Careful manipulation of the plutonium oxidation states is essential in the study and utilization of its rich redox chemistry. To achieve this level of control, a comprehensive mechanistic understanding of radiation-induced plutonium redox chemistry is critical due to the unavoidable exposure of plutonium to ionizing radiation fields, both inherent and from in-process applications. To this end, we have developed an experimentally evaluated multiscale computer model for the prediction of gamma radiation-induced Pu(IV) redox chemistry in concentrated nitric acid solutions (1.0, 3.0, and 6.0 M). Under these acidic, aqueous solution conditions, cobalt-60 gamma irradiation afforded marginal net conversion of Pu(IV) to Pu(VI), the extent of which was dependent on the concentration of HNO3 and absorbed gamma dose. Multiscale calculations, which are in excellent agreement with experimental data, indicate that this observation is due to a combination of inherent plutonium disproportionation reactions and several radiation-induced processes, including redox cycling between Pu(IV) and Pu(III), as achieved by the reduction of Pu(IV) by nitrous acid and hydrogen peroxide, the oxidation of Pu(III) by nitrate and hydroxyl radicals, and the sequential oxidation of Pu(IV) to Pu(V) and Pu(VI) by the remaining available yield of nitrate radicals.

Over 60 samples of plutonium dioxide (PuO2) powders of varying provenance have been exposed to humid atmospheres and the hydrogen (H2) generation rates measured by gas chromatography. The effects of relative humidity (RH), specific surface area (SSA), plutonium isotopic composition (absorbed dose), and overlying atmosphere have been investigated for ‘as received’ PuO2 powders from the United Kingdom’s Thorp and Magnox reprocessing plants, high surface area powder produced in the laboratory and Magnox PuO2 that was recalcined at 800, 900 or 950°C. Hydrogen generation was shown to be susceptible to subtle influences with the most consistent results observed at 95% RH. However, it was shown that the measured (net) hydrogen decreases with decreasing RH and with atmosphere in the order: Air > argon > nitrogen. There was no clear effect of SSA, apart from with the highest SSA samples (∼40 m2.g−1) but these powders also have very different morphology, porosity, and carbon content to the rest. The results presented substantially enhance the growing body of literature on the factors that determine hydrogen and gas generation from PuO2 that has significant implications for long term safe storage of plutonium globally.

Acetohydroxamic acid (AHA) has been proposed for inclusion in advanced, single-cycle, used nuclear fuel reprocessing solvent systems for the reduction and complexation of plutonium and neptunium ions. For this application, a detailed description of the fundamental degradation of AHA in dilute aqueous nitric acid is required. To this end, we present a comprehensive, multiscale computer model for the coupled radiolytic and hydrolytic degradation of AHA in aqueous sodium nitrate and nitric acid solutions. Rate coefficients for the reactions of AHA and hydroxylamine (HA) with the oxidizing nitrate radical were measured for the first time using electron pulse radiolysis and used as inputs for the kinetic model. The computer model results are validated by comparison to experimental data from steady-state gamma ray irradiations, for which the agreement is excellent. The presented model accurately predicts the yields of the major degradation products of AHA: acetic acid, HA, nitrous oxide, and molecular hydrogen.

The Cover Feature represents acetohydroxamic acid degradation in used nuclear fuel reprocessing cycles, where it is broken down by hydrolysis and radiation in aqueous nitric acid to form acetic acid, hydroxylamine, nitrous oxide, and hydrogen gas. Designed by Rett Longmore. More information can be found in the Research Article by Jacy K. Conrad, Gregory P. Horne and co-workers.

The effects of ion beam irradiation on aqueous suspensions of metal oxides has received relatively little attention compared to gamma-ray irradiation despite being a highly prevalent process in spent nuclear fuel storage and reprocessing. This is partly due to the difficulties associated with homogeneously irradiating condensed-phase matter using alpha-particles. Here, we report experimental yields of H-2 from the 5.5 MeV He2+ ion irradiation of aqueous suspensions of ZnO nanoparticles. The obtained results are compared to our previously measured results for the.-radiolysis of the same system. The amount of H-2 increases linearly with adsorbed dose for all studied concentrations. The measured yields are of the same order of magnitude as those observed for pure water, but decrease with increasing water content. Overall, the yields follow a similar trend to those observed for gamma-ray radiolysis.

