The hydrodynamic loads are very important for the discharge piping design because of the fast opening of the valves and the presence of liquid in the upstream loop seals. Therefore, this work implemented a force balance formulation into the RELAP/SCDAPSIM code to determine the hydrodynamic loads directly. The force balance method, which equates resultant force transmitted from fluid to structural elements as the sum of all pressure and frictional tractions acting on the wetted surface of the element. Then an assessment was performed with RELAP/SCDAPSIM code for EPRI/CE Test No.917, which was a simulation of a hot water loop seal discharge followed by steam discharge through a pressurizer safety valve. In the RELAP/SCDAPSIM calculations, the input data such as valve opening characteristics, initial fluid conditions, system Nodalization, and system component modeling, were based on original RELAP5/MOD1 and RELAP5/MOD3 calculations performed by EPRI. The calculation results were compared with the experimental data as well as the RELAP5/MOD1 and RELAP5/MOD3 calculation to assess the applicability of the RELAP/SCDAPSIM for the hydrodynamic loads calculation. It was demonstrated from the comparisons that the RELAP/SCDAPSIM code with force balance calculation yields very similar hydrodynamic loads to the experimental data as well as the RELAP5/MOD1 and RELAP5/MOD3 calculation results. Therefore, it is recommended that the new force balance calculation implemented in RELAP/SCDAPSIM can be used to calculate the hydrodynamic loads for the hot water loop seal discharge followed by steam discharge transient.

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