The plate type fuel element is widely used in advanced research reactors due to its excellent heat transfer performance, low fuel core temperature and large core power-to-volume ratio, etc. The fuel plate gap is generally 1 to 3 mm, and the aspect ratio is generally greater than 20, thus forming a typical large aspect ratio rectangular channel between adjacent fuel plates. In addition, in the actual research reactor, the distribution of power is uneven along the width of the channel due to the influence of the radiation target and fuel arrangement, which inevitably causes lateral migration and cross-mixing of the fluid. As a result, the flow and heat transfer characteristics may be significantly different from those in conventional narrow channels. At present, the experimental and theoretical research on the flow heat transfer characteristics in the rectangular channel are basically carried out under the condition of uniform heating. It is rarely reported that the flow and heat transfer characteristics in narrow rectangular channel with large aspect ratio under transverse non-uniform heating. Therefore, the numerical study of thermal-hydraulic characteristics in vertical narrow rectangular channel with large aspect ratio under transverse uneven heating is carried out in this study. The numerical calculation shows that the lateral power distribution has a significant effect on the temperature field distribution of the core coolant and the fuel plate, which suggests that the distribution of the lateral power of the plate fuel should be considered in the design and safety analysis of reactor cores.
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