Bolt Study – Behaviour of Bolts in Drop Accident Scenarios of the Nirex 3m³ Box ILW Package

The mission of Nirex is to provide the UK with safe, environmentally sound and publicly acceptable options for the long-term management of radioactive materials. One of the key tasks is to ensure that waste is packaged by waste producers in a form which is suitable for safe storage, transport, handling and potential disposal. In pursuit of this key requirement, Nirex has developed specifications to set the standard for the design and performance of waste packages, and has developed standard containers for the packaging of intermediate level (ILW) and some low level waste (LLW) - one of these is the 3m³ Box for immobilised operational and decommissioning ILW. The dimension envelope of this package is 1716 mm x 1716 mm in plan with 430 mm corner radii, 1226 mm tall. The maximum loaded weight is 12 tonnes. A generic design of this container has been developed, which is a welded structure manufactured from austenitic stainless steel (EN 10088-2 steel number 1.4404). The lid is connected to the body by 28 stainless steel bolts [1]. Figure 1 shows a prototype of the box during manufacturing. One of the key principles in the Nirex specifications for performance under normal and accident conditions is that activity release should be low and predictable. For impact conditions, Nirex has developed performance criteria based on drops onto an unyielding target from three heights that are representative of the waste package life cycle: 0.3 m drop - representative of normal handling conditions; 10 m drop – representative of an impact accident while transported within a transport overpack; and 25 m drop – representative of an impact accident within an emplacement facility. The performance criteria are based on activity release of specific sizes of particulates, but not on extent of deformation, or amount of stress or strain in the package, although these will have an effect on the activity release.