Molten chloride salts are currently under consideration as combined coolant and liquid fuel for next-generation molten salt nuclear reactors. Unlike complementary light-water reactor technologies, the radiation science underpinning molten salts is in its infancy, and thus requires a fundamental mechanistic investigation to elucidate the radiation-driven chemistry within molten salt reactors. Here we present an electron pulse radiolysis kinetics study into the behaviour of the primary radiolytic species generated in molten chloride systems, i.e., the solvated electron (eS-) and di-chlorine radical anion (Cl2˙-). We examine the reaction of eS- with Zn2+ from 400-600 °C (Ea = 30.31 ± 0.09 kJ mol-1), and the kinetics and decay mechanisms of Cl2˙- in molten lithium chloride-potassium chloride (LiCl-KCl) eutectic. In the absence of Zn2+, the lifetime of eS- was found to be dictated by residual impurities in ostensibly "pure" salts, and thus the observed decay is dependent on sample history rather than being an intrinsic property of the salt. The decay of Cl2˙- is complex, owing to the competition of Cl2˙- disproportionation with several other chemical pathways, one of which involves reduction by radiolytically-produced Zn+ species. Overall, the reported findings demonstrate the richness and complexity of chemistry involving the interactions of ionizing radiation with molten salts.

In situ monitoring of corrosion processes is important to fundamentally understand the kinetics and evolution of materials in harsh environments. A quasi in situ transmission electron microscopy technique was utilized to study microstructural and chemical evolution of a Ni-20Cr disc sample exposed to molten KCl-MgCl2 salt for 60 s in consecutive 20 s iterations. In situ synchrotron X-ray nano-tomography was performed to characterize the morphological evolution of a Ni-20Cr microwire exposed to molten KCl-MgCl2. Both techniques captured key corrosion events and revealed mechanisms at different time and length scales, potentially bringing greater insights and deeper understanding beyond conventional analysis.

The electron paramagnetic resonance and diffuse reflectance-optical absorption spectra of room-temperature gamma-irradiated KCl-MgCl2 binary solid salt mixtures (98:2 mol % and 2:98 mol %) and the eutectic (68:32 mol %) are reported. Additionally, powder X-ray diffraction of the pristine salts and thermal annealing studies of the irradiated salts were performed to evaluate the radiolysis product stability, annihilation, and association in metallic particles. The main long-lived transient species detected in 98:2 mol % KCl-MgCl2 salts were perturbed F-centers, that is, trapped electrons (e(t)(-)) in the vicinity of Mg ions (lambda(max) at 561 nm), and the radiolytic reduction of Mg2+ to Mg+ and Mg-0. Thermal annealing promoted the diffusion of defects to yield polycations (Mg-n(+)). On the other hand, irradiation of 2:98 mol % KCl-MgCl2 salts showed the formation of cationic and neutral Mg dimers (Mg-2(+) and Mg-2) and trimers as well as centers with a rhombic powder pattern apparently consisting of an electron shared between three Mg2+ nuclei associated with an anion vacancy (v(a)(+)-Mg-3(5+)). Trapped electrons (e(t)(-)) (F-centers) were not observed in the irradiated eutectic mixture; instead, Mg-2, Mg-0, and Cl-3(-) were observed. It was observed that the higher temperature for thermal ionization of radiation-reduced Mg species decreased the extent of electron recombination reactions and the disproportionation of Cl-3(-) compared to the pure KCl but enhanced the aggregation of Mg into larger metallic microstructures (metallic particles).

Acetohydroxamic acid (AHA) is a small organic acid with a wide variety of industrial, biological, and pharmacological applications. A deep fundamental molecular level understanding of the mechanisms responsible for the radical-induced reactions of AHA in these environments is necessary to predict and control their behaviour and elucidate their interplay with other attendant chemical species, for example, the oxidative degradation products of AHA. To this end, we present a comprehensive, multiscale computer model for interrogating the radical-induced degradation of AHA in acidic aqueous solutions. Model predictions were critically evaluated by a systematic experimental radiation chemistry investigation, leveraging time-resolved electron pulse irradiation techniques for the measurement of new radical reaction rate coefficients, and steady-state gamma irradiations for the identification and quantification of AHA degradation products: acetic acid, hydroxylamine, nitrous oxide, and molecular hydrogen, with formic acid and methane as minor products. Excellent agreement was achieved between calculation and experiment, indicating that this fundamental model can accurately predict the degradation pathways of AHA under irradiation in acidic aqueous solutions.

