Additive manufacturing tools are capable of programmatically applying corrosion-resistant stainless steel claddings to carbon steel components (e.g., reactor pressure vessels, piping) used in nuclear reactors. Such claddings have lower dilution, a smaller heat-affected zone, and more desirable microstructures compared to arc welded claddings. This research examines the effects of proton irradiation on the corrosion performance of 309L stainless steel claddings fabricated by a laser-wire directed energy deposition additive manufacturing method. Samples are irradiated with 1.5 MeV protons to 0.5 and 1.0 displacements per atom (dpa) to simulate lifetime radiation damage of reactor pressure vessel claddings and are compared to the unirradiated case. The claddings are electrochemically tested in an aerated boric acid-containing electrolyte to simulate refueling conditions in light water reactors. All claddings are exceedingly corrosion-resistant, yet the higher radiation doses show slightly decreased performance, likely due to radiation-induced segregation effects.
The reactor pressure vessel (RPV) is one of the most vital components to nuclear reactor operation. RPVs are made from forged low alloy steel and then typically clad on the inside with austenitic stainless steel (SS) to protect from corrosion.1,2 Traditionally, RPV claddings are applied with gas tungsten arc welding or submerged arc welding, though these arc welding processes require the use of a high heat input to achieve this dissimilar metal bond. The high heat input leads to excess residual stress, a large heat-affected zone, and deleterious phase formation, including sigma phase, sulfides, carbides, and martensite at the dissimilar metal boundary.2-7 Such undesirable phases can affect mechanical integrity and corrosion behavior, particularly when exposed to elevated temperatures and radiation damage.
Advanced laser and electron beam cladding and additive manufacturing processes show promise for enhancing material performance as compared to arc welded claddings.8-13 The considerably reduced heat input in high energy beam cladding processes creates more desirable microstructures, which can potentially extend RPV cladding lifetimes. However, their corrosion performance in light water reactor environments is currently unknown. Additionally, radiation damage accumulated over the reactor lifetime can potentially change the cladding microstructure, impacting its corrosion performance.14-17 For austenitic SS welding alloys, radiation-induced segregation is known to cause Cr migration away from grain boundaries and interfaces, which can degrade corrosion resistance.16,17
