Molten salt reactors (MSRs) are gaining attention due to their potential for safe, carbon-free nuclear energy with reduced waste. However, licensing these reactors is hindered by limited experimental data on fueled salts, both pre- and post-irradiation. The novel Molten-salt Research Temperature-controlled Irradiation (MRTI) vehicle was designed to address knowledge gaps in irradiating enriched-uranium-bearing salts. The MRTI experiment irradiated 13 cm3 of UCl3-NaCl (93 % U-235) salt in the Neutron Radiography (NRAD) Reactor, achieving a burnup of 0.196 GWd/MTU over 390 h. Despite a heater failure, the thermocouple data suggested fission heat kept the salt molten. The MRTI assembly was remotely disassembled for nondestructive post-irradiation examination (PIE), which included precision gamma-ray scanning (PGS) and neutron radiography. Radiograph images showed the location of the salt and the solidification pattern. PGS results provided an early indication that activated materials of construction did not increase in relative intensity in the region of the capsule where the salt was in contact with the material of construction. Additionally, PGS data showed the presence of several gamma emitting fission products, such as Nb-95, Zr-95, Ru-103, Ce-141, and La-140, where Ru-103 had the highest counts at the bottom of the capsule. Computational fluid dynamics modeling supported observations of salt solidification patterns and proved to be a valuable tool to inform PIE activities. The MRTI experiment has thus far provided critical data and lessons learned for fuel salt PIE activities, essential for advancing the technical readiness of MSRs.

Corrosion of structural materials is a key engineering challenge for the development of molten salt reactors (MSRs). Metal ion impurities in the salt, which are inevitable due to their natural evolution in a reactor (e.g. fission products, corrosion products, etc.) can significantly impact the corrosion performance of structural materials. In this work, we investigated the effects of one fission product, Eu in its 3 + oxidation state, on the corrosion behaviors of pure Ni metal and Ni-20Cr model alloy in molten LiCl-KCl eutectic using in situ optical spectroscopy, post-corrosion inductively coupled plasma mass spectrometry (ICP-MS) and electron microscopy-based techniques. The EuCl 3 -containing salt was found to be extremely corrosive to both Ni and Ni-20Cr. Detailed microstructural characterization revealed that pure Ni primarily exhibited planar corrosion fronts with occasional shallow intergranular attacks, while Ni-20Cr alloy showed severe localized intergranular attacks with selective Cr leaching and salt penetration near grain boundaries. Additionally, this study uncovered the unique intragranular crystallographic attack of Ni-20Cr under exposure to EuCl 3 -containing salt. Overall, these findings are crucial for understanding how oxidizing salt impurities such as EuCl 3 affect corrosion reactions and diffusion kinetics at the salt-material interface, thereby influencing corrosion microstructure evolution pathways.

Liquid fuel salts are being proposed and explored as fuels and coolants for molten salt reactors, where alloy corrosion by salt presents a significant challenge. This study investigated the corrosion behavior of Inconel 625 alloy exposed to UCl₃–NaCl (33–67 mol%, 93% U-235) fuel salt under neutron irradiation conditions. The fuel salt was contained within an Inconel 625 capsule in a Molten-salt Research Temperature-controlled Irradiation (MRTI) vehicle and irradiated for approximately 390 hours in the Neutron Radiography reactor, achieving a burnup of 0.196 GWD/MTU. Heater failure during irradiation created a temperature gradient (583–804 K) in salt, resulting in salt stratification with higher NaCl concentration in the upper solidified region and elevated fission product concentrations at the bottom. Post-irradiation examination of the Inconel-625 surface and cross-sectional analyses showed chromium and molybdenum depletion within ∼5 μm of the capsule surface, accompanied by iron and nickel enrichment, indicating reduction-oxidation reactions between dissolved corrosion products and alloy constituents. Assuming a 5 μm corrosion layer and 390 hours of irradiation, the calculated corrosion rate at the lower temperature part is 0.11 mm/year, a relatively low corrosion rate under the conditions of this study. Uranium metal deposits were identified on the capsule wall, attributed to the disproportionation of U3+. Noble metal fission products (Nb, Mo, Rh, Ru, Sb, and Tc) exhibited higher concentrations in the bottom salt segment, suggesting gravitational settling, while lanthanide fission products remained uniformly distributed. These findings provide critical insights into fuel salt-structural material interactions and fuel performance under irradiation conditions.

Stainless steel 316 L exposed to LiCl-Li2O molten salt containing Li metal for 500 and 1000 h experiences deep intergranular attack and bulk void formation. This degradation is due to a synergistic corrosion mechanism, different than other forms of molten salt corrosion, where Cr and Mn oxides and carbides form along grain boundaries and are dissolved by Li metal. Synchrotron transmission X-ray microscopy 3D imaging is used to show corrosion morphology and Cr enrichment and depletion in a novel format that has not previously been used for bulk corrosion samples.

