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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Impact of Actinide Complexation on Ligand Radiolysis

Although the actinides boast many unique physical and chemical properties, their inherent susceptibility to radioactive decay are what make them truly interesting elements to study. The absorption of ionizing radiation from actinide decay leads to the formation of a variety of transient and steady-state radicals, ions, and molecular radiolysis products that can lead to significant changes in the surrounding environment, and ultimately dictate steady-state actinide redox distributions and the longevity of molecules designed for actinide complexation. Radiolysis of the latter leads to complexant destruction and the concomitant formation of degradation products that can complicate actinide studies and processes. However, the radiation chemistry of most actinide complexants have been studied in the absence of the actinides they were designed to complex, which can lead to inaccurate conclusions on longevity and degradation product distributions, as metal ion complexation has been historically shown to influence a ligand’s radiolytic behavior. Consequently, bridging this knowledge gap is important for actinide science. Here, I will discuss the impact of actinide complexation on the steady-state and time-resolved radiation-induced reactivity of a variety of complexants, including, tributyl phosphate (TBP) and N,N,N',N'-tetraoctyl diglycolamide (TODGA) .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

The Role of Pulse Radiolysis in Advanced Nuclear Fuel Cycles

The effects of ionizing radiation are ubiquitous throughout all aspects of a nuclear fuel cycle. The complexity and intensity of these effects are greatest during reactor operations and in the management of used nuclear fuel and waste. Radiation-induced processes typically promote the chemical transformation of molecules and materials with the formation of potentially detrimental degradation products and corresponding changes in physical and chemical properties, which ultimately impact the effectiveness and longevity of nuclear technologies. Consequently, a molecular-level understanding of radiation effects over multiple time, distance, and material domains is essential for the innovation and deployment of next generation nuclear technologies. Attaining this knowledge necessitates a firm grasp of radiation-induced reaction kinetics, for which pulsed electron radiolysis is the methodology of choice. Presented here are several recent studies from our group that demonstrate the critical role of pulsed electron radiolysis techniques in the advancement of our understanding of radiation-induced chemistry under advanced nuclear fuel cycle conditions. Research topics include late actinide redox chemistry, radiation robustness of used nuclear fuel reprocessing complexants, and the behavior of metal cations in high temperature molten salt media.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2026

Modeling Radiolysis and Chemical Reactions during Dry Storage of Aluminum-clad Spent Nuclear Fuel

After aluminum-clad spent nuclear fuel (ASNF) is removed from the reactor, it is initially stored in spent fuel pools, which are specially designed water-filled basins that provide temporary cooling to reduce the temperature of the fuel assemblies and provide radiation shielding. ASNF continues to generate heat due to the radioactive decay of elements within the fuel, which persists for many years post-shutdown as the residual radioactive products decay into more stable elements. During the wet storage period, an oxyhydroxide layer composed of boehmite/bayerite forms on the surfaces of the aluminum cladding from exposure to water in the pools. Road-ready packaging for long-term disposition of the ASNF involves dry storage in helium backfilled DOE standard canisters (DSCs). When the ASNF is removed from water storage and dried, most of the water is removed, but some physisorbed and chemisorbed water remains in the oxyhydroxide layers. This residual water can produce hydrogen when exposed to radiation from the ASNF during dry storage. Predicting hydrogen accumulation over time in the DSCs is critical for long-term storage considerations. Previous modeling efforts have developed coupled computational fluid dynamics (CFD)-chemical models to simulate temperature, pressure, and gas phase concentrations within the DSCs. These models use the thermal field predicted by CFD as input to a radiolysis model for the gas phase and the surface oxyhydroxide layer chemistry. Given the long storage period of the DSCs and the impracticality of long-term experiments, a simulation-based approach is necessary to assess chemical evolution within the canisters. This study advances the development of a modeling framework designed to simulate the chemical evolution of spent fuel canisters. Both thermal and radiation-driven reactions are considered, with radiation kinetics quantified using G-values. Sensitivity analysis identifies key parameters influencing species composition. Reaction pathway diagrams offer insight into dominant species formation routes, enabling more effective comparisons between model predictions and experimental observations, particularly regarding the production of hydrogen. Results show that the model predicts significant hydrogen gas production with minimal oxygen generation, primarily due to hydrogen formation via boehmite pathways. These findings underscore the importance of accurately characterizing surface-bound species and radiolysis kinetics. A deeper understanding of these mechanisms is critical for evaluating the long-term safety of nuclear waste storage.

