Synergistic Irradiation, Corrosion, and Microstructural Evolution in Nuclear Materials: Irradiation-Corrosion of Materials in Molten Salts and Liquid Metal
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Djamel Kaoumi, North Carolina State University; Michael Short, Massachusetts Institute of Technology; Peter Hosemann, University of California, Berkeley; Stephen Raiman, University of Michigan; Raluca Scarlat, University of California, Berkeley; Aaron Kohnert, Los Alamos National Laboratory; Ryan Schoell, Sandia National Laboratory; Philip Edmondson, The University of Manchester; Celine Cabet, Commissariat a l'Energie Atomique

Wednesday 8:30 AM
March 2, 2022
Room: 202A
Location: Anaheim Convention Center

8:30 AM  
On the Use of Corrosion Electrochemistry in Understanding Materials Corrosion in Molten FLiNaK Salts: Ho Lun Chan1; Elena Romanovskaia1; Raluca Scarlat2; Peter Hosemann2; John Scully1; 1University of Virginia; 2University of California Berkeley
    Molten salt nuclear reactor has become a global thrust of clean nuclear energy development through a collaborative effort between academia, national laboratories, and industries. However, our understanding on the corrosion process and subsequent rates of structural materials in these environments is very limited. The combination of in-situ and ex-situ characterization approaches provide new insight of the time dependent processes taking place. In this presentation, an in-situ electrochemical method was developed and employed to study the electrochemical corrosion process of pure metals (Cr, Fe, Ni), Ni-Cr, and Fe-Cr alloys in a molten LiF-NaF-KF eutectic salt mixture at 600C. A systemic set of experiments, including electrochemical impedance spectroscopy, potentiodynamic polarization, mass loss measurement, was performed on these materials over at least 50 hours of exposure. The composition of salts was monitored using cyclic voltammetry with various sensing electrodes during the corrosion of candidate materials.

8:50 AM  
Effect of Ion Irradiated Microstructure on Molten Salt Corrosion of Hastelloy N: Hazel Gardner1; Ryan Schoell2; Jie Qiu3; Fedi Fehri2; Michael Moody1; Peter Hosemann3; Djamel Kaoumi2; David Armstrong1; 1University of Oxford; 2North Carolina State University; 3University of California, Berkeley
    Nickel-based alloy Hastelloy-N was developed decades ago for structural applications in Molten Salt Reactors, where good radiation and corrosion resistance, and high temperature mechanical performance are required. In this study, Hastelloy-N was irradiated with 2 MeV Ni+ ions at 600°C to a peak damage of 10 dpa at ~0.6 microns depth. Both irradiated and non-irradiated regions were then exposed to FLiNaK molten-salt to substantiate the effect of the irradiation-induced microstructure on the molten-salt corrosion behavior of the alloy. The microstructure of the (i) as-received, (ii) irradiated, (iii) corroded, and (iv) irradiated-then-corroded material were characterized respectively using a combination of transmission electron microscopy and atom probe tomography. Ion irradiation alone is observed to cause a ~20% nano-hardness increase, and segregation of Si to dislocation loops and grain boundaries, and the formation of nanoscale Mo/Cr-rich carbides. Analysis of the irradiated and unirradiated alloy after exposure to the molten salt are also presented.

9:10 AM  
Characterizing Commercial Alloys Undergoing Simultaneous Molten Salt Corrosion and Proton Irradiation: Nouf Almousa1; Weiyue Zhou1; Kevin Woller1; Micheal Short1; 1Massachusetts Institute of Technology
    The synergetic effects of irradiation and corrosion of commercial alloys in high-temperature molten fluoride salt are investigated. Using a simultaneous corrosion-irradiation facility [1], a FLiNaK molten salt in a pure nickel corrosion cell is exposed to a proton beam through a 25m foil sample. Cross-section of each foil were specifically prepared using dry ion polishing to preserve salt-filled features and characterized. In order to evaluate the effects of irradiation on corrosion, assessments of the corrosion depth and corrosion acceleration factor have been undertaken. The net corrosion effect is determined by competing, simultaneous processes of acceleration via salt chemistry and deceleration from radiation enhanced diffusion, found to be greatly dependent on alloying elements and associated self-healing. Based on the quantitative corrosion metrics, the impact of the proton beam on the molten salt corrosivity can be summarized in one sentence: Irradiation makes good alloys better and bad alloys worse.

