RD&D-Programme 2004 - SKB

Conclusions in RD&D 2001 and its review
Kasam says in its review that a great deal of work remains to be done on sealing of the
canister. Further studies should be conducted of FSW and EBW until one of the methods
gives completely satisfactory results. A thorough understanding of the mechanisms that give
rise to defects in the canister must be built up.
SKI says that the documentation of the welding technique for EBW, with regard to both
achieved progress and planned work, is far too scanty and recommends that SKB compile
the results achieved as soon as possible.
Newfound knowledge since RD&D 2001
The results of the development work on EBW have been described in two reports /6-3, 6-4/.
Since 2001, SKB has been working to investigate the mechanisms that give rise to defects in the
weld. This has been done in close cooperation with TWI. Several technical breakthroughs have
been made with regard to generation and control of electron beams as well as process control.
The most important aspects have been development of technology for controlling the electron
beam’s energy distribution, and installation and use of a system to measure and oscillate the
beam.
Due to the parallel development of process and welding systems, the pace of development has
been inhibited by the implementation of untested solutions in the system. This has in turn led to
problems with availability. A programme has been initiated to tackle these problems.
A new type of cathode was developed by TWI in 2002. The goal of the development work
on this cathode was to achieve an electron beam that provides a round weld profile in the root
(the bottom of the beam) and that has a root radius greater than 2.5 millimetres. The risk of root
defects is then minimal. The cathode produced a much better weld profile in tests than before.
The root radius was greater than two millimetres in most cases. Although the goal was not
reached in terms of root radius, the cathode was nevertheless considered to be good enough.
Details concerning cathode design and beam shape cannot be revealed at this time, since TWI
is exploring the possibility of applying for a patent.
TWI has developed equipment for measurement and oscillation of the beam. The equipment
was installed and commissioned in the Canister Laboratory in September 2003. It consists of
a coil for oscillating the beam, a measurement probe, two computers (one for control of the
process and one for collection of welding data), software for control and data collection, plus a
control console, electronics cabinet and cabling between the units. When the shape of the beam
is to be measured, a holder, including a measurement probe on three bars, is mounted on the
coil’s extension into the welding chamber, see Figure 6-3. The control console (see Figure 6-4)
has been replaced with a new, bigger console that has been modified to suit the new equipment.
Figure 6-3. Coil with holder for beam defection.
Figure 6-4. Control console for EBW system.
68 RD&D-Programme 2004