Combination of analytical and numerical methods for the fast thermal evaluation of transport and storage casks

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Dinkel, Christian ; Billenstein, Daniel ; Roppel, Matthias ; Roith, Bernd ; Rieg, Frank:
Combination of analytical and numerical methods for the fast thermal evaluation of transport and storage casks.
2019
Veranstaltung: PATRAM 2019 , 04.08 bis 09.08.2019 , New Orleans, LA, USA.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung , Paper )

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Abstract

Transport and storage casks (T/S casks) for nuclear fuel elements have to fulfil a wide range of requirements, including the safe dissipation of decay heat, among others [1]. In order not to decrease the strength of the used materials, the maximum temperature within the cask has to be limited. Gas filled gaps can have a big influence on the heat dissipation, as their conductivity is much lower than the conductivity of solid materials. At the same time, as convection and radiation exist as further heat transfer mechanisms next to cond uction, fluids are more difficult to consider within Finite Element Analysis (FEA). Due to the small geometrical extents of gas filled gaps in comparison to the overall cask dimensions and the three existing heat transfer mechanisms, FE simulations conside ring such gaps can be very time consuming. Therefore, in cooperation with the Swiss Federal Nuclear Safety Inspectorate ENSI, a simulation tool was developed, which considers the thermal effects of gas filled gaps for the fast thermal evaluation of T/S cas ks. Therefore, analytic al equations are used for a gas filled gap between inner and outer part of T/S casks.
This is done for both upright positioned c asks during interim storage (an nular gap geometry) and lying casks during transport (asymmetric gap geometry). In order to fasten the FE simulation, a special boundary condition called Thermal Gap Condition (TGC) was developed, which is able to consider all heat transfer mechanisms in the gap without meshing it. This is done by using a specially developed Lagrange Multiplier method, which is able to connect parts by using analytical equations. For an annular gap geometry of upright positioned casks it was already shown that fast simulations are possible, whereby radiation was neglected [2]. Now, main focu s lies on asymmetric gaps with an alternating gap width by considering radiation at the same time. This means, a novel TGC is nec essary, as different heat transfer equations have to be applied.