Dev Chidambaram

Molten Na batteries have typical operating temperatures of 300-350°C, requiring complex thermal management and specialized seals. Lowering the operating temperature to less than 150°C would improve the economic feasibility of large-scale molten Na energy storage. The use of Hg metal as a positive electrode enables an operating temperature below 150°C when paired with a Na superionic conductor (NaSICON) solid-state electrolyte. However, poor wetting of NaSICON by liquid Hg increases interfacial resistance and limits achievable current density. In this work, Pt, Cu, and Ag coatings were investigated as a route to improve Hg wetting of NaSICON and reduce the interfacial resistance. The Pt coating lowered the Hg contact angle from 114° (bare NaSICON) to 100°, reduced symmetric-cell impedance nearly seven-fold (18.15 vs. 2.64 Ω cm² at low-frequency), and decreased overpotential nearly four-fold at 0.5 mA cm⁻² (-0.08 V vs. -0.02 V), while forming a stable, coherent film after cycling. Cu and Ag coatings instead worsened the contact angle (135–139°), increased impedance and overpotential relative to bare NaSICON, and were largely stripped from the electrode during testing. Based on these results, a Pt coating on the NaSICON is recommended for improving Hg wetting and lowering interfacial resistance in molten Na-Hg batteries.

Oxygen is a known corrosion accelerator in sodium-cooled fast reactors; however, published studies have primarily used sodium containing no oxygen, saturated oxygen, or one single oxygen concentration and explored the effect of varying temperatures and operating conditions. In this study, we investigate the effect of increasing oxygen concentration on the corrosion behavior of 316L austenitic stainless steel in a static testing environment at 550 °C for 100 h. Surface morphology and chemistry of the samples were then investigated using electron microscopy with focused ion beam milling, energy dispersive spectroscopy, and X-ray diffraction. As oxygen level increased, the continuity and depth of penetration of the established NaCrO ₂ layer were found to increase. Additionally, redeposition of corroded iron in the form of ferrite was observed and seen to increase in size with oxygen concentration. Grazing incidence X-ray diffraction revealed a transition from Cr ₂₃ C ₆ to (Fe, Mo) ₆ C, followed by eventual carbide depletion as oxygen increases. The results of these experiments demonstrate a direct relationship between oxygen concentration and both iron solubility and oxide penetration in liquid sodium systems.

Regeneration and reuse of silver-based sorbents could reduce the economic burden and environmental impact associated with radioiodine capture from used nuclear fuel reprocessing off-gas. Here, three commercially available silver-containing sorbents, IONEX Ag-400 (Ag-exchanged FAU with binder), IONEX NexSorb-99 (Ag-exchanged MOR with binder), and Clariant AC-6120 (Ag-impregnated Al2O3), were evaluated for cyclic iodine loading and regeneration as candidate primary-bed sorbent materials in a dual-bed process. Ag-400 exhibited the highest iodine uptake over three loading cycles, but became increasingly friable as repeated AgI(s) formation during loading and Ag0(s) formation during regeneration collapsed the zeolite framework. NexSorb-99 showed lower but more stable iodine uptake with no detectable degradation of the engineered sorbent during cycling. Although also zeolite-based, the greater structural stability of MOR and the ability of the binder to accommodate repeated phase transformations prevented pellet degradation. AC-6120 exhibited the lowest iodine uptake but maintained physical integrity and the most consistent pore structure during cycling; however, more residual AgI(s) remained after regeneration compared to the zeolite-based materials. These results demonstrate that the viability of sorbents for regeneration and reuse is controlled primarily by support stability and pore accessibility, rather than silver loading alone.

Advanced reactor development presents an opportunity to close the nuclear fuel cycle by integrating proven pyroprocessing and waste disposition principles in parallel with reactor design. In liquid-fueled molten salt reactors (MSRs), fission products accumulate directly in the circulating salt, necessitating periodic processing to maintain reactivity and thermophysical performance. Closing the fuel cycle therefore requires selective separation and recycling of actinides coupled with effective treatment of secondary salt waste streams. This Perspective examines the technical constraints governing fluoride-based MSR fuel recycling and argues that electrochemical selectivity is a tractable design challenge. In particular, the limited separation margins between actinides and lanthanides in fluoride salts require electrochemical strategies that exploit cathode activity reduction, rigorous redox control, and fluoride-compatible processing conditions. We further contend that dehalogenation of fission-product-bearing salt is an enabling step for waste minimization and actinide recycle. By framing these coupled challenges within an integrated, fluoride-compatible pyroprocessing strategy, this work identifies key design levers and research priorities required to enable continuous actinide recycling and sustainable MSR deployment.

