Experimental and numerical study for a siphon breaker design of a research reactor

Abstract

For guaranteeing the pool water inventory, which is important to the nuclear safety of a research reactor, a siphon breaker is installed to limit the pool water drain during and after all postulated initiating events in the research reactor. Because the main pipe size of the reactor is relatively large, the size of the siphon break line should be determined to break the siphon phenomena. The siphon breaker design is validated through experiments and numerical simulations. An experimental loop was manufactured at a similar scale of a common research reactor, and a commercially available CFD code was used to compare the experimental results. The undershooting height was measured with a camera and absolute pressure transducer according to the siphon break line sizes. The pressure and superficial velocity inside the main pipe according to the pool water level were analyzed to understand the siphon break phenomena. The CFD code was tested to determine its usefulness for simulating siphon break phenomena over the same conditions with the experiment using several models for the two-phase flow phenomena. The undershooting height, pressure, and liquid superficial velocity were calculated using homogeneous and inhomogeneous models with the SST turbulent model and compared with the experimental results. Although the results of the ANSYS CFD model show some differences with the experimental data, the CFD results using the inhomogeneous model show good agreement with the experimental data. In addition, the homogeneous model results can be used conservatively in the design of a siphon breaker.