Japan Atomic Energy Agency is now conducting design study and R&D of an advanced loop-type sodium cooled fast reactor. The cooling system is planned to be simplified by employing a two-loop configuration and shortened piping with less elbows than a prototype fast reactor in Japan, Monju, in order to reduce construction costs and enhance economic performance. The design, however, increases flow velocity in the hot-leg piping and induces large flow turbulence around elbows. Therefore, flow-induced vibration of a hot-leg piping is one of main concerns in the design. The flow field in the hot-leg piping is affected by flow disturbance at the inlet, so it is important to evaluate flow field including the upper plenum. In this study, we analyzed unsteady fluid flow by using an integrated model of the upper plenum and the hot-leg piping system. Unsteady Reynolds averaged Navier-Stokes simulation with Reynolds stress model was used for the numerical simulation. The results were compared with experiment results of 1/3 scaled-model of hot-leg piping with the inlet conditions of rectified, swirling and deflected flows as well as simulation results of 1/3 scaled-model of hot-leg piping with rectified flow. In general, the simulation results obtained by using the integrated model show a similar tendency with the experiment results of deflect flows in the downstream region from the elbow exit. The coupling effect of swirling and deflected flows seems to be not significant although further investigation is needed.

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