Safety Analysis of Spent Fuel Transportation Cask of Bushehr Nuclear Power Plant through the Passing of Fire Tunnel with ANSYS®10.0

The spent fuel assemblies (FAs) of Bushehr Nuclear Power Plant are planed to be transported by TK-13 casks. Each spent fuel transportation cask holds 12 spent FAs and has a thick steel container to provide shielding. The calculations have been performed for FAs with burn ups of 60 MWd/kg and a 3-years cooling period. The ANSYS®10.0 general finite element analysis package was selected for this analysis, since it is an analytical tool, widely used for licensing of spent nuclear fuel casks. The selected model included all the significant heat transfer paths within the casks and between the casks and the external environment. The computational model was subjected to the thermal environment of the tunnel during the fire transient using boundary conditions derived from the results of the fire dynamics simulator computational fluid dynamics code. The model of cask constructed in ANSYS®10.0 consists of a detailed 3-D representation of a symmetric half cross section of the spent fuel transportation cask and a complete cross section of the surrounding tunnel wall. In this model, the cask is oriented horizontally within the tunnel. This orientation gives the cask's outer surface the maximum exposure to the highest temperatures in the fire environment. This includes exposure from the tunnel surfaces by thermal radiation exchange and the flow of hot gases generated by the fire, which results in significant convection heat transfer to the package during the fire transient. The results of this evaluation strongly indicated that neither spent nuclear fuel particles nor fission products would be released from the spent fuel transportation cask. The internal temperature of TK-13 cask which was analyzed through the fire tunnel scenario did not reach the level that could result in rupturing of the fuel cladding.