Nuclear decommissioning case study: Sellafield
Sellafield requires a dextrous remote handling capability to conduct safe, cost efficient exploration and characterisation of nuclear facilities. Snake-arm robots are general purpose delivery tools for confined space working in hazardous areas.
The objectives of this project are to demonstrate snake-arm robots in an unstructured, unknown environment performing visual inspection, remote handling, radiological inspection, sampling loose material, water-jetting.
The Sellafield site contains a wide range of ponds, vaults and cells, often containing unquantified radiation risks. Manual entry is not appropriate. A mock-up was built representing a dry processing cell containing pipework and vessels. Access to the cell was via 150mm diameter, 1m long, horizontal and vertical penetrations.
Two snake-arms and a range of tools
Two 2.5m long, 100mm diameter, self-supporting snake-arm robots were constructed. One snake-arm robot was equipped with a water-jetting head - this is the left-hand snake-arm in the image on the right. The second was equipped with a three degree-of-freedom wrist-and-gripper with integrated camera and lights - this is the right-hand snake-arm in the image on the right.
The generic gripper interface allowed a range of tools to be deployed. All tool services were routed inside the snake-arm. Tools included a scoop, a swabbing tool, a radiological probe, a separate inspection camera with optical zoom and lights and of course the gripping jaws of the wrist-and-gripper itself.
The Rail&Rotate linear introduction axis allows the snake-arm to nosefollow into the cell, using either horizontal or vertical penetrations.
Snake-arm nose-following allows the operator to fly the tool using the tip mounted cameras, with the arm following. This intuitive control mode allows the operator to snake between pipes and into vessels.
All tasks were completed in under 4 hours. Arm exchange took less than 15 minutes. The time to change between vertical and horizontal deployment was 45 minutes.