UK metals R&D group TWI has won an invitation to tender by the French National Radioactive Waste Management Agency (ANDRA).

ANDRA is a government organisation responsible for the long-term management of radioactive waste in France. As part of a strategy to store vitrified high level waste in steel canisters in a facility 500m underground, a tender was issued to develop a new Electron Beam (EB) based welding procedure for the closure of nuclear waste canisters.

A major challenge is not only to remotely weld very thick carbon steel (up to 80mm) in a hot-cell, ie radioactive, environment but also to develop a welding process which can be controlled in such a way that residual stresses in the welds are greatly reduced and the risk of long-term corrosion problems such as stress corrosion cracking is minimised.

The Reduced Pressure Electron Beam (RPEB) technique, developed by TWI and previously applied to the welding of thick section steel for offshore applications, is ideally suited, with minor modifications, to weld the lid to the canister body whilst meeting the stringent quality and safety requirements, TWI said. The benefit of using RPEB is that good material toughness can be retained without significant levels of residual stresses and therefore, the risk of long-term degradation is minimised.