DFR Overview
The Dounreay Fast Reactor was a 60 MW (thermal) experimental fast breeder reactor which went critical in 1959.
The vented, highly enriched uranium metal fuel was cooled by NaK, a liquid alloy of sodium and potassium metals designed to remove heat from the core and breeder area of the reactor via two separate circuits.
The reactor has been de-fuelled apart from one stuck experimental fuel assembly and 977 breeder elements, at least 10 per cent of which are jammed or heavily damaged by earlier de-fuelling attempts. The secondary NaK has been removed but the primary NaK is intact, with high levels of radioactive contamination.
The radioactive NaK and associated nine kilometres of reactor pipe work represent one of the most significant hazards at Dounreay. The DFR decommissioning programme is designed to lower the overall hazard by progressive, prioritised removal of hazards:
• Removal of primary bulk NaK by controlled reaction with caustic solution and subsequent abatement of radioactive liquors by specialised ion exchange.
• Removal of individual breeder (and core) elements with specialised remote cutting/grinding/pulling tools and transfer from the DFR sphere to an adjacent treatment and packaging building.
• De-cladding breeder elements, washing and packaging into 500 litre drums for on-site storage as intermediate level waste prior to immobilisation and long term storage.
• Primary circuit decontamination by water vapour nitrogen techniques to oxidise NaK under controlled conditions, passivating the residual reactive metal alloy.
• Size reduction of reactor components by remote techniques and subsequent packaging as ILW and low level waste. This includes the reactor structure and biological shielding.
• Final strip-out of in-sphere components and removal of associated buildings with the exception of specific buildings highlighted by Historic Scotland.
This work requires a range of supporting activities to prepare the reactor sphere, floor area and infrastructure for the major engineering tasks, including extensive electrical systems upgrade, refurbishment of nitrogen supplies, complete ventilation upgrade, strip out of ancillary equipment such as charge machines and cold trap loops and refurbishment of the Goliath crane.
An obsolete fuel storage pond must be emptied and demolished along with a range of minor strip-outs to support reactor decommissioning.
The cost of decommissioning DFR by 2025 is in the region of £240 million.
Construction of the breeder removal facility
Beneath the crane inside the sphere
Construction begins for breeder removal
