Abstract:
This paper presents the design evaluation of a large concrete cask, originally used for on-site storage of low-level radioactive waste, to meet IP-2 transportation requirements for off-site disposal. The cask, which contains a 9,075-kg concrete monolith inside a concrete shield, was not designed for transportation, so a special lid-retaining device (LRD) was developed to secure the 4,537-kg lid. The core of the evaluation involved using non-linear finite element analysis (FEA) with the LS-Dyna software to simulate the required 1-ft free-drop test conditions. Engineers conducted these simulations to identify the worst-case impact orientation that could potentially dislodge the lid or damage the cask. The FEA included modeling various impact scenarios, such as horizontal impacts and slapdown impacts onto different parts of the cask's buttresses. Although the simulations showed that buttress impacts caused the largest stresses, the analysis indicated that the LRD design would successfully retain the lid and its contents. The findings from the FEA were corroborated by a physical tipover test, which produced a higher impact velocity than a standard drop test. The test confirmed the LRD's effectiveness and also revealed that while some hairline cracks appeared in the concrete, they were insignificant in terms of dose rate increase. This was further supported by a shielding analysis using the SCALE SAS4 code system, which demonstrated that even a large, straight crack would not cause a significant increase in radiation levels. This work highlights how FEA can be effectively used to evaluate complex, heavy packages to meet strict transportation safety standards, supplementing physical testing with detailed stress and strain data.
