DYNAMIC FINITE ELEMENT ANALYSES OF A HLW TRANSPORT CASK WITH POLYURETHANE IMPACT LIMITERS IN 9M DROP TESTS

Between 1990 and 1992 BAM carried out in cooperation with Sandia National Laboratories a series of drop tests with a HLW transport cask equipped with polyurethane impact limiters. In those days test results were analysed with an analytical method to describe the impact limiter behaviour and deceleration-time relationship, which was state of the art at the time. BAM has studied this former test series with the numerical finite element method once more to develop a new analysis method according to present state of the art. These studies show that the analytical results of 1990 were always appropriate and conservative. However, it is possible to study more crush phenomena of the impact limiters and, thus, understand more details of the test results with modern finite element analyses as opposed to analytic calculations. This paper studies not only the influence of the cask axis impact angle on the rigid body acceleration and strain of the cask, but also the influence of the sheet steel properties of the impact limiter. The latter is not negligible because of the comparatively soft behaviour of the impact limiter material. Furthermore, calculations without a damage criterion for the sheet steel are conservative for 9m drop tests. Since damage of the impact limiters appeared during all of these drop tests, calculations with a suitable damage criterion can describe the tests more correctly. Compared to the analytical method of 1990, the expensive dynamic finite element analyses have some distinct advantages. The finite element model, which was verified using more than one drop test, can now be used not only for the explanation of drop test results but also for the design or approval of new polyurethane impact limiters.