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Abstract The vertical targets in fusion divertors are the main component which are exposed to very high heat flux generally exceeding 10 MW/m2. In addition, since the heat is non-uniformly imposed to the cooling channels by unique one-side heating, the local heat flux can easily reach up to 20 MW/m2. It is a very challenging engineering target even when considering the latest cooling technology. In this study, CFD-based shape optimization is applied in order to find the optimal channel cross-sectional shape for minimizing local heat flux on the cooling surface. For simplicity, 2-D thermal analysis is adopted as the first step and it estimates preliminary optimized shapes. In this 2-D analysis, heat transfer model is simply reflected on the boundary conditions by analytic method using heat transfer correlations. Then, the optimized shapes are validated using detailed 3-D CFD simulations based on Eulerian two-phase flow models with/without boiling heat transfer. Maximum heat flux on the cooling channel surface is defined as the objective function in the optimization process. Finally, it is found that the maximum heat flux and temperature in the cooling channel can be significantly reduced compared to the original circular channel shape by simple modification to the ellipse-like cross-section. Effects of boiling heat transfer and manufacturability are also discussed in this paper. [ABSTRACT FROM AUTHOR]