Development of the Canister Sealing

After the fuel assemblies have been placed in the canister, the copper canister lid is sealed by welding. The primary welding method is electron beam welding. Another option studied in Sweden is friction stir welding.

Electron Beam Welding

Electron beam welding takes place in a vacuum chamber, where a high-power electron beam is focused on a small area. A piercing hole with a diameter of a few millimetres forms on the object. When the hole proceeds, the material melts and forms a seam, simultaneously also closing the piercing hole.

Electron beam welding has been in use since the 1950s. It is Posiva’s primary option for welding the final disposal canister lid. The method is being tested in Finland at the Patria factory. The sample items currently in use have been manufactured in Finland.

Friction Stir Welding

In friction stir welding, the heat due to friction caused by the rotating tool causes the material to soften. At the same time, the tool is moved forward in such a manner that finished welding is left behind the tool. This is a solid phase welding method as, regardless of its warming up, the material is not molten but starts to resemble chewing gum in its structure.

Friction stir welding, developed in 1991, is the primary welding method used by the Swedish SKB for attaching the copper canister lid to the canister.