316L Stainless Steel Wire Arc Additive Manufacturing and Characterization for Potential SNF Canister Production

Abstract

In this paper, 316L stainless steel (316L SS) straight walls, curved walls, and vessels were printed by wire arc additive manufacturing (WAAM) using the 316L SS welding wire to demonstrate the feasibility of spent nuclear fuel (SNF) canister fabrication using this advanced manufacturing technique. Helium leak tests with a leak-tight criteria of 1 × 10-7 ref-cc/s were performed on the printed vessels with various wall thicknesses. Testing pressures ranged from 0.345 MPa (50 psi) to 1.724 MPa (250 psi). Printed wall microstructures were characterized using optical microscopy (OM) and scanning electron microscopy (SEM). Tensile specimens were machined from the printed walls along length, height, and thickness directions and were tested at different temperature conditions, including room temperature and at 80, 150 and 250°C. Results show that all five WAAM-printed canisters with different thickness passed the American National Standards Institute (ANSI) N14.5 helium leak tight criteria for radioactive materials containers. Dispersed micrometer-level size inclusions/voids were observed at the printed wall cross sections, dendritic microstructures were found with grain size variation through the welding torch shifting direction, and very small amounts of δ-ferrite and σ-phase were also observed in those cross sections. The printed walls were ductile, all tensile specimens broke with large plastic deformation/elongation and without brittle failure, and the yield and tensile strengths of the printed specimens at room temperature and 80°C were greater than the minimum values for 316L SS pressure vessels and for general applications at room temperature as required by the ASTM standard, respectively.