COVER STORY | DRAGON’S ROBOTIC ROAR
Dragon reactor dismantling roars
The challenge of decommissioning the 20 MW prototype graphite-moderated, helium-cooled Dragon reactor at the UK’s Winfrith site prompted Nuclear Restoration Services to develop a robotic laser cutter for the job.
By James Reed, Dragon Reactor Decommissioning Technical Lead
WINFRITH, LOCATED IN DORSET UK, was constructed in the 1950s as a centre of excellence for nuclear reactor research which laid the basis for the further development of nuclear power. Seven of the site’s nine unique experimental reactors have been removed to date but the final two – Dragon and the Steam Generated Heavy Water Reactor (SGHWR) – are still being decommissioned. Dragon is a prototype 20 MW thermal power output
graphite moderated, helium-cooled reactor with an operating temperature of 1000°C. It tested nuclear fuel and materials to support high temperature reactor programmes at the Winfrith site from 1964 to 1975. At the time it was regarded as one of Europe’s most successful collaborations in applied science and the most important multi-national technical collaboration in nuclear energy. Dragon was the first demonstration of a high temperature gas-cooled reactor and was used as a material test facility to support worldwide high temperature reactor projects. Nuclear Restoration Services (NRS) – a wholly-owned subsidiary of the UK Nuclear Decommissioning Authority – is decommissioning some of the oldest and most diverse nuclear reactor and research sites in the UK, including the Dragon reactor at Winfrith. All present their own unique and complex challenges – different reactor designs, operational functions and ancillary structures to name just a few of the technical issues.
Early decommissioning Work began to remove and dispose of all the reactor plant outside of the reactor pressure vessel in 2011. This included the entire primary cooling circuit, the helium coolant purification system, the fuel loading and unloading systems, spent fuel storage, control rod mechanisms, the top of the reactor pressure vessel and half of the biological shield which was removed to facilitate access to the top of the reactor, as well as the purge gas pre-cooler (PGPC). All the decommissioning that could be carried out without resorting to fully remote operations was completed. The highly irradiated reactor pressure vessel and its contents are the only significant item of radioactive plant remaining in the 100ft (30 metre) diameter cylindrical Dragon building.
Scaling the engineering challenge Although the reactor has been offline for 50 years, the levels of radioactivity are still far too high to send workers in to remove the reactor manually. During construction of the building, a 1.8 metre-thick biological shield wall was created to house the 10 metre-tall reactor and shield building occupants from the radiation. The only access to the reactor now is through the
aperture in the top which had been created during earlier decommissioning work. Access is extremely limited, dark
Above: The Dragon reactor building, Winfrith site 18 | October 2025 |
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