Subchannel thermal mixing is predicted downstream of two different spacer grid designs with and without mixing vanes using subchannel thermal hydraulic and CFD codes. The predicted subchannel temperatures at the end of the spacer grid span were compared to 5×5 rod bundle subchannel temperature measurements occurring at the end of the test section with uniform axial power shape. For the subchannel code, the Thermal Diffusion Coefficient was varied until a best fit was obtained to the subchannel temperature data for single phase flow conditions. After optimizing the Thermal Diffusion Coefficient, good agreement was observed between the subchannel thermal hydraulic code and the CFD code temperature predictions as well as the measurement data. The good agreement between CFD code predictions and test data suggest that CFD tools could replace 5×5 rod bundle mixing tests for single phase thermal hydraulic conditions.
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