Experimental study on the circulating-cavity flow and an innovative central baffle design in a steam generator1

Steam generator (SG) is the key equipment in pressurized water reactors (PWR), which transfers heat from primary circuit to secondary circuit and has the feed water vaporized into the steam. It is related to the safe, reliable and economical operation of the nuclear power plant. Many researches have been done on SG, including numerical simulation and experimental research. Since it is involved with complicated steam-water (two phase) flow in high temperature and high pressure, it is not easy to measure the key parameters such as pressure, temperature and void fraction, especially to carry out the visual observation. So the detailed working information of SG such as void fraction and flow pattern is still unknown, while this information is very important for the improvement of SG performance. In order to obtain the working information of SG and study the dynamic flow process in secondary side, a visualization scaled-down mock-up experimental bench was set up. Although its operation parameters (temperature and pressure) are much lower than the actual one in PWR, the internal dynamic flow process of SG in this facility is kept similar to the actual one by the scaling analysis and design. Appling the high speed camera, particle image velocimetry (PIV) and self-made optical fiber probes, two phase flow behavior including flow pattern, velocity and void fraction were collected and analyzed in the experiment. From the experiment, a circulation phenomenon is discovered; which is defined as circulating-cavity flow (CCF). At U-bend area, CCF flows from hot side to cold side, which may result in flow-induced vibration (FIV) and jeopardize the U-tubes. In order to limit CCF, a baffle installed in the middle of U-bend area is proposed to suppress CCF. The experimental results show that this baffle can effectively suppress the CCF. This paper may contribute to the design and safety of SG.