Heat transfer within spent fuel canisters: Phase two of an experimental laboratory study

The primary goal of this research was to develop a generalized correlation for convective heat transfer coefficients in rod bundles such as those encountered in the storage and disposal of spent nuclear fuel. The results of the study provide data relevant to design and performance assessment of spent fuel packages as part of the Civilian Radioactive Waste Management Program. In a series of laboratory experiments, heat transfer and temperature distributions were measured in a vertical annulus, and in 3 x 3 and 5 x 5 vertical rod bundles. A correlation was developed relating Nusselt numbers to Rayleigh numbers, radius ratios, aspect ratios, and pitch-to-diameter ratios. In the annulus experiments with a fixed Rayleigh number, an increase in the Prandtl number resulted in a reduction in the Nusselt number. This is inconsistent with findings that have been reported for vertical cavities, and was attributed to curvature effects. The effect of the Prandtl number in the vertical rod bundle experiments was similar to that in the annulus case. Application of a generalized heat transfer correlation to a pressurized-water-reactor fuel-rod bundle predicted maximum rod temperature to within 4 to 14% of results obtained in field tests with a full-scale fuel-rod bundle of 15 x 15 rods. 32 refs., 51 figs., 4 tabs