Getting innovation into decommissioning3 March 2017
Decommissioning a nuclear facility is an extremely costly and technically challenging project to undertake. However, advances in technology are leading to new and innovative practices as Penny Hitchin reports looking at the use of LaserSnake.
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.
Snake-arm robots are dexterous devices ideal for working in restricted and contaminated spaces. Cameras and cutting or gripping tools can be mounted onto the snake-arm while its electronics, controls and operators remain outside the confined and hazardous area. Operators rely on high definition camera images transmitted from within the cell by the snake-arm’s cameras to enable precise control of inspection and dismantling work.
The LaserSnake has been developed as a modular arm system with up to four and a half metres of articulation. Its sinuous 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 enables new techniques
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.
The control electronics for the robot are housed outside the hazardous environment with only the arm deployed into the workspace. The snake-arm is driven by wire ropes and controlled by OC Robotics’ proprietary software. The sophisticated software means the snake-arm can map, monitor and manoeuvre around remote complex geometries. The company’s development work over a four-year period culminating in the demonstration project led to advances in snake-arm material and design development to make it more robust and to upgrade its weight-bearing capacity. The snake-arm length was doubled, the total curvature of the arm was increased to over 180 degrees and payload capacity increased from five to 20kg. Ropes and materials for the different parts of the arm were investigated and improved. The actuators and motors were subject to rigorous testing to ensure they would operate over an extended period of time. Such enhancements all supported the safety case.
Two cutting heads were designed for the snake-arm by ULO Optics, one water-cooled, one air-cooled – both with innovations in diffractive optical elements to extend the depth of focus of the cutting beam and allow thicker materials to be cut with a greater stand-off tolerance. The optics have been used with both five and 10kW laser sources, using 200 micron core diameter optical fibres to transmit the beams.
Major advantages of laser cutting include its flexibility and relatively small standoff distance, but the technology must be proven before it is accepted for use in the risk-averse nuclear industry. TWI has been building up laser cutting processes and equipment since 1967. Its first deployment of laser cutting on a nuclear site took place in 2013 at Hinkley Point A where it was used to size reduce contaminated skips. This involved setting up an on-site facility to receive the skips, whereas the LaserSnake is designed to operate in situ and carry out work within process cells.
The snake-arm can carry a tool to conduct laser mapping of the environment. Using this point cloud data (PCD) acquisition approach more accurate laser cuts can be planned. The PCD data is converted into a CAD format compatible with industrial robotics to determine the sequence of cuts.
Ali Khan, principal project leader in the Laser and Sheet Processing Group at TWI, identifies one of the features that makes LaserSnake such a powerful potential tool as the development of one single laser tool able to cut different materials and varying thicknesses up to 210mm. “This minimises waste and makes the technique very adaptable,” he points out, adding that laser cutting has great potential for reducing nuclear decommissioning costs.
The demonstration project
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.
The dissolver was approximately three meters tall, with a diameter of half this and a weight of around five tonnes. It was a double skinned tank made from 32mm rolled stainless steel, with a 12mm outer jacket separated by a 40mm air gap from the main body on the lower portion of the vessel.
Some earlier work had taken place to lower the vessel to floor level and cut into three large sections, but size reduction was required to remove the materials from the cell. Radiological conditions in the cell are categorised as C3 / R4, thus operator access was possible in PVC suit and respirator and the cell layout was well understood.
Before the laser cutting equipment could be brought onto site the safety case had to be prepared, the infrastructure 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 programme of work for Sellafield Ltd’s Active Demonstration team included making the cell laser light safe and installing infrastructure including a mobile filtration unit, compressed air supply, electrical distribution, CCTV and lighting. The snake- arm’s access to the cell was by a hole drilled into the concrete cell wall.
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 wall.
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.
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. Sellafield Ltd gives figures for the programming time as 120 hours, the cutting time as 45 hours. It estimates that 66m of metal were cut at an average speed of 80mm/min.
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.
Chris Hope’s role is to seek new technology which is a high technology readiness level and bring it to the site for testing to see if it has potential applications. He’s enthusiastic about the potential for future use of LaserSnake to reduce
the time and cost of some of Sellafield’s decommissioning challenges.
“This particular project has been the most exciting that we have delivered. It has been a step up in terms of complexity and challenge that we faced. It has been the most rewarding, has received the most interest and has the most potential benefit. It’s been a fantastic project to be involved in.”
Technology Readiness Level (TRL) is a measure used to assess the maturity of evolving technologies (materials, components and devices) before they are market-ready. TRL 1 is basic research, TRL 2-3 is feasibility research, TRL 4-5 is development, TRL 6 is demonstration and TRL 7-9 is about system development and operation. The LaserSnake development project has enabled the device to reach the latter stages and is now market ready.
Introducing innovation into a highly regulated risk-averse industry can be slow. In the UK the NDA has been calling on
the supply chain to deliver innovation to make decommissioning more efficient. The LaserSnake proves an interesting case study showing how with some support, small, specialist suppliers can collaborate to produce innovative solutions to large problems.
Combining lasers with robotics is in its infancy. The LaserSnake demonstrates how the innovative technology can be used to work in hard to reach areas, potentially cutting decommissioning costs and timescales. Its developers are currently seeking new projects and its application is likely to extend well beyond the UK. All the companies involved in the demonstration believe that there is much potential for future development.