Molten salt reactors (MSRs) have garnered increasing attention recently with several demonstration efforts on the way. A key challenge to the licensing basis for these reactors is the lack of experimental data on fueled salts. This is expected to be crucial to the safety evaluation and licensing basis of reactors of this type deployed in the future. While capability for irradiating molten salts has been reestablished in the recent decade, no enriched fuel irradiation capability has been developed and tested as of yet. A new experiment vehicle under development at Idaho National Laboratory (INL) is presented here. The Molten-salt Research Temperature-controlled Irradiation (MRTI) experiment was developed to host enriched uranium bearing salt samples to be irradiated at a test reactor within the lab complex. One of the key scientific objectives is to provide irradiated salt samples for postirradiation examination (PIE) to study the impact of fission product generation and neutron/gamma radioactivity on the salt solution and salt-facing wall material. This paper provides a detailed overview of the mechanical design of the experiment, followed by an overview of the fabrication and assembly of an initial prototype vehicle (with non-fuel-bearing salt). A summary of the key analyses conducted as a part of the performance and safety evaluation is then provided. Lastly, an overview of the test conducted in prototypic out-of-pile (non-neutron) environment are shown. These evaluations provide the foundation for a planned irradiation of an enriched uranium-bearing chloride salt sample in the near term. The upcoming irradiation will contain 13 cm3 of UCl3-NaCl salt (93% enrichment) generating around 20 W/cm3 of fission energy during irradiation and a temperature range that can be contained between bounds of 525-900 degrees C.

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In this study, the structure and coordination environment of two 3d transition elements (Ni and Cr) is investigated in a molten chloride salt system. Electronic absorption spectroscopy was employed to elucidate their coordination environment in 3LiCl-2KCl eutectic salt, as a function of temperature. Density functional theory (DFT) modeling was used to determine the coordination environment of the transition metal species in the eutectic composition as well as the optical spectra computationally. The Ni2+and Cr3+ exist in a tetrahedral and octahedral coordination environment, respectively, in eutectic salt. The spectra thus obtained were compared with the experimental data; a reasonable qualitative agreement was obtained between experimental and computational Ni2+ and Cr3+spectra, and the coordination of both elements in the eutectic composition were in excellent agreement with the experimentally determined results. Computational results were also obtained for two 4d elements, Mo3+ and Nb3+, with both quantum molecular dynamics (QMD) and hybrid functional optical spectra indicating octahedral coordination.

Irradiation testing of fuel-bearing molten salts is critical for supporting the development and demonstration of molten salt reactors (MSRs). These experiments can inform several important reactor design and safety parameters, including source term modeling, the evolution of thermophysical properties with burnup, and the degradation of structural materials under reactor-relevant conditions. Idaho National Laboratory is designing an instrumented and heated high-temperature molten-salt-fueled irradiation capsule to study the behavior of the fuel salt during in-pile irradiation. This paper details the neutronics, thermal, and mechanical analyses performed to date. Parametric studies were performed to assess a range of materials, different experiment dimensions, two in-reactor positions, and the fuel enrichment used. The principal recommendations are to select a peripheral reactor position in order to alleviate neutronic constraints, a thin salt annulus to achieve thermal design objectives, and high-temperature alloys that provide additional safety margins.

The defining characteristic of molten salt reactors (MSRs) is the use of molten salts as the primary heat transfer medium, operating at or near atmospheric pressure, and at temperatures above 500 °C. The fuel may be dissolved into the circulating salt, allowing a possibility for online salt processing, or the fuel may be in a solid form immersed in the coolant salt. Fluoride salt systems have received the most attention and have been used in two demonstration reactors. Nevertheless, chloride salt systems are also proposed for development and deployment. Molten salt properties, their purification, and corrosion control in molten salt systems are important aspects of molten salts for reactor application.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to "Radiation-Assisted Formation of Metal Nanoparticles in Molten Salts"Elaine T. DiasElaine T. DiasMore by Elaine T. Dias, Simerjeet K. Gill*Simerjeet K. Gill*Email: [email protected]More by Simerjeet K. Gillhttp://orcid.org/0000-0003-4955-4509, Yang LiuYang LiuMore by Yang Liu, Phillip HalstenbergPhillip HalstenbergMore by Phillip Halstenberghttp://orcid.org/0000-0002-6030-4503, Sheng DaiSheng DaiMore by Sheng Daihttp://orcid.org/0000-0002-8046-3931, Jiahao HuangJiahao HuangMore by Jiahao Huang, Julia MauszJulia MauszMore by Julia Mausz, Ruchi GakharRuchi GakharMore by Ruchi Gakhar, William C. PhillipsWilliam C. PhillipsMore by William C. Phillips, Shannon MahurinShannon MahurinMore by Shannon Mahurinhttp://orcid.org/0000-0003-3792-1631, Simon M. PimblottSimon M. PimblottMore by Simon M. Pimblotthttp://orcid.org/0000-0001-9169-3030, James F. WishartJames F. WishartMore by James F. Wisharthttp://orcid.org/0000-0002-0488-7636, and Anatoly I. Frenkel*Anatoly I. Frenkel*Email: [email protected]More by Anatoly I. Frenkelhttp://orcid.org/0000-0002-5451-1207Cite this: J. Phys. Chem. Lett. 2021, 12, 7, 1777Publication Date (Web):February 12, 2021Publication History Published online12 February 2021Published inissue 25 February 2021https://pubs.acs.org/doi/10.1021/acs.jpclett.1c00451https://doi.org/10.1021/acs.jpclett.1c00451correctionACS PublicationsCopyright © 2021 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views781Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (636 KB) Get e-Alertsclose Get e-Alerts