9:30 AM  
One-dimensional Wormhole Morphology Induced by Molten Salt Corrosion in Ni-Cr Alloy: Yang Yang1; Weiyue Zhou2; Sheng Yin3; Sarah Wang4; Qin Yu3; Matthew Olszta5; Daniel Schreiber5; Jim Ciston3; John Scully6; Robert Ritchie3; Mark Asta3; Ju Li2; Michael Short2; Andrew Minor3; 1The Pennsylvania State University; 2Massachusetts Institute of Technology; 3Lawrence Berkeley National Laboratory; 4University of California, Berkeley; 5Pacific Northwest National Laboratory; 6University of Virginia
    The progression of localized corrosion is often accompanied by the evolution of porosities in materials, creating internal mass-flow pathways which facilitate the ingression of the external environment into the interior of the material. Visualizing the morphology of these porosity networks is crucial for the understanding of how materials get penetrated by corrosion. Here, using FIB-SEM 3D reconstruction and TEM tomography techniques, we characterized the unique morphology of porosities in Ni-20Cr after corrosion in FLiNaK molten salt. We discovered that an extremely localized form of corrosion, which we call one-dimensional (1D) wormhole corrosion, is responsible for the fast penetration of salt in Ni-20Cr. Combining advanced electron microscopy and density functional theory simulation, we further deciphered the nano-structural origin of this corrosion morphology and directly imaged the vacancy-supersaturated region as the precursors of wormholes. Our discovery is an important step towards the fundamental understanding of synergistic irradiation and molten-salt corrosion in metals.

9:50 AM Break

10:10 AM  Invited
In-situ Measurement and Analysis of Structural Alloy Corrosion in Liquid Metals: Peter Hosemann1; Jie Qiu1; Franziska Schmied1; John Scully2; Yongqiang Wang3; Blas Uberuaga3; Djamel Kaoumi4; Farida Selim5; Rasheed Auguste1; Junsoo Han2; 1University of California, Berkeley; 2University of Virginia; 3Los Alamos National Laboratory; 4University of North Carolina; 5Bowling Green University
    Heavy liquid metals are candidates for cooling media in fast reactors in the Gen IV nuclear roadmap, with several designs pursuing heavy liquid metal cooled reactors. Furthermore, alloying lithium into heavy metal coolants is also considered for fusion applications. However, a thorough understanding of the structural materials corrosion phenomenon under these combinatorial extreme environments is still missing. This work here presents in-situ and ex-situ examination of Fe-Cr based materials and the protective oxides formed during exposure to liquid metals, addressing fundamental transport mechanisms through passive films in their environment. Positron annihilation spectroscopy and impedance spectroscopy, coupled with conventional microscopy, are used to provide a comprehensive understanding of transport through passive films. This work further highlights in-situ heavy liquid metal corrosion under irradiation performed to date with recent in-situ diagnostics.

10:40 AM  
Investigating Radiation-altered Corrosion in Liquid Lead: Michael Short1; Weiyue Zhou1; Nouf AlMousa1; Kevin Woller1; Djamel Kaoumi2; Ryan Schoell2; Felix Hofmann3; Mark Lapington3; Minyi Zhang3; Michael Moody3; Angus Wilkinson3; 1Massachusetts Institute of Technology; 2North Carolina State University; 3Oxford University
    Radiation has recently been shown to decelerate corrosion in molten salts at reactor-relevant temperatures. Because corrosion in liquid lead proceeds largely via the same mechanisms - selective dissolution - it is hypothesized that this same effect will occur in liquid lead at similar temperatures. In this talk, we will report the first results showing the changes in kinetics and mechanisms of various steels exposed to 650C liquid lead irradiated by protons, in a thin-foil simultaneous corrosion/irradiation facility on an ion accelerator. Dry ion polishing, critical to resolving percolating voids formed during corrosion, is used to fully preserve features for subsequent SEM, TEM, 4D-STEM, and APT analyses to reveal how concurrent irradiation affects corrosion in this potential Generation IV nuclear reactor technology.

11:00 AM  
In situ Monitoring of Corrosion Progression under Irradiation in the Irradiation-Corrosion Experiment (ICE): Franziska Schmidt1; Matthew Chancey2; Yongqiang Wang2; Peter Hosemann1; 1University of California-Berkeley; 2Los Alamos National Laboratory
    Several coolants are considered for next-generation nuclear reactors, including heavy liquid metals (HLMs), such as Pb and Pb-Bi eutectic (LBE). The progression of corrosion in materials subjected to HLM corrosion and irradiation simultaneously is poorly understood and difficult to observe. Data for studies conducted in radiation-corrosion environments can typically only be collected post-experiment, merely providing snapshots of the process. The irradiation-corrosion experiment (ICE) III was designed to expose thin metal foils to LBE and proton irradiation to mimic reactor conditions and provide better insight into coupled irradiation-corrosion effects under these conditions. In addition to results from post-experimental analysis of pure Fe exposed to LBE and 4 MeV protons, we will present new in situ elemental measurements taken during the experiment via proton induced X-ray emission (PIXE) spectroscopy, potentially allowing us to continuously monitor the progression of corrosion.