The challenge
For many years, encapsulated waste products have been stored at the Sellafield Ltd nuclear site, and over the next decade, retrievals from legacy ponds and silos will generate more. As Sellafield moves to waste management and remediation, the range of waste products is also expected to increase.
It is vital that inspection of the waste stores and their key properties is undertaken to ensure safe storage, for example, that no physical degradation has taken place. However, with many thousands of packages located in engineered stores, it is too time-consuming to manually extract and inspect them all. Many packages are stored underwater, presenting a further inspection challenge. Therefore, in-situ measurement techniques are required to demonstrate appropriate store and waste package control, allowing appropriate mitigating action when necessary, and reducing both the potential for human error and the dose to workers who currently provide ad-hoc measurement capability.
The solution
The High Accuracy Inspection System (HAIS), conceived by NPL using its digital image correlation technology, has previously been used in sectors ranging from rail, aerospace, and oil & gas. This a powerful imaging technique is particularly well suited to monitor the integrity and conditions of different materials through sophisticated image analysis. It can also be deployed into a range of hard-to-monitor environments, including underwater and those hazardous to human life, enabling easier and safer inspections.
HAIS was used at the Sellafield Ltd site to carry out regular inspections up to 16m deep into a store on site. Deploying a camera vertically into an inspection port, HAIS takes a series of images inside the waste storage building at pre-determined points. Using digital image correlation to take high resolution images to compare against previous images enables the detection of changes that need addressing or continued monitoring over time. This includes degradation due to corrosion, movement, vibration and dirt or water ingress. For example, measuring the properties of materials in-situ allows for a greater understanding of any degradation mechanism, and what changes need to be made to the storage system in order to tolerate it. NPL’s HAIS software is well-placed to offer this service as it offers continuity of service spanning decades.
The impact
HAIS has enabled Sellafield Ltd to better understand and predict how their store environments can change under a range of scenarios for different waste packages, and how this impacts the storage of the waste. Using digital image correlation enables very small changes to be detected far sooner than traditional manual inspection techniques. Having these accurate in-situ measurements has increased the predictability of the storage environment and therefore helped to infer future waste behaviour and address it appropriately. These measurements will ultimately underpin the storage strategy allowing for areas of concern to be highlighted and monitored, or a closer inspection carried out.
Understanding the long-term optimum storage conditions for a range of waste products enables the system to provide information that could be vital in influencing new store design and improve existing store conditions. The use of HAIS will ultimately lead to safer store and waste package control, and a safer working environment to workers at the site.