Dounreay Reactor Core Drilling Success

7th December 2006

Yet another pioneering invention has successfully allowed the crucial next phase of decommissioning Dounreay's Prototype Fast Reactor (PFR) to begin. The innovative purpose built device, which resembles an extremely long flexible drill, enables pockets of liquid metal to be drained from deep inside the redundant reactor.

The fourteen metre long steel drill, required for accessing isolated areas of the reactor core, was designed in-house by UKAEA's specialist design team, manufactured at JGC Engineering's Harpsdale premises, then rigorously tested by the project team at the T3uk trials and test facility in Janetstown, on the outskirts of Thurso.

Operating successfully on the first attempt, the drill was lowered ten metres to align with a very narrow target area between internal components of the reactor. Then lowered a further four metres to reach the surface to be drilled, the drilling rig had an integral camera to assist with accurate positioning, which provided the first visual inspection of the PFR reactor vessel since operations began in the early 1970's.

Ron Hibbert, who managed the project, said: "This shows how some lateral thinking and good team working can solve technical challenges while decommissioning a complex nuclear reactor that was not initially designed with decommissioning in mind.

He added: "Due to the unique and specialist nature of the work being performed, trials and testing is essential, and without the T3uk facility this could simply not have happened and many projects could not have progressed to where they are today."

Releasing sodium from the reactor vessel allows the remainder of the bulk sodium to be treated within the world-record breaking sodium disposal plant which is due to restart this week. This is the latest in a series of innovative initiatives following a strategic decision to release the maximum amount of trapped sodium before the reactor is dismantled, hence reducing future decommissioning challenges and costs.

Dr Jim McCafferty, who is responsible for the PFR decommissioning project, said: "The success of this project is critical to decommissioning PFR. The removal and destruction of the sodium significantly reduces the hazards associated with decommissioning the plant. Safety is the most important aspect of our work and the project team has maintained an exemplary safety record throughout the drilling project. The expert design and planning by the UKAEA design team, led by Calder Bain, has been crucial to the overall success of the project and is a credit to everyone involved."

PFR operated for twenty years from 1974 until 1994, used 1500 tonnes of liquid sodiummetal to cool the reactor core and transfer the heat through three secondary circuits to a steam-generating plant for electricity production. All the nuclear fuel was removed from the reactor following its closure and the next phase of decommissioning is to dispose of the sodium. PFR had the dual role of providing power to the national grid and offering unique research and development facilities. PFR provided information for the future design and operation of large commercial fast reactor stations and had an electrical output of 250 MW, which was enough electricity to supply a city the size of Aberdeen.