(A) two-step thermal analysis method for the assessment of thermal safety of the CANDU spent fuel dry storage canister

Abstract

A two-step thermal analysis method has been developed to evaluate (1) the mean temperature of the CANDU fuel bundles within a fuel basket in a given spent fuel dry storage canister by HEATING5 code with additional input data and heat transfer correlations in the step-1 analysis and (2) the maximum fuel rod temperature within a CANDU 37-element fuel bundle by MAXROT code developed here for step-2 analysis. In addition, the results of sample analysis performed to examine the parametric effects of the specified ambient conditions on the maximum fuel temperature within a canister are presented. Sensitivity studies have been also performed to see the effects of uncertain parameters on the present calculation method. In the step-1 analysis, to solve the entire multidimensional heattransfer problem of the given complex geometry of rod bundles within a canister where three modes of heat transfer, i.e., conduction, convection, and radiation are superimposed using an existing computer code, HEATING5, the geometrically complicated dry storage canister loaded with CANDU spent fuels is replaced by geometrically simpler multiple vertical concentric hollow cylinders having volume and/or mass averaged thermo-physical properties. For the step-2 analysis, on the other hand, to find the maximum fuel rod temperature when the heat transfers among 37 rods in the CANDU spent fuel bundle only by conduction and radiation, the temperatures of the 18 outer-abstract most rods of the CANDU 37-element are assumed to be equal to the maximum fuel bundle temperature obtained from step-1 analysis. For radiative heat transfer these outer-most 18 rods are regarded as an equivalent cylindrical enclosure where no net radiative heat transfer occurs, whereas for conductive heat transfer between fuel rods the heat transfer is assumed to occur through rectangular inter-rod paths. The comparison between the results of step-1 analysis and the mock-up test shows that they are in good agreement. A brief su...