Fundamental study of Nd:YAG laser beam welding for lower end plug using HT9 alloy cladding tube

Abstract

Various welding processes are now available for the end plug closure of a nuclear fuel element such as gas tungsten arc welding (GTAW), magnetic resistance welding, and Nd:YAG laser beam welding (LBW). Even though the resistance and GTAW processes are widely used for manufacturing commercial fuel elements, they cannot be recommended for the precise end plug welding of fuel elements owing to the complexity of a tungsten electrode alignment, wide heat-affected-zone (HAZ) and concave shapes and large heat input for thin cladding tubes. Therefore, Nd:YAG LBW using optical fiber transmission was selected for lower end plug welding using an HT9 alloy cladding tube. To establish the LBW process, and satisfy weld quality requirements, preliminary experiments for optimizing the welding conditions which used test specimens with a lower end plug of the cladding tube were performed. This paper describes the experimental results of the LB welded specimens using lower end plugs, along with the measurements of weld profiles and metallographic examinations. Furthermore, the effect of undercut depth and penetration depth after lower end plug welding was also investigated by changing the laser welding parameters and various dimensional configurations.Various welding processes are now available for the end plug closure of a nuclear fuel element such as gas tungsten arc welding (GTAW), magnetic resistance welding, and Nd:YAG laser beam welding (LBW). Even though the resistance and GTAW processes are widely used for manufacturing commercial fuel elements, they cannot be recommended for the precise end plug welding of fuel elements owing to the complexity of a tungsten electrode alignment, wide heat-affected-zone (HAZ) and concave shapes and large heat input for thin cladding tubes. Therefore, Nd:YAG LBW using optical fiber transmission was selected for lower end plug welding using an HT9 alloy cladding tube. To establish the LBW process, and satisfy weld quality requirements, preliminary experiments for optimizing the welding conditions which used test specimens with a lower end plug of the cladding tube were performed. This paper describes the experimental results of the LB welded specimens using lower end plugs, along with the measurements of weld prof...