Handling solution helps nuclear decommissioning process

Paul Boughton
A piece of handling equipment devised by Penny Hydraulics has been used at the Dungeness A nuclear power station in Kent, UK, for the past five years to retrieve fuel element lugs from a splitter vault so that they can be sorted for processing.
Dungeness A was commissioned in 1965 and generated power for the national grid for over 40 years before ceasing production at the end of 2006. It is now being decommissioned under the management of Magnox Limited which operates the Magnox Dissolution (MXD) plant. The MXD Plant is a unique plant which dissolves fuel element debris thus reducing the volume of legacy waste. The company is also dismantling various pieces of plant and equipment, demolishing a number of buildings and creating a long term storage facility so that items can be kept in a safe and secure environment.
One of the facilities on site that had to be cleared was a pair of splitter vaults that contained around 30 tonnes of fuel element lugs. These are fin-shaped outer casings of spent fuel elements that had been placed in the vaults after they had been removed from the fuel element outer casing - a process carried out for a number of years during operation but not recently. A number of other small metallic objects with high dose rates, such as springs and thermocouples, had also been placed in the vaults. Magnox Limited wanted to retrieve all the items and sort them for processing and for secure storage.
The vaults are underground and their contents only be accessed remotely. Although Magnox Limited and its main contractor recognised that some form of remotely controlled mechanical handling device would be suitable for the task nothing was available off-the-shelf. The contractor approached load handling specialist Penny Hydraulics to discuss its requirement. The result was innovative handling device that combined existing technologies with engineering innovation and bespoke construction.
Penny Hydraulics proposed a vertical wall-mounted hoist based around the same concept as its popular and proven Cellar Lift. This compact hydraulic lift has been in use in a number of industrial and retail settings for more than twenty years where it has proven to be robust and reliable.
For this particular application the hoist needed to handle the load through almost five metres vertically. The normal carriage and load platform was replaced by a special frame onto which was mounted a compact hydraulic crane. The crane can handle up to 25kg at a reach of over seven metres to access any item inside the vault but has to fold down to enter it from the room above through a small opening. Once inside the crane unfolds and uses either a special petal grab which was manufactured by Penny Hydraulics or a proprietary clamshell grab to capture a batch of lugs which it then holds safely and securely.
The crane folds down and rises from the vault back into the shielded chamber where it places the lugs on to a sorting tray also manufactured by Penny Hydraulics. Working from outside the chamber nuclear technicians use gamma radiation monitors to determine whether each piece of debris should be classed as low or intermediate level waste. Sorted items are then placed in containers for transfer to storage or processing areas.
Identical sets of equipment were supplied by Penny Hydraulics to work in each vault. The company also supplied the controls and power packs so that all handling tasks can be managed remotely. The company’s project management team produced 3D designs and proof calculations whilst ensuring everything had the correct testing and safety certification for this demanding industry.
The equipment was originally expected to remain in use for up to two years. However it has been so reliable and successful that it is still in operation at the Dungeness’s Magnox Dissolution (MXD) plant five years after installation. This facility at Dungeness is still operational and available for use without having to invest in new infrastructure should the need arise. The MXD plant has saved an estimated £35 million during this period based on assessments for disposal, storage and packaging costs of the original volume prior to commencement of the dissolution process being.
Following the success of the installation at Dungeness A, Penny Hydraulics has recently been awarded contracts to provide similar solutions for handling waste items during decommissioning of the Bradwell nuclear power station in Essex and at the Sellafield site in Cumbria. The design and manufacture of the equipment for these new projects will be managed by the company’s newly-formed Nuclear Engineering Division.
For more information, visit www.pennyhydraulics.com

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