Sellafield supplier reengineers plant arm gaiter

31 January 2011

UK-based engineering firm Beakbane has developed new protective covers that make it easier, cheaper and safer to service the equipment used to handle hazardous radioactive material.

Sellafield vitrification plant manipulator arm with improved gaiter
Sellafield vitrification plant manipulator arm with improved gaiter

The covers, known as gaiters, are fitted to the slave end of the master-slave manipulators (MSM) – large robot arms – that are used to handle radioactive materials during activities such as the disposal of nuclear waste and the processing of nuclear fuel. The gaiters reduce the amount of radioactive contamination the arms pick up in service and hence reduce the amount of decontamination required if they have to be removed for repair or servicing.

For most applications, Beakbane supplies flexible polyurethane gaiters that provide the ease of use and durability required.

In the Magnox and Thorp vitrification plant, the presence of heat and chemicals makes it even more hostile. In these conditions, polyurethane gaiters can become embrittled and tear, so contaminating the slave arm.

Working closely with Sellafield engineers, Beakbane developed a replacement gaiter made from woven cloth which is bonded to a layer of aluminium foil. This is mechanically stronger than the previous material and can also withstand the changes of temperature.

The gaiters are around 1.5m long and 300mm in diameter and are split into two parts. At one end they incorporate an O-ring that forms a seal on the slaves gearbox down to its farthest point called the wrist, a fabricated bellows that allows the arm to extend and retract. All the parts are designed in CAD and cut out on a CNC machine before being assembled to form the completed gaiter, using special processes that ensure a 100% leak-tight seal.

The new gaiters have now been successfully trialled for over a year in real working conditions and adopted as standard equipment. Now, as each polyurethane gaiter in the vitrification plant reaches the end of its service life, it is replaced with one of the new aluminised glass cloth gaiters.

The first of the new gaiters have already been in service twice as long as their predecessors with no sign of deterioration and will not need replacing as long as the slave manipulator arm remains in service, Beakbane said.




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