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

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Project background

GLEEP (Graphite Low Energy Experimental Pile) was the first reactor in Western Europe, built in 1946. GLEEP was initially used to investigate how to make a reactor work and later as an international standard for materials testing and calibration. It was closed in 1990 after 43 years in operation.

Key challenges

Our job was to decommission GLEEP by removing the fuel, over 11,000 fuel canisters and other external equipment. This would allow dismantling of the 13,500-block graphite core, enabling final decommissioning and regeneration of the land.

Defuelling was a key challenge – GLEEP had only been refuelled once in 1960, so our knowledge and experience of how it would be done was limited.

Our approach

We started initial decommissioning – removing the spent fuel – in 1994. This process accounted for 99% of the inventory of radioactive materials in GLEEP.

To defuel the reactor, we designed and commissioned a specialist remotely-operated crane. The fuel removal machine had a 4-point lift crane, which moved on rails between the graphite core and the bioshield. Fuel was discharged by manual rodding from the opposite face of the core, which loaded the spent fuel into trays in the retrieval unit. The retrieval unit then posted the fuel through the bio-shield into a shielded cell, where it was moved into storage cans and despatched to the waste store. The control rods from the core and other external equipment were removed in 1995.

The final stage of decommissioning took place in 2003-2004. We removed the 525-tonne core brick by brick, using a tap and drill machine that lifted the graphite blocks out of the reactor. The blocks were checked for contamination and then processed for safe disposal. During the dismantling, the ‘train track’ that runs through the core was exposed – this was used during reactor materials testing experiments. We removed it in sections, checked it and sealed it for disposal.

By carrying out extensive waste characterisation we were able to dispose of most of the waste in a more environmentally- friendly way. This also had the benefit of huge cost savings.

Finally, we demolished and removed the 1.5-metre thick concrete bioshield, together with activated concrete from the floor-slab.

The results

We completed defuelling within the timeframe and budget, with minimal dose rate to operators. The final decommissioning and dismantling project was delivered four months ahead of schedule and under budget. The RAF hangar that housed GLEEP has been demolished and the area remediated, releasing land for regeneration of the eastern area of the Harwell site.