China Experimental Fast Reactor Core Outlet Zone Temperature Distribution

The flow pattern and temperature distribution are very complex in the core outlet region of CEFR (China Experimental Fast Reactor) for the complication of the specific structure and the core arrangement. As a part of safety design and study, detailed analysis and prognostications to the flow and temperature field in this region are the foundation for studying sodium mixing, assessing the effect of temperature fluctuations to control rod guide tubes, and so on. Moreover, it is very necessary to assessing the rationality of temperature monitoring-spot arrangement and the performance of the monitoring, which is of important practical significance for engineering application.In this paper, a 3D numerical modeling to the hot sodium up-chamber of CEFR is set up with the STAR-CD CFD code, and a detailed 3D thermal-hydraulics computations and analysis to the core outlet region are laid heavy stress on. Moreover, the rationality of the temperature monitoring-spot arrangement and the validity of the monitoring to blockage of assemblies are also studied. The main conclusions are following:1. Detailed velocity and temperature distribution under steady-state condition of the 1/4 CEFR core outlet region are obtained. Analysis of the velocity field shows the maximum velocity (about 2.91m/s) presents to interspaces of among assemblies above assembly outlets where sodium flow hasn't adequately developed, and, the next (about 2.58m/s) presents to the top outlets of assembly. Moreover, it is found that a small quantity of sodium flow of non-fuel region enters into fuel region in the not too distant to the assemblies outlet plane; Analysis of the temperature field shows that there are two higher temperature zones both situated in space above peripheral fuel assembly beads, which is corresponding to the assemblies outlet temperature distribution. But, the change of temperature is small in the volume above the assemblies outlet plane and under the central monitoring pole, and the temperature difference is little for adequate mixing in the zone close to the central monitoring pole. In addition, the sodium temperature around the control rod guide tubes always keeps about 542.1℃.2. The rationality of the setting up level of the temperature monitoring-spot, the validity of the monitoring to blockage of assemblies are also evaluated. Relevant computation results and analysis show that the difference between the temperature in monitoring-spot No. 22 and the mean of that of whole fuel zone is around negative 1℃, while the difference between the temperatures in monitoring-spot No. 20, No. 21, No. 18 and the average those of corresponding three assemblies monitored are around positive 1℃. Moreover, the effect of sodium flow besides assemblies monitored to the temperature in monitoring-spots is insignificant. These lead to the conclusion that the setting up level of the monitoring-spot is suitable. In addition, the temperature in monitoring-spot set up at the height of 100mm under 15% blockage of separate assembly is higher than that under its natural state by around 11℃, which indicates that it is valid by and large to diagnose blockage of assemblies by measurement of temperature in those spots.