Morell-Pacheco, Andres. The influence of proton irradiation damage on the corrosion of Hastelloy N exposed to FliNaK molten salt

Principal Investigator
First Name:
Andres
Last Name:
Morell-Pacheco
Institution:
Texas A&M University
Title:
PhD candidate
Team Members:
Name: Institution: Expertise: Status:
Lingfeng He Idaho National Laboratory Nuclear Fuels, TEM, radiation effects, Ceramics Faculty
Lin Shao Texas A&M University Radiation Effects, Sensors, ion beam analysis Faculty
Experiment Details:
Experiment Title:
The influence of proton irradiation damage on the corrosion of Hastelloy N exposed to FliNaK molten salt
Describe the work that you are proposing in detail. Please include as many specifics as possible (e.g., dose, dose rate, ion energy, types of ions, beam line x-ray energy, irradiation temperature, analysis temperature, atmosphere, etc.):
Sample preparation: The sample has been cut from alloy stock to desired dimensions and polished/etched to expose grain boundaries. The sample was then sonicated in acetone and rinsed with methanol in preparation for implantation. Sample irradiation: The polished Hastelloy N sample has been irradiated using 2.5 MeV protons at a temperature of 500°C at a high vacuum lower than 1.5e-7 torr. The implantation was accomplished using the National Electrostatics Corp. Pelletron 3MV Accelerator at Texas A&M University. The sample was mounted on an oxidation-resistant Inconel hot stage. The vacuum implantation chamber features a nitrogen cold trap which was refilled hourly throughout the experiment to capture contaminants and improve the operational vacuum pressure. Ions were produced using a titanium hydride cathode in conjunction with a SNICS ion source. The ion beam spot was highly focused, approximately 3 mm × 3 mm. Three different dose spots were implanted onto the long sample, one after the other, in the following order: 1.0 dpa, 0.5 dpa, and 0.25 dpa (local dose). One region of the sample was left unirradiated as a control for comparison during post-irradiation examination (PIE). Corrosion: FLiNaK eutectic salt mixture was prepared at INL with the assistance of the Pyrochemistry and Molten Salt Systems Group. The mixture was prepared from ≥99% metallically pure anhydrous salts and handled entirely in an argon glovebox. The irradiated sample has been immersed in FLiNaK salt within a glassy carbon crucible loaded into a furnace at 700C. This furnace is set up inside of an argon glovebox and the experiment will proceed for 500 hours. The sample will then be cleaned of any residual surface salt using 1M/L aluminum nitrates solution and prepared for post-irradiation analysis. Post irradiation examination: FIB lift-out technique will be used on the two samples in order to produce TEM lamellae. Lamellae will be extracted at 4 different sites on the multi-spot irradiated sample: one at each of the three irradiation damage spots and a forth lamellae from the control spot of the sample. The lamellae will be examined using bright and dark field TEM to characterize defect formation and morphology changes. S/TEM-EDS, EELS and ASTAR will be used in order to characterize elemental segregation/depletion from the alloy as well as grain orientation and strain mapping under the influence of radiation damage.
Technical Abstract
A complete understanding of the evolution of Hastelloy N under adverse conditions needed to confidently operate molten salt reactors (MSRs) for long-term industrial use has yet to be realized. The technical objective of this RTE is to investigate and quantify the effects of radiation-induced point defect and dislocation aggregation on the diffusion and corrosion behavior of Hastelloy N in fluoride molten salt environments. This will be accomplished using a sample irradiated with high-energy protons at Texas A&M University and subsequently exposing the sample to lithium-sodium-potassium fluoride eutectic (FLiNaK) salt at 700°C for 500 hours. After corrosion, changes to sample morphology and elemental distribution, as well as grain orientation characteristics, will be quantified. This will be accomplished using focused ion beam (FIB) for specimen preparation followed by transmission electron microscopy (TEM), scanning transmission electron microscopy-energy dispersive X-ray spectroscopy-electron energy loss spectroscopy (STEM-EDS-EELS) and ASTAR technique available at INL. If successful, an understanding of the quantitative effect of increasing low-dose radiation damage on the morphology of Hastelloy N in corrosive FLiNaK salt environments will be achieved over the next nine months.