Jeff King and team explore radiation’s impact on additively manufactured stainless steel and Inconel
The use of additive manufacturing (AM) for mission-critical applications is often limited due to a lack of characterization and property data, which is necessary to meet quality assurance requirements. The nuclear industry is no exception. Data is needed on the performance of AM parts during irradiation in a nuclear reactor to ensure that they can survive and function as intended in challenging nuclear energy environments.
Dr. Jeffrey King and his team at Colorado School of Mines are collecting irradiation performance data for stainless steel (SS) and Inconel samples from billets produced using different AM techniques, including laser powder bed fusion, laser free-form fabrication, and electron beam wire feed. Mines is conducting pre-irradiation thermomechanical testing (tensile strength, yield strength, elastic modulus, ductility, thermal conductivity and thermal diffusivity) and microstructural characterization of the unirradiated specimens. Mines is uniquely positioned to research this area with its strong materials background and interdisciplinary nuclear program as well as with the work of the Nuclear Science and Engineering Center (NuSEC) and ADAPT.
“We’re not the first to do this, but we’re close,” said King. Bombarding metals with neutrons causes physical changes, typically making metals harder but more brittle, or more likely to break suddenly. King’s research examines how additively manufactured parts might perform in a reactor environment compared to conventional parts. “We hope to show AM materials where strength goes up or stays the same and ductility does not go down,” noted King.
AM could benefit the nuclear industry in several ways. Additive processes could be used to create novel geometries for components that improve reactor performance, such as filters or fuel elements. Additionally, given that most nuclear plants are decades old, there are critical parts, such as valves, that are no longer made and that are expensive to replace. This issue is also common in the military, as investigated in ADAPT’s hinge redesign program with the U.S. Army’s CCDC Ground Vehicle Systems Center (previously named TARDEC). AM could enable single replacements of reactor parts to be made at reasonable cost with short turnaround time.
The Advanced Test Reactor (ATR) at Idaho National Laboratory irradiated a set of specimens produced by Dr. King’s group. The ATR is the highest-power research and testing reactor in the United States. It has a fraction of the power of most commercial nuclear plants, but 10 times their neutron flux. The effects of that flux on AM metal parts are what King and his colleagues hope to observe.
Thermomechanical testing and microstructural characterization of the irradiated specimens will begin soon at the Low Activation Materials Design and Analysis (LAMDA) facility at Oak Ridge National Laboratory and the Nuclear Science User Facilities (NSUF) at Idaho National Laboratory.
A comparison of the physical properties and microstructure of the irradiated specimens to those of the as-fabricated specimens will provide insight into the viability of AM parts for nuclear reactor applications. It will also identify key areas of concern for further technology development efforts and provide data for future computational model development.
The NSUF continues to provide funding and facility support for this project. For more on Jeffrey King, visit https://metallurgy.mines.edu/project/king-jeffrey/.