October 21-26, 2007, Miami, Florida, USA CONSIDERATION OF ASYMMETRICAL HEAT TRANSMISSION AND DISTRIBUTION USING NUMERICAL METHODS

To demonstrate the compliance with IAEA safety requirements with respect to thermal routine and normal transport conditions, numerical analyses are widely used. Usually, a basic assumption for these numerical analyses is the basket centred in the cavity, which is a safe assumption to calculate maximum temperatures for the parts of the internal arrangement. At least, the vertical or horizontal transport position suggests the consideration of effects due to basket positions out of centre. Those thermal effects are an asymmetrical heat transmission into the cask wall and into lid and bottom respectively. This causes additional temperature stresses for moderator materials or plates at shell, lid and bottom, for instance. An additional effect causing asymmetrical heat distribution is solar insolation, which is stronger in the upper parts of the cask than in the parts facing to the ground. Barriers for casks used to keep temperature limits for the readily accessible surfaces according to §653 of IAEA No. TS-R-1 can create an asymmetrical heat distribution, too. Barriers as canopies, for instance, provide areas around the cylindrical cask with higher and lower convection. In general, the paper investigates the above mentioned effects leading to asymmetrical heat transmission and temperature distribution using numerical analyses methods based on FEA and CFD. The analysis results are compared with experimental results and rather simple analytical approaches. The advantages and disadvantages of the different approaches are demonstrated and discussed. Conclusions are drawn concerning the limitations of these approaches and recommendations for their application are given. The unbalancing effects should be also considered as input data for fire accident analyses according to §728 of IAEA No. TS-R-1. Despite of the fact, that the consideration of canopies or other barriers due to §653 of IAEA No. TS-R-1 requirements are not required by §728. Nevertheless, the paper presents transient calculations to demonstrate this influence.