Room temperature post-irradiation measurements of diffuse reflectance and electron paramagnetic resonance spectroscopies were made to characterize the long-lived radiation-induced species formed from the gamma irradiation of solid KCl, MgCl2, and ZnCl2 salts up to 100 kGy. The method used showed results consistent with those reported for electron and gamma irradiation of KCl in single crystals. Thermal bleaching of irradiated KCl demonstrated accelerated disaggregation of defect clusters above 400 K, due to decomposition of Cl3-. The defects formed in irradiated MgCl2 comprised a mixture of Cl3-, F-centers, and Mg+ associated as M-centers. Further, Mg metal cluster formation was also observed at 100 kGy, in addition to accelerated destruction of F-centers above 20 kGy. Irradiated ZnCl2 afforded the formation of Cl2- due to its high ionization potential and crystalline structure, which decreases recombination. The presence of aggregates in all cases indicates the high diffusion of radicals and the predominance of secondary processes at 295 K. Thermal bleaching studies showed that chloride aggregates' stability increases with the ionization potential of the cation present. The characterization of long-lived radiolytic transients of pure salts provides important information for the understanding of complex salt mixtures under the action of gamma radiation.

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

This article describes the radiation facilities and associated sample preparation, management, and analysis equipment currently in place at the Dalton Cumbrian Facility, a facility which opened in 2011 to support the UK’s nuclear industry. Examples of measurements performed using these facilities are presented to illustrate their versatility and the breadth of research they make possible. Results are presented from research which furthers our understanding of radiation damage to polymeric materials, radiolytic yield of gaseous products in situations relevant to nuclear materials, radiation chemistry in light water reactor cooling systems, material chemistry relevant to immobilization of nuclear waste, and radiation-induced corrosion of fuel cladding elements. Applications of radiation chemistry relevant to health care are also described. Research concerning the mechanisms of radioprotection by dietary carotenoids is reported. An ongoing open-labware project to develop a suite of modular sample handling components suited to radiation research is described, as is the development of a new neutron source able to provide directional beams of neutrons.

This work utilizes electron energy loss spectroscopy (EELS) to identify oxidation state of alloying elements in Ni-based alloys after exposure to molten chloride salt systems. Pure Ni and Ni-20Cr model alloy were corroded in molten ZnCl2 and KCl-MgCl2 under argon atmosphere at various temperatures. Oxidation states of Cr (Cr3+) and Ni (Ni2+) in the molten salt after corrosion were determined by monitoring changes in the L2,3 edges of corresponding EELS spectra. Oxidation state mapping technique using principal component analysis and multiple linear least squares fitting in HyperSpy Python package was developed.

The yields of hydroxyl radicals in the radiolysis of water with protons and carbon ions have been examined using experimental scavenging techniques coupled with Monte Carlo track simulations. Combined with previous results using helium ions, this set of data gives valuable information on the potential for radiation induced damage to biological systems for light ions with very different track structures. Carbon dioxide production from aerated formic acid solutions in concentrations ranging from 10-3 to 1 M was used as a probe of hydroxyl radical yields from about 6 ns to 818 ns. Numerical interpolation of the results at slightly different ion energies in combination with data from gamma radiolysis allows for a systematic analysis of both track average and track segment yields. As expected, considerable track chemistry is found to occur on the nanosecond to microsecond time scales. Monte Carlo track simulations employing stochastic diffusion-kinetic calculations of product yields are found to reproduce experimental observations satisfactorily. The track simulations are used to extract hydroxyl radical kinetics in pure water at neutral conditions.

The Nuclear Science User Facilities (NSUF) first gathered and reported metric data for Fiscal Year (FY) 2014. The goal of the FY 2014 NSUF Metric Report was to establish metric measures and to provide baseline data to evaluate future performance of the NSUF. Each metric goal and objective was established through NSUF discussions with Department of Energy (DOE) Idaho Operations Office and Office of Nuclear Energy staff. This report provides the data, analysis, and conclusions for the FY 2020 metrics.

To facilitate the development of molten salt reactor technologies, a fundamental understanding of the physical and chemical properties of molten salts under the combined conditions of high temperature and intense radiation fields is necessary. Optical spectroscopic (UV-Vis-near IR) and electrochemical techniques are powerful analytical tools to probe molecular structure, speciation, thermodynamics, and kinetics of solution dynamics. Here, we report the design and fabrication of three custom-made apparatus: (i) a multi-port spectroelectrochemical furnace equipped with optical spectroscopic and electrochemical instrumentation, (ii) a high-temperature cell holder for time-resolved optical detection of radiolytic transients in molten salts, and (iii) a miniaturized spectroscopy furnace for the investigation of steady-state electron beam effects on molten salt speciation and composition by optical spectroscopy. Initial results obtained with the spectroelectrochemical furnace (i) and high-temperature cell holder (ii) are reported.

