nuclear waste
Image: [Oleg Fedotov]©123RF.com

Scientists at the National Physical Laboratory (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, to monitor the integrity and conditions of different materials.

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Dr Nick McCormick, a principal research scientist at 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.”

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. Waste products are expected to increase further, as Sellafield Ltd evolves into a waste management and remediation site.

In order to ensure safe storage, 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.

How HAIS works

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. Here, traditional communication channels or power sources are absent and HAIS allows the detection of signs of unexpected degradation.

Using HAIS will provide a greater understanding of the evolution of the nuclear materials stored and how it impacts 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.

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.