UKAEA ^{A World Leader in Decommissioning & Waste Management.}

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Project background

The Windscale Advanced Gas-cooled Reactor was built in the 1950s as the prototype for a family of gas-cooled reactors, providing more efficient energy than previously-used water- cooled reactors. The technology demonstrated by WAGR was then used at seven full-scale reactors, including Heysham, Hartlepool, Dungeness and Hunterston. As such, WAGR was the natural choice for the UK’s demonstration project for power reactor decommissioning.

Key challenges

Our aim was to ensure that WAGR was dismantled safely, predictably and cost-effectively, using existing technology. As WAGR was the lead UK project, we faced unique challenges requiring a high degree of innovation, including a series of core decommissioning campaigns that had to be carried out remotely due to high levels of radioactivity.

Our approach

Since the shutdown of WAGR's operations in 1981, we have made good progress on the decommissioning project. Fuel and associated equipment was removed shortly after shutdown. An intermediate level waste store was constructed along with an encapsulation plant and suitable waste removal route. Four 190-tonne heat exchangers were lifted out and transported to the nearby national LLW Repository at Drigg in Cumbria.

We divided removal of the reactor internals ten separate decommissioning campaigns, each associated with a particular structure. We installed a remote dismantling machine above the core, and active commissioning of the systems was achieved in 1998. Eight of the ten campaigns have already been completed, including dismantling of the 210-tonne graphite core.

Waste is encapsulated in self-shielding concrete waste boxes. All intermediate level waste has been removed from the reactor, conditioned and the resultant boxes placed in the interim ILWstore at Windscale. The self shielding design inhibits dose rates to a level that allows man access for operation and inspection.

Technologies for dismantling the reactor core and associated structures were developed according to campaign requirements. The strategy was to use equipment that is in common use in industry, and adapt it for working in remote environments. In most cases the tools and techniques were trialled on test rigs nearby to prove their safety and effectiveness before being applied on site.

A number of demanding technical challenges have been overcome. Removing the experimental loop tubes was particularly difficult as they had high levels of radioactivity due to their prolonged irradiation in the centre of the core. We worked remotely, filling the loop tubes with grout and cutting them using a hydraulic shear, to reduce radioactive dust. The loop tubes were then stored in high density waste boxes.

The results

WAGR has been a pioneering project and a showcase of engineering excellence that has set international standards for power reactor decommissioning.

The project to remove the core is due to complete by mid 2009. The building will be then decontaminated, the internal concrete structures removed, and finally during 2015 the iconic spherical containment structure will then be removed. Then the reactor site will be remediated as part of the overall Windscale restoration programme.