In this paper, by using the CFD method, the efforts have been tried to conduct the investigation on the subcooled flow boiling in the first wall channel of Water cooled ceramic breeder (WCCB) blanket for CFETR. The detailed 3D distribution of temperature and vapor in the flowing passage have been presented under the heat flux of 0.5MW/m2 and 1MW/m2, respectively. Due to the high heat flux from plasma, the vapor distribution in the channel decreases from the plasma side to the breeder side along the radial direction. Undoubtedly, the volume fraction of vapor increases along the flowing direction because of the heating. Besides, the distribution of the channel wall along the toroidal direction presents the U-shaped tendency. As demonstrated by the results, the vapor is more likely to be generated at the corner of the square channel, and this can easily cause the Critical Heat Flux (CHF), which will destroy the structural integrity and materials melting. To avoid the enrichment of vapor in the corner, the optimization on the flowing channel has been performed by smoothing the corner. The results show that the volume fraction of vapor can be effectively decreased compared with the original square channel. Moreover, from the perspective of thermal hydraulics, the circular tube is the optimized channel which can not only avoid the concentration of vapor, but also can decrease the peak volume fraction.

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