Nuclear components built with additive manufacturing require reliable data on how material structure affects safety-critical performance. This project examines laser powder bed fusion (LPBF) fabrication of 316L stainless steel to determine how porosity and microstructure influence fracture toughness, a key metric for nuclear materials qualification. LPBF produces parts layer by layer and is considered a leading candidate for near-term use in atomic applications, yet existing codes and standards lack sufficient toughness data for this process. Research links processing conditions, such as power, scan speed, and post-processing methods like hot isostatic pressing, to the formation of pores, grain size, oxides, and dislocation structures that govern crack resistance. Higher porosity, particularly interconnected pores, creates easier pathways for fracture, while finer grains and oxides formed at faster cooling rates can improve toughness. Part geometry may also introduce variability even under identical processing parameters. Understanding these relationships supports the development of responsible regulatory guidance and expands safe adoption of LPBF-manufactured 316L stainless steel in nuclear systems.