Early adopters of nuclear technology face major decommissioning challenges. Many legacy facilities were built with no reference to how they could be safely dismantled and, in many cases, decommissioning is now overdue. Operators are looking for cost-effective techniques, and current and future developments in robotics may provide ways to tackle some of the problematic issues of remote monitoring and handling in contaminated areas.

One innovative British collaboration has led to the development of the LaserSnake, a versatile system which combines laser-cutting technology with a snake-arm robot to offer a valuable addition to decommissioning tools. The LaserSnake is designed to enable a remote-controlled approach to dismantling and decommissioning complex structures in hazardous and confined nuclear environments. It is intended for in situ operation and is particularly suited to working in small to medium sized process cells. A significant feature is that the electronics and controls remain outside the hazardous area while the snake-arm ventures into the danger area.

Laser cutting is a thermal process, where a focused laser beam is used to melt the metal or other material being cut. It is directed by software working from a CAD vector file, or programmed by an operator. The focused cutting beam means that the ‘kerf’ (amount of material removed by the laser) is small in comparison to a blade or cutting edge. A compressed air stream is used to blow away the kerf. LaserSnake uses a commercially available laser unit, capable of producing 5kW of output power down a 200-micron core diameter optical fibre. The cutting tool is a decommissioning specific design, configured to require a minimum of adjustment on site and weighing less than 2kg.

The LaserSnake

The LaserSnake has been developed as a modular arm system with up to four and a half metres of articulation. Its  snake-arm is a continuously curving manipulator which can snake around or over obstacles. It carries an integrated high power laser cutting head, high definition cameras and high-powered illumination LEDs. The tool can be interchanged to give the snake-arm robot the capacity to also carry grippers, environmental mapping sensors and other implements.

Adam Mallion, senior business and project manager at OC Robotics explains the LaserSnake toolbox. “Part of our philosophy with the LaserSnake is a three step process. First enter the environment with a characterisation tool to build up an accurate map, then come back out and take time offline to analyse and plan the next steps before re-entering the cell to perform cutting. For example, you might identify some highly contaminated pipe work that you want to remove, then with the laser tool mounted the operator is able to go back in to that location and selectively cut them out. The final step is retrieval which can be done by using the LaserSnake with a gripper mounted on the tip, or for larger pieces by using the cell crane or an alternative manipulator.”

Collaboration
The LaserSnake is the result of a collaboration between specialist supply chain companies OC Robotics, TWI (formerly The Welding Institute), Laser Optical Engineering and ULO Optics. The Nuclear Decommissioning Authority (NDA), Department of Energy & Climate Change (DECC) and Innovate UK provided funding for development and feasibility work. The National Nuclear Laboratory and Sellafield Ltd have also been involved.

Following a successful feasibility study by OC Robotics and TWI in 2011, the collaborators gained funding for a development project to scale up the technology and ready it for demonstration. During the four-year process, the collaborators set out to ensure the reliability of the technology and materials before its introduction into a nuclear environment. 

Demonstration

In early 2016 the project gained momentum when Sellafield Ltd, which houses some of the UK’s largest and most problematic decommissioning challenges, stepped in to provide the demonstrator project. It uses one of its legacy reprocessing facilities as a general demonstration for new technologies. It is a representative facility which poses a number of typical challenges that the site will face when it enters the decommissioning phase. Sellafield has 350km of piping and over 2000 vessels.

After discussion between OC Robotics and Sellafield Ltd, the snake arm laser cutting technology was tasked with size reducing a large dissolver vessel installed on the eighth floor in the first generation reprocessing plant within Sellafield’s separation area.

Before the laser cutting equipment could be brought onto site the safety case had to be prepared, the infrastructure (filtration unit, compressed air supply, CCTV and lighting) had to be put in place and the facility made ready. Internal stakeholders were consulted and a swathe of required assessments, training and paperwork completed in readiness for the arrival of the demonstrator. 

The deployment mechanism, or garage, which houses the LaserSnake and control is six metres long and one and a half metres in both width and height. There is no room to spare on the Sellafield site and, in order to get it through the crowded separation area and hoisted up to the eighth floor, the garage was transported in three sections. Once in situ these were bolted together against the outside of the cell. When assembled and ready, the robotic arm can snake its way out of the garage and into the cell through the hole drilled in the five-foot thick concrete wall.

During the demonstration project the vessel was precision cut into 175 pieces, each weighing up to 20kg. The equipment was in operation for 48 days.

The cutting operations were successful although there are some lessons learned and further work will be required to improve ventilation arrangements and efficiency of the filters. At the end of the project it was possible to safely remove all the LaserSnake equipment from the site.

Chris Hope, decommissioning capability development lead from Sellafield Ltd, reflects on the outcomes. “The demonstrator project surpassed our expectations. At the outset we had three objectives: to get the laser onto the site, to install it and to fire up the laser and do some cutting. We did all of that within a week.”

After the successful deployment of LaserSnake – which represents the first laser cutting on the site and the first use of snake arm – Sellafield is publicising the technology around the plant in order to identify suitable follow-up projects. Laser cutting of redundant glove boxes is one possibility using either a snake or other robotic arm.

This is an edited version of an article first published in the February 2017 issue of Nuclear Engineering International.