Validation of computational fluid dynamics code models for used fuel dry storage systems

Computational fluid dynamics (CFD) codes have been used to validate the system designs for used nuclear fuel storage and transportation applications. The reliance on and the importance to safety of these codes has grown with the drive to increase the capacity of these systems. The higher capacities of today's designs have increased the total decay heat dissipation from each package from below 10 kW in the 1990's to over 40 kW today. Higher decay heats require more thermally efficient designs to maintain system component and fuel cladding temperatures below their design limits. This results in the need to increase the accuracy of the analytical methods in addition to improving the thermal efficiency. While the use of CFD codes has provided a powerful tool for analyzing the thermal performance of complex designs, the validity of the results provided by the codes are only as good as the numerical models and choices in evaluation options used. In particular, the means used to determine the convective heat transfer coefficients and radiation exchange are critical to accurately predicting the temperature distribution within the storage or transportation system. In the current study, we explore the steps necessary to achieve validation of the FLUENT CFD code against the test results for one of the Transnuclear's used fuel dry storage system and the code's subsequent implementation in the design of another Transnuclear's higher capacity system. These required steps include the choice of meshing scheme, fixed versus temperature dependant thermal properties, choice of turbulence modeling approach and wall function, and the use of steady-state versus transient modeling techniques to capture the turbulent nature of the heat transfer regime. (authors)