THERMAL EVALUATION OF TEMPERATURE VARIATIONS FOR PWR FUEL IN THE NAC-STC TRANSPORT CASK

Thermal analyses have been performed to determine the fuel temperature variations that can occur during transport of PWR fuel in the NAC-STC cask. Detailed three dimensional finite element thermal models were used to determine the fuel temperatures. These thermal evaluations were required to determine the peak clad temperatures as well as the variation of the fuel temperature at all locations within the fuel assemblies. All cask components were modeled explicitly with certain aspects of the basket and the fuel assemblies modeled with effective thermal properties. The variation in the fuel temperature occurs not only due to change in the ambient conditions, but also due to the fuel heat decay during the time of the transport of the fuel. To demonstrate the stability of the fuel temperature variation to modeling, a series of parametric studies were performed which considered uncertainties in the material thermal conductivities and boundary conditions. To further ensure that accuracy of the thermal evaluations, a grid convergence study was performed by calculating the Grid Convergence Index following the procedure described in ASME Verification & Validation (V&V) 20-2009. The additional modeling and analyses also confirmed that the analysis solutions are in the asymptotic range of convergence. A description of the modeling process and the results of the fuel temperature responses are presented in the paper.