Tome Architecture and management of a geological repository - Andra

7 - Spent fuel repository zone• Extrusion processEssentially the extrusion process consists of constructing a hollow ingot then extruding it using ahydraulic press:APréparationdu lingotBExtrusiondu tubeFigure 7.3.3Principles of copper tube construction 50 mm thick by extrusionExtrusion differs from the boring & drawing method in it that requires factory welding at the bottomof the copper envelope.7.3.3.2 Welding processes in an irradiating atmosphereTwo methods have been tested for welding the lid of the copper envelope, which will be carried out inan irradiating atmosphere (as the CU assemblies will be already in position in the cast iron insert):- the friction stir method;- electron beam welding – the same method as used in the manufacture of C waste over-packs(chapter 5.3.3.2).The two methods can be implemented on the tube construction site (in a non irradiating zone) for thecopper canister base weld.• The friction stir welding method (FSW)The friction stir welding process (FSW) was invented in 1991 at the Swedish Welding Institute (TheWelding Institute TWI). It is a thermo-mechanical solid phase process that combines extrusion andforging.A cylindrical, profiled tool is rotated under pressure (friction) along the joint line between the twoelements to be welded. The heat of the friction produced between the wear-resistant tool and the jointfaces of the parts to be welded enables the tool to plunge slowly into the copper (stirring). Bycontrolling the exerted pressure and the rotation speed, the copper does not melt. The tool is thenmoved along the weld line. The transfer of plasticised copper along the tool probe (non-consumable),either side of the two edges submitted to friction, creates a continuous solid phase bond between thetwo parts.A diagram of this process is presented in Figure 7.3.4.Dossier 2005 granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY206/228