Tue, 18 March, 2025
A cutting-edge robotic laser designed at TWI has been used to decommission a nuclear reactor core at Winfrith.
Constructed in the 1950s as a centre of excellence for nuclear reactor research, the Winfrith site laid the basis for nuclear power with nine unique experimental reactors. Seven of these have since been removed, with the final two – the Dragon and Steam Generated Heavy Water Reactor (SGHWR) - now being decommissioned.
The Dragon reactor was a prototype 20-megawatt power output graphite moderated, helium cooled reactor that began testing nuclear fuel and materials in 1964. Defueling in the 1990s was followed by the decommissioning and removal of redundant plant components and equipment from the 100ft diameter cylindrical Dragon building, leaving just the irradiated steel reactor pressure vessel and its core.
The laser technology used to cut the various materials in the reactor’s core was originally tested at TWI, with further testing following with a full-scale mock-up at Winfrith to remove the Purge Gas pre-Cooler. The turn-key laser cutting system designed and developed by TWI is now fully commissioned and operational to dismantle the Dragon reactor, with a similar approach now being considered for other Magnox reactors.
Technical data and learning from these trials were applied to perform keyhole surgery using a snake robot (‘Lasersnake’) to remotely cut the three-tonne Purge Gas Pre-cooler (PGPC) heat exchanger vessel from Dragon’s highly radioactive reactor core in 2018. This was a first for the UK nuclear industry and its success proved laser cutting as the principal technique for reactor core dismantling over the use of alternative hot cutting techniques.
Almost half of the one-inch-thick carbon steel plates that form the Top Ring Thermal Shield have been cut into removable sections using a telescopic mast-manipulator robotic arm and a laser cutter from a control room located outside the reactor building. Once fully removed, this will open up access to the top of the reactor pressure vessel and the core within.
This is the first of eleven planned phases to fully dismantle the Dragon reactor core and pack it into 6m3 concrete intermediate level waste storage boxes. These will then be transported to the Harwell site for storage until the national Geological Disposal Facility is available for permanent disposal.