Improvement of input parameters for the estimation of fuel rod temperature in dry transport cask

A typical PWR spent fuel bundle has a 17 x 17 rod array, and an analysis requires a very long computation time and a vast amount of memory. Therefore, we applied the lumped fuel bundle analysis approach with the homogenized method to estimate the fuel cladding temperature efficiency. Thermal analysis results for lumped fuel bundles showed an excessive radiative heat transfer, and we applied an emissivity modification factor to compensate for this radiation effect. The value of the factor decreased as the number of the rods in the homogenized array decreased.. For the lumped 8 x 8 array, the best emissivity modification factor was shown to be 0.40. The rod emissivity of 0.8 is generally recommended to be used in COBRA-SFS[D. R. Rector et al.] calculations. Therefore, we can use the modified rod emissivity of 0.32 for lumped 8 x 8 array. There are good agreements between the results from lumped 8 x 8 array bundle and the results from real 17 x 17 array bundle. By homogenization, we can increase the computational speed substantially, as well as reduce the requirements on computer memory and space. (authors)