Scientists at NPL have deployed their High Accuracy Inspection System (HAIS) to Sellafield Ltd to carry out regular routine inspections of waste stores held at the nuclear site in Cumbria.
HAIS, conceived by NPL, uses digital image correlation technology, a powerful imaging technique, which has previously been used in sectors ranging from rail, aerospace, and oil & gas. HAIS is particularly well suited to monitor the integrity and conditions of different materials.
For many years, encapsulated waste products have been stored at the Sellafield Ltd site and over the next decade retrievals from legacy ponds and silos will generate more. As Sellafield Ltd evolves into a waste management and remediation site the range of waste products is also expected to increase.
It is vital, for safe storage, that a programme of inspection of the waste stores and their key properties is undertaken. However, with many thousands of packages located in engineered stores, it is time-consuming to extract and inspect them all. Therefore, in-situ measurements and deployment techniques are required to demonstrate control, allow appropriate mitigating action when necessary, and reduce dose to workers who currently provide ad-hoc measurement capability.
HAIS can carry out regular inspections up to 16m deep into low-level waste stores. HAIS deploys a camera vertically into an inspection port and takes a series of images inside of the waste storage at pre-determined points. It then uses digital image correlation to analyse previous image sets and quantifies changes over time, including corrosion, movement, vibration and dirt or water ingress.
Areas of concern can then be highlighted and monitored, or a closer inspection carried out since the position is accurately recorded. Using digital image correlation will increase efficiency across the Sellafield Ltd site by enabling very small changes to be detected and far sooner than using traditional manual inspection techniques. The inspection and measurement techniques, enabled through HAIS, uses in-situ automated technologies in dark store environments where traditional communication channels or power sources are absent and allows the detection of signs of unexpected degradation.
There are many benefits of deploying HAIS to monitor and inspect waste stores, including gaining a greater understanding of the evolution of the nuclear materials stored and how it impacts on long term safe storage. For example, measuring the properties of materials in-situ allows for a greater understanding of how much heat is being generated by the material and what the storage system needs to tolerate it. These measurements will ultimately underpin the storage strategy.
For existing stores, HAIS is able to obtain a better understanding of how store environments can change under a range of scenarios for different waste packages. Having accurate in-situ measurements increases the predictability of the environment and therefore helps to infer waste behaviour. The system also provides the tools for monitoring the environment to provide an early indication of deviation from the predicted environment, including temperature, humidity and chloride. Understanding the long-term optimum storage conditions for a range of products enables the system to provide information that could be vital in influencing new store design and improve existing store conditions.
Dr Nick McCormick, Principal Research Scientist, NPL, said: “At NPL we are interested in developing techniques to make measurements less subjective and to minimise human variability. The automation ensures the inspector can concentrate on areas of potential concern and use their skills to efficiently make an accurate assessment of conditions.”
Dr Robert Bernard, Senior Technology Manager, Sellafield Ltd, said: “Sellafield Ltd are happy to be working on introducing new technology to support our mission of reducing the risk of storage of the special nuclear material we’re entrusted with by the nation. Having scientific organisations such as NPL partnering in our work ensures we’re at the cutting edge of deploying practical technology to maintain safe storage.”
18 May 2021