12 - MGMT OF RADIOACTIVE AND NON-RADIOACTIVE WASTE↗
DOE OSTI2026

Pulse radiolysis and transient absorption spectra of aqueous solutions of sodium sulfamate

Chemical kinetics for the reactions of sulfamate ions (NH 2 SO 3 − ) with the primary products of water and nitric acid radiolysis were measured in aqueous solutions at ambient temperature. Using time-resolved electron pulse radiolysis techniques with a custom multichannel detection system, we examined the reactivity of NH 2 SO 3 − with the hydroxyl radical ( • OH), hydrogen atom (H • ), and nitrate radical (NO 3 • ). The sulfamate ion was found to react with • OH and H • with second-order rate coefficients of k • OH = (5.60 ± 0.04) × 10 6 M −1 s −1 and k H • = (7.96 ± 0.10) × 10 6 M −1 s −1 , respectively, and with NO 3 • with a rate coefficient of k NO 3 • = (1.67 ± 0.06) × 10 7 M −1 s −1 . The reactions of NH 2 SO 3 − with • OH and H • resulted in the formation of two transient radical species, one with maximum absorbance at 300 nm and a second with maxima at both 300 nm and 600 nm. These spectra are tentatively assigned to • NH 2 SO 3 and • NHSO 3 − , respectively. By measuring the absorbance of these radicals as a function of pH, the radical pK a was determined to be 9.5 ± 0.1. Overall, this work has implications for the longevity and performance of ferrous sulfamate, Fe(NH 2 SO 3 ) 2 , as a plutonium reductant in the reprocessing of used nuclear fuel.

Conrad, Jacy K. [Idaho National Laboratory (INL), ↗
DOE OSTI2021

The Application of Pulse Radiolysis to the Study of Ni(I) Intermediates in Ni-Catalyzed Cross-Coupling Reactions

Here we report the use of pulse radiolysis and spectroelectrochemistry to generate low-valent nickel intermediates relevant to synthetically important Ni-catalyzed cross-coupling reactions and interrogate their reactivities toward comproportionation and oxidative addition processes. Pulse radiolysis provided a direct means to generate singly reduced [(dtbbpy)NiBr], enabling the identification of a rapid Ni(0)/Ni(II) comproportionation process taking place under synthetically relevant electrolysis conditions. Furthermore, this approach also permitted the direct measurement of Ni(I) oxidative addition rates with electronically differentiated aryl iodide electrophiles (k OA = 1.3 × 10 4 –2.4 × 10 5 M –1 s –1 ), an elementary organometallic step often proposed in nickel-catalyzed cross-coupling reactions. Together, these results hold implications for a number of Ni-catalyzed cross-coupling processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Mending cracks atom-by-atom in rutile TiO2 with electron beam radiolysis

Abstract Rich electron-matter interactions fundamentally enable electron probe studies of materials such as scanning transmission electron microscopy (STEM). Inelastic interactions often result in structural modifications of the material, ultimately limiting the quality of electron probe measurements. However, atomistic mechanisms of inelastic-scattering-driven transformations are difficult to characterize. Here, we report direct visualization of radiolysis-driven restructuring of rutile TiO 2 under electron beam irradiation. Using annular dark field imaging and electron energy-loss spectroscopy signals, STEM probes revealed the progressive filling of atomically sharp nanometer-wide cracks with striking atomic resolution detail. STEM probes of varying beam energy and precisely controlled electron dose were found to constructively restructure rutile TiO 2 according to a quantified radiolytic mechanism. Based on direct experimental observation, a “two-step rolling” model of mobile octahedral building blocks enabling radiolysis-driven atomic migration is introduced. Such controlled electron beam-induced radiolytic restructuring can be used to engineer novel nanostructures atom-by-atom.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Reactivity of Zn + aq in high-temperature water radiolysis

