Model investigations of the heat transfer from spent fuel assemblies in gas-filled shipping casks

In the transportation of spent fuel assemblies (FAs) special attention has to be focussed on the safe dissipation of radioactive decay heat to the environment in order to avoid impermissible temperatures developing at the shipping cask or the FAs. Because the corresponding safety parameters, that is, the maximum FA and fuel element surface temperatures, cannot, however, be measured directly within the casks, model experiments have been performed in which the 30 WWER-type FAs contained in one shipping cask were simulated by 30 electrically heated rods at a scale of 1:8. The same scale of reduction was used for dimensioning the inner volume of the model cask. The results obtained enable a better qualitative insight into the mechanisms of heat transfer within the shipping cask, including a more precise interpretation of measurable internal temperatures and provide a quantitative description of the radiant heat transfer process. The results can also be applied to 'dry' storage and handling of spent FAs. (author)