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Internal cask content collisions during drop test of transport casks for radioactive materials
(2013)
In transport casks for radioactive materials, significantly large axial and radial gaps between cask and internal content are often present because of certain specific geometrical dimensions of the content (e.g. spent fuel elements) or thermal reasons. The possibility of inner relative movement between content and cask will increase if the content is not fixed. During drop testing, these movements can lead to internal cask content collisions, causing significantly high loads on the cask components and the content itself. Especially in vertical drop test orientations onto a lid side of the cask, an internal collision induced by a delayed impact of the content onto the inner side of the lid can cause high stress peaks in the lid and the lid bolts with the risk of component failure as well as impairment of the leak tightness of the closure system. This paper reflects causes and effects of the phenomenon of internal impact on the basis of experimental results obtained from instrumented drop tests with transport casks and on the basis of analytical approaches. Furthermore, the paper concludes the importance of consideration of possible cask content collisions in the safety analysis of transport casks for radioactive materials under accident conditions of transport.
Three drop test campaigns have been performed with DN 30 Protective Structural Packaging (PSP) developed by DAHER NUCLEAR TECHNOLOGIES GmbH for the transport of natural, enriched and reprocessed uranium hexafluoride (up to 5 wt%) in 30B cylinders.
The mechanical prototype testing is intended to demonstrate that the package DN30 complies with regulatory requirements under normal and hypothetical accident conditions of transport (NCT, ACT) relevant to IF, AF and B(U)F packages, respectively.
The paper includes the results of the latest test campaign carried out in 2015-2016 at the drop test facility of BAM, Germany with new full scale prototypes of the DN30 PSP and 30B cylinders. Repetition of drop test sequences became necessary after changing to Polyisocyanurate foam as shock absorbing material with variable foam densities. Furthermore, the mechanical behavior of the UF6 content of the 30B cylinder is now simulated by a mixture of cement and steel grid as modified surrogate material; instead of small steel balls. The behavior of this new content simulation is assumed to be more realistic with respect to the properties of real UF6.
Three drop test campaigns have been performed with DN 30 Protective Structural Packaging (PSP) developed by DAHER NUCLEAR TECHNOLOGIES GmbH for the transport of natural, enriched and reprocessed uranium hexafluoride (up to 5 wt%) in 30B cylinders.
The mechanical prototype testing is intended to demonstrate that the package DN30 complies with regulatory requirements under normal and hypothetical accident conditions of transport (NCT, ACT) relevant to IF, AF and B(U)F packages, respectively.
The paper includes the results of the latest test campaign carried out in 2015-2016 at the drop test facility of BAM, Germany with new full scale prototypes of the DN30 PSP and 30B cylinders. Repetition of drop test sequences became necessary after changing to Polyisocyanurate foam as shock absorbing material with variable foam densities. Furthermore, the mechanical behavior of the UF6 content of the 30B cylinder is now simulated by a mixture of cement and steel grid as modified surrogate material; instead of small steel balls. The behavior of this new content simulation is assumed to be more realistic with respect to the properties of real UF6.