For this work, reactivity of transients involving Zn + in high-temperature water radiolysis has been studied in the temperature range of 25–300 °C. The reduced monovalent zinc species were generated from an electron transfer process between the hydrated electron and Zn 2+ ions using pulse radiolysis. The Zn + species can subsequently be oxidized by the radiolytically-produced oxidizing species: ˙OH, H 2 O 2 and ˙H. We find that the absorption of monovalent zinc is very sensitive to the pH of the medium. An absorption maximum at 306–311 nm is most pronounced at pH 7 and the signal then decreases in acidic media where the reducing electrons are competitively captured by protons. At pH values higher than 7, hydroxo-forms of Zn 2+ are created and the maximum of the absorption signal begins to shift to the red spectral region. We find that the optical spectrum of Zn + aq cannot be fully explained in terms of a charge-transfer to solvent (CTTS) process, which was previously proposed. Reaction rates of most of the recombination reactions investigated follow the empirical Arrhenius relationship at temperatures up to 200 °C and have been determined at higher temperatures for the first time. A bimolecular disproportionation reaction of Zn + aq is not observed under the conditions investigated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Understanding the mechanisms of anisotropic dissolution in metal oxides by applying radiolysis simulations to liquid-phase TEM

Iron-based redox-active minerals are ubiquitous in soils, sediments, and aquatic systems. Their dissolution is of great importance for microbial impacts on carbon cycling and the biogeochemistry of the lithosphere and hydrosphere. Despite its widespread significance and extensive prior study, the atomic-to-nanoscale mechanisms of dissolution remain poorly understood, particularly the interplay between acidic and reductive processes. Here, we use in situ liquid-phase-transmission electron microscopy (LP-TEM) and simulations of radiolysis to probe and control acidic versus reductive dissolution of akaganeite (β–FeOOH) nanorods. Informed by crystal structure and surface chemistry, the balance between acidic dissolution at rod tips and reductive dissolution at rod sides was systematically varied using pH buffers, background chloride anions, and electron beam dose. We find that buffers, such as bis-tris, effectively inhibited dissolution by consuming radiolytic acidic and reducing species such as superoxides and aqueous electrons. In contrast, chloride anions simultaneously suppressed dissolution at rod tips by stabilizing structural elements while promoting dissolution at rod sides through surface complexation. Dissolution behaviors were systematically varied by shifting the balance between acidic and reductive attacks. The findings show LP-TEM combined with simulations of radiolysis effects can provide a unique and versatile platform for quantitatively investigating dissolution mechanisms, with implications for understanding metal cycling in natural environments and the development of tailored nanomaterials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Gas-phase Radiolysis in Plutonium Dioxide Powder

A sample of PuO 2 powder undergoes self radiolysis, causing water present in the solid to generate hydrogen, oxygen, and minor species (e.g. H 2 O 2 ). This is a matter of concern for stored PuO 2 , since the gases could react exothermically and rupture the container. In experiments at LANL, most PuO 2 /salt samples generate mostly H 2 , but a few samples generate a mixture of H 2 and O 2 together. In these special cases, the mixture of H 2 and O 2 in the pore volumes of the powder will then be subject to radiolysis, causing the reverse reaction H 2 + O 2 $\Rightarrow$ H 2 O. In order to understand the steady-state quantities of these gases, it is necessary to estimate the amount of energy from the alpha irradiation that drives this reaction. This report outlines one possible approach for this process, yielding a value for the fractional amount of radiation deposited in the gas phase of 294 ppm. This corresponds to the case of a powder with porosity of 78%. We then use a comprehensive chemical kinetics model based on elementary gas phase reactions to calculate the rate of conversion back to water. We estimate a reduction in the H 2 pressure of about 12 kPa/month, which applies only when O 2 is simultaneously present in the gas phase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Steady state radiolysis–polyhalide accumulation products [Poster]

The study of steady-state radiolysis of polyhalides is crucial as it simulates the prolonged radiation exposure that materials (e.g., alloys, molten salts) experience in reactor environments. This research provides valuable insights into the long-term effects on material properties, chemical stability, and structural integrity. It is closely linked with fundamental radiation chemistry, which aids in predicting the chemical behavior of accumulation products. Understanding the initial speciation, yield, and chemical evolution of radiolysis products is essential for managing material degradation, controlling corrosion, and ensuring reactor safety.

