Simulator aids upgrade of Sellafield robots

Wednesday, 16 July 2025

The Pile Fuel Cladding Silo (PFCS) was built in the 1950s and is based on the simple design of a grain silo. The concrete structure is 29 metres long, 10 metres wide and 18 metres high and is divided into six tall compartments. It contains irradiated cladding materials removed from fuel assemblies used in some of the UK's earliest reactors at Windscale and Chapelcross. It stopped receiving waste in the early 1970s and now holds more than 3200 cubic metres of intermediate-level waste.

The PFCS was originally designed to remain sealed forever, but equipment has now been installed to enable the safe removal of the wastes so the facility can be decommissioned. Within the silo is a Waste Container Handling Facility, a concrete room where robots process waste containers.

One such robot is a large six-axis industrial robot arm, which unbolts empty containers, sends them to be filled with waste, then securely bolts the returning containers for onward transfer. The arm also swabs the outside of the container to check for contamination and puts the swab in a deposit box for analysis.

Executing pre-programmed tasks is routine. However, when physical upgrades are needed, such as adding new swabbing tools to the robot arm, operators have to take the robot out of service, and suit up in full protective gear to make changes. Changes then need multiple test runs, often with several human re-entries to adjust the setup. Each entry creates risks to human health and risk of damaging the robot, whilst trial runs for new setups create downtime. Even pure software upgrades require downtime while the new programme runs on the robot, monitored by cameras and personnel in the facility.

Simulator developed

Through the PFCS Operational Simulator (OpSim) project, a team from the Robotics and Artificial Intelligence Collaboration (RAICo) has developed a simulation that allows these changes to tooling or operational procedures to be tested and validated in the simulation before deployment into the facility. Once validated, software updates can be transferred digitally to the robot with almost no downtime, and physical updates need far fewer entries to make changes.

RAICo is a collaboration between the UK Atomic Energy Authority (UKAEA), Nuclear Decommissioning Authority (NDA), Sellafield Ltd, the University of Manchester and AWE Nuclear Security Technologies aimed at accelerating deployment of robotics and AI to solve shared nuclear decommissioning and fusion engineering challenges.

The PFCS OpSim project harnessed cutting-edge robotics, purpose-built 3D software, and a team that combined RAICo and Sellafield Ltd expertise in digital technologies and nuclear decommissioning environments.

To map the waste handling facility, a robotic quadruped, Spot, entered the silo with a LiDAR scanner, which uses lasers to collect precise positional data of everything in the space. Those data points were converted into 3D CAD assets, which were used to build a precise digital replica of the PFCS. That was done using RAICo's in-house 3D visualisation software platform, RHOVR (Remote Handling Operations Virtual Reality), which harnesses the Unreal Engine - better known for its use in video games - to create hyper-realistic 3D environments.

Next, an off-the-shelf simulator of the robot's hardware and software was acquired, and integrated into the RHOVR setup – the most technically challenging element of the project – so the team could run robot programmes in a photorealistic virtual environment. Finally, the simulator was validated over six months, before being formally demonstrated at RAICo1 in March this year.

The demonstration was successful and a working version has since been established at Sellafield Ltd's Engineering Centre of Excellence, where it is already being used to execute and verify existing robot programmes in the simulation environment, as well as for providing visual demonstrations of how the PFCS facility operates.

Additional applications

Many Sellafield facilities have similar setups, for example the Waste Transfer Route - the pathway of waste to storage and disposal - uses similar robots in similar sealed rooms for bolting and unbolting waste containers. That opens the door to future projects through the RAICo programme that could adapt the simulator to a wide range of use cases across the Sellafield site.

"This collaboration with RAICo has continued to help Sellafield approach complex robotic operations in hazardous environments," said Rav Chunilal, head of robotics and artificial intelligence at Sellafield Ltd. "By working seamlessly together we've developed a simulator that allows us to test and deploy changes virtually, reducing downtime and risk, and making it safer for our operators. It's accelerating our mission and setting a new benchmark for innovation in nuclear decommissioning which can be repeated across Sellafield and other NDA group operating companies."

NDA Head of R&D Kate Canning added: "This is a great example of a solution that can be deployed across the NDA group, bringing even greater benefits. It demonstrates the value of NDA group's participation in the RAICo programme which is accelerating deployment of transformational technologies across our sites and facilities."

The first batch of waste was successfully retrieved from the PFCS in August 2023 and it is expected to take many years to empty the silo.