Study Of Flow Field Characteristics In Rod Bundles With Laser Diagnostic Technique

Nuclear fuel assembly is the core component in the nuclear reactor system,which is actually fuel rod bundle with spacer grids and some other structures. And the flow field in the parallel sub-channels has great influence in the heat transfer phenomena of the fuel assembly such as the DNB and Burn Out phenomena, which is the primary thermal consideration for fuel design. Flow field need to be predicted accurately enough to give a better simulation for temperature field. When heat transfer phenomena coupled with flow is properly modeled, can we then consider the multi-physics coupling model for the solution of challenges in nuclear power industry.Single phase flow in rod bundles is the experiments have been conducted to investigate the flow field characteristics. With the aid of high speed camera and high power intensity laser,Particle Image Velocimetry, the whole field non-intrusive and instantaneous measurement technology, is applied to give an insight of the flow field inside the rod bundles. And the experimental rod bundle flow channel is based on the real pressurized water reactor fuel assembly,the same structure and the same diameter. To satisfy the requirements for application of the laser diagnosis technique,matching index of refraction technique is used by the FEP tubes serving as the rod bundles, whose refraction index is the same as the water’s refraction index. In the rod bundle flow channel, there is three mixing vanes spacer grids in the flow channel. And the test section for measurement is after the second mixing vanes grid.The PIV data includes the stream-wise cross section and lateral cross section. The PIV experiment data is compared to results both from other experiment and CFD simulation. Typical velocity profile and similar flow structure are observed, such as dual vortex structure in sub-channels; for results from simulation of rod bundles with the same space grid as the PIV experiment, PIV results is quantitative well matched with given engineering consideration.While some difference should be pointed, and most of these located in the near wall region, that is worth for detailed research further. Besides the comparison mentioned above, flow characteristics of lateral flow field is investigated, including the secondary flow intensity,turbulence statistics data, the vorticity and swirl factor. And dual vortex structure is still visible at the height of Z=20mm, fully developed turbulent flow field resembles even at different flow rates.In order to evaluate results of the PIV experiments,PIV error analysis is performed in this paper, based on the model proposed by Visualization Society of Japan, PIV technique used in the experiments into account, with error propagation theory, a quantitative PIV experiment data error is given, error sensitivity along with other parameters is also analyzed .