One of the major problems encountered in decommissioning nuclear power reactors is dealing with the radioactivity of the components of the reactor. If the parts of a reactor are too hot for human beings to safely handle, then another way must be found. There has been a great deal of work on adapting robots to assist in decommissioning.
The Winfirth site in Doset, U.K. was the location of nine unique reactors and associated facilities. Decommissioning work began in the 1990s. Currenly, there are only two reactors left at the site; a prototype of a steam generating heavy water reactor and the Dragon prototype of a high-temperature gas-cooled reactor. All that is left of the Dragon plant is the reactor core which is contained in a pressure vessel surrounded by thick concreate shielding, steel plates and an outer containment building. The reactor core is scheduled to be removed by 2021. The remaining facility will be demolished by 2022.
Magnox manages the Winfrith site for the Nuclear Decommissioning Authority (NDA). They subcontracted OC Robotics (OCR) to help them remove a sixteen-inch diameter vessel called the purge gas pre-cooler (PGPC) which is attached to the core of the Dragon reactor at one end and extends outside of the concrete and steel shielding of the reactor.
OC Robotics and The Welding Institute (TWI) used funding from the NDA to develop the LaserSnake long-reach snake-arm with laser cutting optics. It has previously been employed at the Sellafield site in Cumbria.
The pipes in the reactor are thick, the layout of PGPC is complex and there is limited access to the PGPC. OCR constructed two mock-ups of the section of the reactor that contains the PGPC in order to test the use of the LaserSnake. When they were confident of their preparations, the LaserSnake was inserted through a small hole in the ten-foot thick concrete shielding around the core of the Dragon reactor. The actual work of cutting away the PGPC took under three hours.
A spokesman for OCR said, “The difficult environment of the external core of the Dragon reactor was an ideal challenge to show the full capabilities of laser-cutting technology and snake-arm robots. Cutting something as thick as the 400mm PGPC with its complex internal geometry had never been attempted before.”
The senior project manager for Magnox said: “We believe this is the first time that laser-cutting technology has been deployed directly on the core of a nuclear reactor. The ability of the LaserSnake to carry out 'keyhole surgery' on the reactor core meant that the work could be carried out using existing protective shielding.”
The head of technology at the NDA said: “This is an excellent example of how early NDA R&D funding support enabled the technology to grow from an exploration of whether laser-cutting could actually be adapted for nuclear into a system that, with further funding and collaborative working, is now mature and being successfully deployed on a number of our sites.”
As more and more of the old nuclear reactors built in the Seventies are permanently shut down, it will be necessary to employ advanced robotics such as the LaserSnake to safely decommissioning them.