Frequently Asked Questions
TWI has developed for SKB (the Swedish nuclear fuel and waste management company) two candidate processes for sealing thick-walled copper canisters for encapsulating Sweden's spent nuclear fuel for subsequent safe disposal: electron beam welding and friction stir welding.
Electron beam welding (EBW) for this application has been studied by TWI for around two decades, and prototype equipment has been designed and installed in SKB's canister laboratory in Sweden. More information on this topic is available on this website.
Friction stir welding (FSW), a solid phase joining process invented by TWI in 1991, was first considered for sealing canisters in 1997. Rapid development of the process at TWI showed that it was also capable of producing high integrity welds in 50mm copper.
In May 2005, an SKB press release announced that 'the technique that will be used for sealing the copper canisters is friction stir welding (FSW)'. This decision was based on the results of a series of comparative tests in which FSW was considered to offer the potential of being more reliable and reproducible in the production environment.
Friction stir welding - an alternative method for sealing nuclear waste storage canisters, R. E. Andrews, TWI Ltd, http://www.skb.se
Canister sealing for high level waste encapsulation - TWI staff paper, May 2001
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