To examine ion solvation, exchange, and speciation for minority components in molten salts (MS) typically found as corrosion products, we propose a multimodal approach combining extended X-ray absorption fine structure (EXAFS) spectroscopy, optical spectroscopy, ab initio molecular dynamics (AIMD) simulations, and rate theory of ion exchange. Going beyond conventional EXAFS analysis, our method can accurately quantify populations of different coordination states of ions with highly disordered coordination environments via linear combination fitting of the EXAFS spectra of these coordination states computed from AIMD to the experimental EXAFS spectrum. In a case study of dilute Ni(II) dissolved in the ZnCl2+KCl melts, our method reveals heterogeneous distributions of coordination states of Ni(II) that are sensitive to variations in temperature and melt composition. These results are fully explained by the difference in the chloride exchange dynamics at varied temperatures and melt compositions. This insight will enable a better understanding and control of ion solubility and transport in MS.

Pyrochemical reprocessing (pyroprocessing) of used nuclear fuel (UNF) is a promising pathway towards closing the nuclear fuel cycle by recycling actinides into new fuel and providing the means to generate durable wasteforms for portions of the UNF that are not able to be recycled. One of the most significant challenges in the advancement of this technology is developing a more complete understanding of the chemistry of the electrolyte molten salts used in the electrorefining process, where fission products, transuranic elements and fuel elements are anodically dissolved into a LiCl-KCl electrolyte, forming a chemically complex mixture. To enhance our understanding of the chemistry of the mixture of molten salt electrolyte and UNF we are studying the structure and speciation of lanthanide and actinide elements dissolved in LiCl-KCl using Raman and ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy. These techniques are starting to provide information on the coordination, symmetry, and electronic structure of the dissolved species, which will result in a more complete understanding of the chemistry of these solutions. Results of a Raman spectroscopy study of mixtures of NdCl3, SmCl3, CeCl3, and EuCl3 with LiCl-KCl and LiCl-KCl-UCl3 and the development of a system to conduct Raman and UV-Vis-NIR spectroscopy and spectroelectrochemistry will be presented. Acknowledgements: This work was performed under the auspices of the Department of Energy (DOE) under contracts DE-NE0008889, and the US Nuclear Regulatory Commission (NRC) under contracts NRC-HQ-13-G-38-0027 and 31310018M0032. Dr. Kenny Osborne and Ms. Nancy Hebron-Isreal serve as the program managers for the DOE and NRC awards, respectively. For support of furnace design and fabrication work at INL, RG and WCP acknowledge the Laboratory Directed Research & Development (LDRD) Program under DOE Idaho Operations Office Contract DE-AC07-05ID14517 and a subcontract under LDRD (INL) to University of Nevada, Reno via award number 204471 (UNR award AWD-01-00001719); this design served as starting iteration for this work. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1447692. One of the authors, JM, acknowledges the Graduate Research Fellowship from the US National Science Foundation.

Understanding the factors that control solubility and speciation of metal ions in molten salts is key for their successful use in molten salt reactors and electrorefining. Here, we employ X-ray and optical absorption spectroscopies and molecular dynamics simulations to investigate the coordination environment of Ni(II) in molten ZnCl2, where it is poorly soluble, and contrast it with highly soluble Co(II) over a wide temperature range. In solid NiCl2, the Ni ion is octahedrally coordinated, whereas the ZnCl2 host matrix favors tetrahedral coordination. Our experimental and computational results show that the coordination environment of Ni(II) in ZnCl2 is disordered among tetra-and pentacoordinate states. In contrast, the local structure of dissolved Co(II) is tetrahedral and commensurate with the ZnCl2 host's structure. The heterogeneity and concomitant large bond length disorder in the Ni case constitute a plausible explanation for its lower solubility in molten ZnCl2.