One of the challenges with developing a waste container solution is firstly in ensuring it meets the very strict design requirements on safety and function, and then demonstrating that, in a worst-case scenario such as a stack of containers falling, that its containment performance will exceed expectations.
Although we have produced prototypes to demonstrate manufacture and production capabilities, we have used in-depth analyses to prove its performance in standard operation and when under stress.
Types of analysis used in the Capsa nuclear waste container development
We used two different approaches to the analysis work undertaken on the Capsa waste container. The first set of analyses were based around normal operational loadcases, looking at how the containers would be picked up, transported and how they could be stacked within the GDF. The second part of the analysis work was specifically aimed at meeting NWS’ specifications around an impact scenario. The requirement is to assess the waste container’s behaviour in the event of a drop from a height of 11 metres – the maximum proposed height of a stack at a GDF.
Impact analysis – expectations
The outcome sought by Nuclear Waste Services in the event of an impact is that the loss of containment shall be minimised and any release
behaviour shall be low, predictable and progressive. The general expectation from any waste container under such conditions is that a gap will inevitably be created between the lid and the body, but this should be contained and kept to a safe level. The objective of Capsa was to realistically model the behaviour of the unique closure design and provide confidence that the bolt-free lid interface can minimise the loss of containment to meet expected standards.
The process of impact analysis work
We opted for LS-DYNA Finite Element Analysis as this has been extensively used to analyse accident scenarios of nuclear waste containers. We also completed an extensive literature study to determine the best practice approach for performing this type of analysis. The impact analysis itself looks at behaviour of the waste package, comprising the container and the grouted wasteform, when dropped from an 11-metre height onto an unyielding surface. We considered how the container would deform and looked specifically at what happens to the lid and how it behaves. In line with this FEA work, we’ve also carried out calculations to determine the release fraction; this looks at how much energy is absorbed into the waste, enabling us to derive the likely fraction of particulate generation, and therefore to compare this with published data for existing waste container design.
Impact analysis has been fundamental in demonstrating that our unique closure mechanism provides not only a safe, remote and efficient closure method, but that it also minimises loss of containment and provides a slow, predictable and progressive release of particulates.