A NUMERICAL INVESTIGATION OF NATURAL-CONVECTION HEAT-TRANSFER WITHIN HORIZONTAL SPENT-FUEL ASSEMBLIES

A numerical investigation of natural convection heat transfer is carri ed out for a single, horizontal; spent-fuel assembly in an environment typical of spent-fuel transportation systems as well as some dry stor age/disposal scenarios. The objective is to predict computationally th e convective heat transfer trends for horizontal spent fuel and to com pare the results to data taken in a supporting experimental effort The predicted data consist of thermal and flow fields throughout the asse mbly for a wide range of Rayleigh number as well as numerically obtain ed Nusselt-number data that are correlated as a function of Rayleigh n umber Both laminar and turbulent approaches are examined for a Boussin esq fluid with Pr = 0. 7. The data predict the existence of a conducti on-dominated regime, a transition regime, and a convection regime. Com pared with the laminar approach, a significant improvement in the pred icted Nusselt number is obtained for large Rayleigh numbers when a tur bulence model is employed This lends additional support to the experim ental evidence that a transition to turbulent flow occurs for Rayleigh numbers greater than 10(7). Overall, the numerically predicted heat t ransfer trends compare well with previously obtained experimental data , and the computed assembly Nusselt numbers generally reside within th e range of experimental uncertainty. The predicted thermal and flow fi elds further provide a numerical flow visualization capability that en hances the understanding of natural convection in horizontal spent fue l and allows improved physical interpretation of the experimental data .