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Reduced accidents at UK nuclear power station

09 September 2010

Engineers at a UK-based nuclear power station are using electric-operated pedestrian tugs to assist in the movement of nuclear flasks, a critical stage in the decommissioning of the site. Not only have the tugs provided a cost effective solution to moving the flasks around in very confined spaces, but the risk of handling-related injuries and accidents to staff have also been reduced.

Reduced accidents at UK nuclear power station
Reduced accidents at UK nuclear power station

Located in Dumfriesshire, Scotland, Chapelcross is a four-reactor nuclear power station with a total of eight, 30MW turbines. At full power when operational, the station produced enough electricity to supply every home in South West Scotland, the Borders and Cumbria. The Chapelcross site covers 92 hectares and employs more than 400 people. The station has been undergoing decommissioning since 2004.

Magnox North is the management and operations contractor responsible for the day-to-day operation of the site under contract to the Nuclear Decommissioning Authority. The immediate priority in terms of the phased decommissioning programme is hazard reduction via the safe and efficient removal of all spent nuclear fuel from the four reactors and storage ponds, which is then despatched to Sellafield for reprocessing.
Purchased in July 2009, the two MT20/1500 pedestrian tugs are now being used in two different reactor chambers to pull large, heavy nuclear flasks from the reactors to the flask handling bays. The flasks, which contain spent nuclear fuel, act as shipping containers for transporting the active nuclear materials.

To move a flask from the reactor chamber to the flask-handling bay at Chapelcross, the integrated flask and bogie first need to be guided along the track. The flask then has to be moved to a ‘flask holding area’ (still inside the same secure room) where the lid is torqued on the flask. Until the lid is securely in place, the flask cannot leave this area.

The problem for engineers at Chapelcross is a lack of space in which to manoeuvre the flask and bogie in order to be able to secure the lid in place. The combined weight of the flask, spent fuel and bogie is more than 50 tonnes. The flask holding area immediately outside the reactor chamber is very small (approximately 3.5m2).

Stephen Bennie, Fuel Route Systems Support Engineer at Chapelcross commented: "Prior to investing in the new MT20 tugs from MasterMover, we knew we needed some kind of electric-operated handling system to help us move the flasks around in such a tight space. We did consider the possibility of motorising the bogie system ourselves, but we decided that the cost and time to design, manufacture and install this type of system was prohibitive. We couldn’t use a forklift or locomotive in the flask-handling bay as this area must remain as a radioactive contamination controlled area. Until the lid has been torqued and lid seal pressure tested, only then is a locomotive able to transport the assembly from the building. So we decided to look at alternative solutions."

The MasterTug MT20/1500 was identified as the best tool for the job.

The MasterTug can pull, push and steer wheeled loads up to 15,000 kg, which is sufficient to move the flask and bogie along the guided rails. Traction is the key to moving heavy loads and so the MasterTug is designed to get all the traction it requires by using a coupling system to transfer load weight to the drive wheel. For Magnox North, MasterMover removed the tiller arm from the MT20 and devised a special coupling system between the MT20 and the flask bogie, which enables the machine to be connected and disconnected easily and safely.

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