36 - MATERIALS SCIENCE↗
DOE OSTI2022

Hydroxyl radical yields in the heavy ion radiolysis of water

Scavenging experiments coupled with Monte Carlo track structure and kinetics simulations have been used to determining and understand the yields of hydroxyl radicals in the radiolysis of water with protons and carbon ions. Carbon dioxide production from aerated formic acid solutions with concentrations ranging from 10-3 to 1 mol./dm3 was used as a probe of the time dependence of the hydroxyl radical yield from about 5 ns to 1 ?s. Numerical extrapolation of the results at slightly different ion energies in combination with data from gamma radiolysis experiments allows a systematic analysis of both track average and track segment yields, with considerable track chemistry found to occur on the nanosecond to microsecond time scale. Track chemistry calculations utilizing Monte Carlo track structure simulations and nonhomogeneous independent reaction times diffusion-reaction modeling of product yields reproduce experimental observations. Subsequently, the track simulation methods were used to predict hydroxyl radical kinetics in deaerated and aerated water at neutral pH. Taken with literature data for helium ion beam studies, the results offer insight into the potential for indirect radiation induced damage to biological systems for light ions with very different track structures.

38 - RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCL↗
DOE OSTI2024

Impacts of Neodymium Complexation on Radiolysis of Tetramethyl Diglycolamide (TMDGA) in Aqueous Solutions

Hydrophilic diglycolamides (DGA) ligands have been explored for use as stripping agents in various lanthanide and actinide partitioning processes.1 The separation of lanthanide fission products and transplutonic actinides can serve multifaceted advantages, in that the separation of neutron poisoning rare earth element (REE) fission products from the minor actinides in used nuclear fuel (UNF) can be mutually beneficial to the fundamental research behind REE separations and UNF separations. Considerable efforts have been devoted to understanding the radiation chemistry of hydrophilic DGAs. However, recent studies with lipophilic DGAs have shown that metal ion complexation can promote significant changes in their radiolytic susceptibility.2,3 These effects have been attributed to various parameters, including delocalization of electron density, the presence of radiolytically more susceptible counter ions, and steric hindrance. As such, it is pivotal for these complexation effects to be more thoroughly probed to establish mechanistic knowledge for their effects on hydrophilic DGA molecules. Here we present a time-resolved electron pulse and accumulated gamma dose irradiation study on neodymium ion complexes of tetramethyl diglycolamide (TMDGA) under aqueous solution conditions. References (1) Rostaing, C.; Poinssot, C.; Warin, D.; Baron, P.; Lorrain, B. Development and Validation of the EXAm Separation Process for Single Am Recycling. Procedia Chem. 2012, 7, 367–373. https://doi.org/doi: 10.1016/j.proche.2012.10.057. (2) Horne, G. P.; Conrad, J. K.; McLachlan, J. R.; Rotermund, B. M.; Cook, A. R.; Celis-Barros, C.; Mezyk, S. P. Impact of Lanthanide Complexation and Temperature on the Chemical Reactivity of N,N,N’,N’-Tetraoctyl Diglycolamide (TODGA) with the Dodecane Radical Cation. Phys. Chem. Chem. Phys. 2023, Under Review. (3) Kimberlin, A.; Saint-Louis, G.; Guillaumont, D.; Camès, B.; Guilbaud, P.; Berthon, L. Effect of Metal Complexation on Diglycolamide Radiolysis: A Comparison between Ex Situ Gamma and in Situ Alpha Irradiation. Phys. Chem. Chem. Phys. PCCP 2022, 24 (16), 9213–9228. https://doi.org/10.1039/d1cp05731f.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

Assessing an aqueous flow cell designed for in situ crystal growth under X-ray nanotomography and effects of radiolysis products

