Effect of Water Chemistry on Crack Growth Rates in Neutron Irradiated Additively Manufactured 316L and 718

Abstract

There are significant opportunities within existing light water reactors (LWR) and future small modular reactor designs using additively manufactured components due to the increased capability of additive manufacturing (AM) techniques to facilitate the manufacturing of complex components while achieving potentially equivalent properties to wrought materials. Additively manufactured 316L and Alloy 718 were produced by Direct Metal Laser Melting (DMLM) fabrication. 0.4 inch thick compact tension specimens from each material were used to study crack growth rates for two sample fluences in both normal water chemistry (NWC) at 2.5 ppm O₂ and hydrogen water chemistry (HWC) at ~80 ppb H₂ after being irradiated to ~1 x 10²¹ n/cm², E > 1MeV in the Advanced Test Reactor at Idaho National Laboratory. Crack growth rate (CGR) testing was conducted at a temperature of 288 °C. A decrease in CGR was observed for both alloys when transitioning from NWC to HWC, which was the expected behavior. Severe deviation from the initial crack plane was observed for both AM 316L and 718, which may be due to the grain structure developed using this manufacturing process which encouraged crack propagation in a direction away from the crack plane. Detailed results of CGR response to varying environmental electrochemical potential (ECP) and water purity will be presented in the context of crack growth mitigation in different water chemistries and the change in material behavior relative to traditionally manufactured material.