Assessment of the sealing system of an ilw transport container in a 9m regulatory impact

UK Nirex Ltd is developing a range of reusable shielded transport containers (RSTCs) to ensure the safe transport of immobilised intermediate level waste to a future UK deep repository for disposal. The RSTCs use an inset lid for mechanical strength and radiation shielding, but the containment boundary is provided by a separate lid seal member (LSM). The LSM is a semi-flexible steel diaphragm surrounded by a rim which carries a double O-ring seal. The LSM rim is clamped to a flat mating surface on the container body. A finite element model has been developed for an RSTC with a wall thickness of 285 mm, in order to assess its containment performance in 9m regulatory drop tests (IAEA 1996). The challenge was to predict the size of small gaps that might appear between the LSM rim and the RSTC body seal face ; this level of detail would be 1-2 orders of magnitude smaller than the displacements experienced in the impact zone. The model was first validated against a series of one-third scale model drop tests of the RSTC. The validated model was then analysed for 9m regulatory impacts in the six worst impact attitudes. The behavior of the LSM was assessed for each attitude and the seal face (gaps) between the LSM and the body were determined. Although small gaps of about 0.5 mm are predicted, it is likely that containment would be preserved. (authors)