Achieving high-integrity seals in double-layered 316L nuclear waste containers through ultrasonic-frequency pulsed arc deep penetration welding

To address the challenges associated with the safe handling and transfer of spent nuclear fuel that mainly containing Actinide elements, this study proposes a novel container structure and an innovative welding process tailored for radioactive environments. The container features a double-layer 316 L stainless steel design, necessitating deep penetration welding without compromising the inner wall integrity. A specialized non-filler welding process, enhanced with ultrasonic frequency pulsed (UFP) current, was developed to achieve precise control of arc pressure and heat input, enabling full fusion of the outer layer while preserving the structural stability of the inner plate. Experimental results demonstrate that the welding process we designed is capable of realizing the manufacturing of nuclear waste with innovative structural designs. Due to the unique characteristics of the welding process, the welded joint exhibits microstructural and mechanical property inhomogeneity. Microstructural analysis showed columnar and equiaxed grain distributions in the weld zone. The EBSD measurements highlighted varying dislocation densities and grain boundary characteristics across the joint, as a result, the welded joint exhibited uneven hardness. Mechanical testing demonstrated that the welded joints retained over 95 % of the strength and ductility of the base metal, with acceptable tensile properties across thickness positions. The results validate the feasibility of the proposed welding method for fabricating containers capable of leak-free transport of actinide products, significantly enhancing safety and reliability in nuclear fuel cycle operations.