Generation IV reactors aim for more efficient, cheaper, safer nuclear power with less waste generation. Sodium-cooled fast reactors (SFRs) are expected to be among the first GenIV designs to operate. SFR structural and cladding materials must withstand high‐temperature liquid sodium, where degradation is driven by selective dissolution and impurity‐mediated reactions rather than electrochemistry. This review focuses on corrosion and mass transfer in sodium, highlighting the coupled role of temperature gradients, flow velocity, and impurities (notably oxygen and carbon) in driving elemental leaching and redistribution, carburization/decarburization, and formation of stable ternary oxides such as Na–Cr–O compounds. Corrosion behavior is then assessed for major candidate classes: austenitic stainless steels as a performance baseline; ferritic–martensitic steels and the role of carbon activity and chromium content; ODS steels and chemistry-dependent oxide development; nickel-based alloys with comparatively high sodium solubility; and SiC/SiC composites with impurity-sensitive intergranular attack. A database of recent experiments (temperature, impurity level, flow, exposure time) is used to map existing data and expose gaps for advanced cladding deployment. Key gaps are the limited parametric studies spanning oxygen/carbon activity, velocity, and irradiation damage, and the lack of long-duration datasets and validated mechanistic models for SFR deployment.

The electrochemical reduction of iron oxides in highly alkaline media (pH ≥14) offers a promising low-temperature, low-carbon pathway for sustainable iron production. However, the harsh conditions limit the use of conventional reference electrodes (RE), while accurate interpretation of electrochemical data depends critically on RE’s reliability. Here, platinum wire is evaluated as a quasi-reference electrode (QRE) during the electrochemical reduction of hematite (Fe2O3) in 10M NaOH at 75°C. Cyclic and linear sweep voltammetry reveal a Fe2O3 reduction peak near -1.1V vs Pt QRE, followed by hydrogen evolution around -1.25V. Chrono-potentiometry demonstrates sustained iron deposition for up to 10h with Faradaic efficiencies of 50–60%, confirming the feasibility of alkaline electrochemical ironmaking. X-ray diffraction and SEM-EDX analysis confirm phase-pure metallic α-Fe formation with a dendritic morphology. The Pt QRE performed reliably under low current operations but showed significant drift at higher currents as hydrogen evolution drives equilibration of the Pt surface with the H2/H2O couple, resulting pseudo-reversible hydrogen electrode behavior. Auxiliary channel measurements of WE-RE, WE-CE, and CE-RE couples confirmed the RE as the source for potential drifting. Complementary measurements using a Hg/HgO RE validated with Pt QRE results within a 70-100 mV shift at low currents while delineating their limitations clearly.

This review focuses on the critical issue of water and related impurities in halide salts, particularly relevant in the context of high-temperature energy storage and conversion systems like molten salt nuclear reactors, concentrating solar power, pyroprocessing of nuclear fuel, and thermal energy storage. The corrosive nature of molten halide salts is exacerbated by hydroxides, oxides, oxyhalides, and hydrogen halide acids that form when halide salts are heated and fused with water present. Precise quantification of water and related species is vital for advancing fundamental research necessary for the development of these systems and for safe and economical operation of commercial systems in the future. The literature regarding (i) the structure and speciation of water and water-related impurities, (ii) drying and purification methods to reduce water in halide salts, and (iii) methods for detecting and quantifying water and related reaction products have been reviewed and compiled here. This review highlights the complex behavior of water in halide salts and the challenges involved in rigorous quantification. Pathways towards better understanding fundamental molten salt chemistry and developing quantification methods with improved accuracy are also discussed. Development of complementary analytical techniques will not only be crucial for high-fidelity molten salt experimental research but also essential for developing and optimizing the safety, performance, and longevity of molten halide salt-based energy systems.

Increasing energy demand and a desire for energy security have spurred interest in next-generation high-temperature energy technologies. These technologies include new nuclear reactors and reprocessing of used fuel, concentrated solar power, high-temperature energy storage, and grid-scale batteries. All of these, except grid-scale batteries and reprocessing of used nuclear fuel, require the use of a heat engine operating with the Rankine (steam) or Brayton (supercritical CO2) cycles to convert thermal energy to electrical energy. Next-generation energy technologies use high-temperature heat transfer fluids. Due to their high temperature stability, low vapor pressures, and high heat capacities, both halide salts and molten metals are attractive heat transfer materials. A major barrier to the implementation of these fluids is their corrosivity to structural materials in their application. This article discusses the corrosion mechanisms in molten salts and metals in their use in energy applications.

Renewable energy systems will need large-scale energy storage to ensure reliability and provide power when and where it is needed. Even though lithium-ion batteries are increasingly used for large-scale storage, their costs and competition in terms of materials needed for electric vehicles are driving the need for alternative batteries for stationary energy storage systems. Molten sodium-ion batteries that operate at intermediate temperatures, approximately 150 °C or less, offer an abundant and cost-effective solution to our energy storage issues. This review paper highlights the materials, enhancements, and performance of molten Na–ion batteries that operate at temperatures at or below 150 °C for use in energy storage systems as well as an outlook on future improvements for this energy storage system.