compressed sub-cooled water would be discharged through the short broken pipe. Thus, a sub-cooled liquid flashing flow through the broken short feed pipe was simulated numerically. Typical results of the prediction were illustrated and discussed. In addition, the present simulation in terms of the transient mass flow rates during the blowdown following the MFLB was compared to other previous calculations. Based on the discussions, the present simulation is considered to be physically plausible and more realistic than other previous predictions.

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