Optimum rotational speed in FSW of copper canisters for nuclear waste

Abstract

The high-level radioactive waste will be encapsulated in copper canisters and stored in a deep repository. High power electron beam welding was the only viable method available at that time for welding thick section copper. In recent years, friction stir welding has been replaced with electron beam welding because of the promotion in mechanical properties and corrosion resistance of copper canisters. FSW is used in solid state, therefore residual stresses produced in the weld is less than that of other welding processes which are performed in the molten state. To obtain optimum rotational speed, FSW was carried out in copper plates with a thickness of 4 mm at a constant speed of 25 mm/minute. The temperature distribution indicated a severe increasing of temperature upon increasing the rotational speed from 900 to 1200 rpm. Also, analysis of the metallographic images showed that the grain size in the nugget zone increases by increasing the rotational speed. Vickers hardness test was conducted on the welded samples and the maximum hardness was obtained at a rotational speed of 900 rpm. Results of tensile tests and their comparison with those of the base metal showed that the maximum strength and minimum elongation are achieved at the same rotational speed.

Keywords

• nuclear waste
• fsw
• mechanical properties
• copper