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Electron beam welding of fuel bundles

Case Study

Electron beam welding is widely employed in the manufacture of fuel bundles. In one such production application TWI were able to help a Member company who had problems aligning the beam with the joint line.

The problem occurred because many welds were made to join together a multi-channelled Zircalloy assembly some 1.2m long and 300mm wide. The welds were in 5mm section and it was necessary to employ a defocused beam to ensure that weld spatter was minimised at the root. The number and width of welds in the workpiece caused it to distort such that after the first few welds the beam had to be steered down a curvilinear path to follow the joint. Viewing and correcting for joint misalignment was difficult for the operator and missed joint defects occurred.

TWI fitted a seam tracker device that measured the beam to joint misalignment and corrected for it as the weld was being made. The device rapidly swept the welding beam out of the weld pool and across the joint line ahead of the weld, at a rate that avoided surface melting. The back-scattered electron signal was collected and analysed to identify the position of the joint and the beam position corrected using the deflection coils.

After fitting the device, welds could be made more simply with a higher degree of quality and consistency.