ASUNDER - Adaptable Semiautonomous Underwater Decommissioning Sample Retrieval Robot

There are many legacy sites within the nuclear industry that contain facilities that are submerged, such as the primary contain vessels in Unit 1 of the Fukushima Daiichi Nuclear Power Plant in Japan, and the storage ponds at Sellafield in the UK. These submerged sites often contain, or have contained, highly radioactive materials and as such are highly hazardous. As part of the decommissioning strategy of these facilities, it is necessary to confirm the properties of the materials within these submerged areas, so that they can be removed as safely as possible. Whether it be for validation, or other reasons, at some point it is necessary to remove a small sample of the material for lab-based testing, which may involve determining the mechanical, chemical or radiological properties of the sample. Due to the hazardous nature of the environment, such sample collection cannot be conducted manually. However, robotic systems capable of this task are not available, as most cutting tools for underwater decommissioning were developed for the large-scale removal of structures and hence, are not suitable for the task. Also, these tools often need to be secured to the structure being cut to accommodate the forces generated. This methodology cannot be employed in this scenario.

This project proposes a new solution, whereby an unmanned underwater vehicle (UUV) based robotic manipulator will be used to position and orientate underwater cutting tools to remove samples semiautonomously. Such a system will be able to access almost any submerged environment and retrieve samples where no other system could. This system would mean that the cutting tool will not need to be secured, reducing the need for manual intervention, making the process much safer. Navigation in the turbid conditions caused by particle suspension will be achieved using sonar data presented to the operator using virtual reality. The sonar data will also support imaging systems on the manipulator used to inform and monitor the cutting process locally. The radiological environment will also be assessed concurrently to inform decision making, such as the identification of the corium position or its nature. To achieve this, a novel compact neutron sensor capable of estimating the dose rate and neutron energy spectrum underwater will be developed and integrated.

Additional sensing and feedback systems will be used to monitor the position and orientation of the manipulator joints and end effectors. This will include information about the hydrodynamic loading on the manipulator. An adaptable semiautonomous control algorithm will be developed and implemented based on the inverse dynamics of the manipulator that will compensate for the hydrodynamic forces and the movement of the UUV to ensure the cutting operation continues efficiently. The end effector will incorporate a sample retrieval tool, as well as a cutting tool. This allows the tools to work collaboratively, whilst minimising weight and complexity. It is intended that the control strategy will be adaptable and will allow other tools to be incorporated as required as decommissioning strategies evolve. This system will comprise a complete end-to-end solution, validated in realistic conditions in both Japan and the UK.