Pressure Loss Coefficient of Spacer Grid for a Tight-Lattice Rod Bundle

Experimental and CFD (Computational Fluid Dynamics) analyses were conducted to determine the pressure loss coefficient of a spacer grid for a tight-lattice rod bundle simulating a dual-cooled annular fuel (DCAF) assembly. The DCAF is designed to have both internally and externally cooled channels by adopting annular pellet and dual claddings. The Korea Atomic Energy Research Institute proposed the DCAF assembly for the Korean optimum power reactor (OPR1000) which is a 12×12 square rod bundle with a rod pitch-to-diameter ratio (P/D) of 1.08. The pressure loss across the spacer grid specially designed for the 12×12 rod bundle is required in order to determine the inner to outer cooling channel flow split. Hence, the pressure drop of the spacer grid was measured using the full-size rod bundle for a Reynolds number ranging from 2e+04 to 2e+05. A CFD analysis was also performed to predict the pressure drop of the spacer grid used in the full-size bundle experiment. Only a single grid span of the test rod bundle was modeled in this CFD simulation. The grid loss coefficients by both the experiment and CFD analysis was shown to decrease as the Reynolds number increases. The measured loss coefficient was estimated from 1.30 to 1.50 for the normal operating condition of the reactor core with the DCAF, i.e., Re=3.5e+05. The CFD simulation predicted the grid loss coefficient being approximately 5% higher than the measured value.