Nucleation and growth of minerals has broad implications in the geological, environmental and materials sciences. Recent developments in fast X-ray nanotomography have enabled imaging of crystal growth in solutions in situ with a resolution of tens of nanometres, far surpassing optical microscopy. Here, a low-cost, custom-designed aqueous flow cell dedicated to the study of heterogeneous nucleation and growth of minerals in aqueous environments is shown. To gauge the effects of radiation damage from the imaging process on growth reactions, radiation-induced morphological changes of barite crystals (hundreds of nanometres to ∼1 µm) that were pre-deposited on the wall of the flow cell were investigated. Under flowing solution, minor to major crystal dissolution was observed when the tomography scan frequency was increased from every 30 min to every 5 min (with a 1 min scan duration). The production of reactive radicals from X-ray induced water radiolysis and decrease of pH close to the surface of barite are likely responsible for the observed dissolution. The flow cell shown here can possibly be adopted to study a wide range of other chemical reactions in solutions beyond crystal nucleation and growth where the combination of fast flow and fast scan can be used to mitigate the radiation effects.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Comparing elemental measurements at packaging and after storage for signatures of chloride salt radiolysis

Radiolysis of hydrated alkaline earth chloride salts by alpha radiation from plutonium produces the chloride containing gases HCl and Cl 2 . These gases are known to diffuse out of the plutonium-containing material and contribute to corrosion outside of the convenience container. The alkaline earth elements remain with the plutonium-containing material as oxides or hydroxides. The amount of chlorine within the material after storage will be reduced compared to the amount at packaging. The fraction of the alkaline earth elements that are soluble after storage will be reduced compared to the amount at packaging. These signatures may be observable by comparing the chemical analysis measurements made at packaging and after storage. Comparison of measurements on a single Hanford container shows that the chloride does decrease and the alkaline earth elements have reduced solubility in water. Differences seen with other elements make conclusions difficult.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Mini-Canister Radiolysis Testing of ASNF Materials and Surrogates

An experimental irradiation campaign to investigate radiolysis behavior of ASNF was conducted using in situ gas monitoring of small, sealed stainless-steel vessels (mini-canisters) containing aluminum samples with adherent (oxy)hydroxide films under helium backfill. The samples were irradiated with gamma radiation from a Co-60 irradiator. The samples tested included aluminum plate assemblies with lab-grown (oxy)hydroxides as surrogates for fuel as well as an end cropping from an actual ASNF assembly retrieved from long-term wet storage. These experiments enabled investigation of the impacts of various fuel drying approaches on the radiolytic generation rate and measurement of the H 2 yield associated with a reactor exposed sample with reactor-formed (oxy)hydroxide. The resulting data can be incorporated into model development for ASNF in dry storage. This report presents the cumulative results from four surrogate assemblies tested after application of different preparation (drying) conditions as well as the ASNF cropping; some post-irradiation testing was included. The mini-canister results are compared to data from related experimental campaigns that also tested the impact of drying conditions using samples irradiated in glass ampoules and discusses implications of the combined data

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2026

Radiolytic degradation of n -dodecane: Insights from time resolved pulsed electron radiolysis using aromatic scavengers

This study uses time-resolved picosecond pulsed electron radiolysis and transient absorbance spectroscopy to investigate early radiolytic processes in n-dodecane, a prototypical organic solvent for reprocessing used nuclear fuel (UNF). The primary radical cation, solvated electron, and excited states in neat n-dodecane are formed and consumed on timescales that are difficult to observe directly. Aromatic solutes, biphenyl and benzophenone, were utilized as scavengers to convert these short-lived species into longer-lived, optically detectable transient products to serve as indirect probes of the fraction of the initial n-dodecane radiolytic products that can be intercepted before undergoing ultrafast decay or competing reactions. The transient absorbance spectra of these scavengers and their radiolytic products were analyzed. Results indicate that while biphenyl and benzophenone effectively capture several radiolytic species, they do not fully scavenge all n-dodecane excited states, suggesting potential inefficiencies or additional side reactions. This study provides insight into the formation and accessibility of radiation-induced excited states and charge carriers in n-dodecane, which play a key role in the degradation of solvent extraction systems used in UNF reprocessing.

58 GEOSCIENCES↗