A novel method has been implemented to prepare metal oxide nanopowders covered with known quantities of adsorbed water; we subsequently studied the γ-radiolysis of ZrO2 nanopowders covered with H2O layers. H2 yields from the adsorbed water radiolysis are of importance in multiple industrial contexts – the nuclear industry being a prime example. Measured H2 yields at water coverages of just below and above one monolayer are around 350 times greater than for neat water, but these yields decrease rapidly with increasing water loading of the ZrO2 nanoparticles, approaching the yield of bulk water at coverages of tens of water layers. The observed plateau of the yields at 0.5 to 2.0 monolayers coverage can be explained by the ease with which electronic excitations in the ZrO2 can be transferred across the interface to the first one or two adsorbed water layers. However, with increasing water loading, energy transfer to water layers further away from the interface becomes less efficient, and above ~30 water layers, most of the water is not affected by any exciton formation in the ZrO2.

Molten Salt Reactors (MSRs) are a potential game-changing technology for next-generation nuclear power. Although the MSR concept was demonstrated at Oak Ridge National Laboratory (ORNL) in the 1960’s, it had not gathered attention from commercial vendors until recently. A fundamental knowledge of salt chemistry, including the speciation and solubility of corrosion and fission products is central to the safe and reliable operation of MSRs. The structural properties of fused salt solutions, especially the coordination geometry around the metal ions in the melt, are intricately dependent on the melt composition and temperature. In this work, a combination of in-situ electrochemistry and optical absorption spectroscopy techniques are utilized to understand the speciation and structure of lanthanides in molten chloride salts as a function of temperature, concentration and melt composition. The spectroelectrochemistry of metal species in molten salt media can be used as a potential process monitoring technique enabling the quantitative measurement of lanthanide and actinide metals within molten salt reactors or nuclear fuel pyro-processing applications. This work was supported as part of the Molten Salts in Extreme Environments Energy Frontier Research Center, funded by the U.S. Department of Energy (US-DOE), Office of Science, Basic Energy Sciences, at BNL, INL and ORNL under contracts DE-SC0012704, DE-AC07-05ID14517 and DE-FC02-04ER15533, respectively.

A thorough understanding of radiation effects on molten salt media is necessary to support the design, development, and deployment of molten salt reactor, using either fuel salt or solid fuel with salt as the coolant. Fundamental issues include the determination of the initial yields and reactivity of the primary radiolytic species, i.e., the solvated electron (esolv –), chlorine atom (Cl•), and dichloride radical anion (Cl2 •–) as their reactivity varies depending on the environment such as the salt cation and temperature. Here we report on the reaction kinetics for esolv – and Cl2 •– in molten LiCl-KCl eutectic doped with Zn2+ ions. Electron pulse radiolysis absorption spectroscopy was used to observe the transient behavior of esolv – and Cl2 •– on the nanosecond to microsecond time scale. Experiments were performed using the Brookhaven National Laboratory Laser-Electron Accelerator Facility (LEAF)1 and utilizing a recently developed high-temperature sample holder.2 Decay kinetics of of esolv – and Cl2 •– in 9.41 mM ZnCl2 in LiCl-KCl are shown in the figure. esolv – and Cl2 •– decays in different time scale due to different reaction kinetics and decay speed increase as temperature. This work was supported as part of the Molten Salts in Extreme Environments Energy Frontier Research Center, funded by the U.S. Department of Energy (US-DOE), Office of Science, Basic Energy Sciences, at BNL, INL and ORNL under contracts DE-SC0012704, DE-AC07-05ID14517 and DE-FC02-04ER15533, respectively. The Laser Electron Accelerator Facility of the BNL Accelerator Center for Energy Research is supported by the US-DOE Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under contract DE-SC0012704. Wishart, J. F.; Cook, A. R.; Miller, J. R.; Rev. Sci. Instrum., 2004, 75 (11), 4359. Phillips, W. C.; Layne, B.; Gakhar, R.; Horne, G. P.; Ramos-Ballesteros, A.; Iwamatsu, K.; LaVerne, J. A.; Pimblott, S. M.; Wishart, J. F.; Rev. Sci. Instrum., 2019, in peer review. Figure 1