Graham Construction has handed over two underground vaults on the site of the former Dounreay nuclear power station.

Cavendish Dounreay Partnership has taken possession of the two new facilities where much of the radioactive waste generated during the clean-out and dismantling of the nuclear reactors, reprocessing plant and other radioactive facilities at the site will be kept.

Low-active waste created during the operation of the site was disposed of in a series of shallow pits, until they became full in the 1990s. In 2003, a consultation was held to decide what should happen with up to 175,000 cubic metres of low-active waste expected to arise during the decommissioning phase or the plant.

In 2009, planning permission was approved for up to six underground vaults adjacent to the eastern perimeter of the site to be constructed which are capable of taking the existing and future low-active waste as more of the site is decommissioned.

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The decommissioning of Dounreay is Europe's largest nuclear site closure project.

As part of the work, Graham was responsible for excavating a total of 243,000 cubic metres of rock during construction of the two vaults. Each vault is equivalent in volume to between 370 and 450 double-decker buses, with the floor 11 metres underground. While a total of 7,600m3 of concrete, 1,330 tonnes of reinforcement and 260 tonnes of structural steel were used during their construction.

Commenting on the project, Leo Martin, Executive Director at GRAHAM Construction said: "The restoration of Dounreay is a massive undertaking and it is tremendously gratifying to play our part in this initiative.

"The challenges involved in designing and constructing the vaults have been considerable, and we would like to recognise the efforts of all the GRAHAM personnel and our supply chain partners who have worked hard to deliver this important project."

Roger Hardy, chairman of Cavendish Dounreay Partnership and managing director of Cavendish Nuclear, the lead partner, added: "Without these new facilities, we could not complete the clean-up and closure of the site, so today's handover is a major step forward in our work to decommission this site and return it to the Nuclear Decommissioning Authority in a condition that is safe for future generations."

The first two vaults and ancillary plant were developed at a cost of approximately £20m, with the total cost of managing the low-active waste through the closure programme is expected to be in the region of £110m.

Subject to regulatory and other consents, the first containers of waste are due to be removed from the site later this year and filled with grout and placed in the vaults. Once each vault is full, it will be back-filled with grout to create a monolithic block that will protect future generations from harm, Graham Construction has said.

(JP/CD)