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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Materials Data on HNO3 by Materials Project

HNO3 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of eight nitric acid molecules. N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.22–1.38 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.01 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the third O2- site, O2- is bonded in a water-like geometry to one N5+ and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HNO3 by Materials Project

HNO3 crystallizes in the monoclinic P2_1 space group. The structure is zero-dimensional and consists of sixteen nitric acid molecules. N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.22–1.38 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.01 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a water-like geometry to one N5+ and one H1+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one N5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Leveraging design of experiments to build chemometric models for the quantification of uranium (VI) and HNO3 by Raman spectroscopy

Partial least squares regression (PLSR) and support vector regression (SVR) models were optimized for the quantification of U(VI) (10–320 g L −1 ) and HNO 3 (0.6–6 M) by Raman spectroscopy with optimized calibration sets chosen by optimal design of experiments. The designed approach effectively minimized the number of samples in the calibration set for PLSR and SVR by selecting sample concentrations with a quadratic process model, despite complex confounding and covarying spectral features in the spectra. The top PLS2 model resulted in percent root mean square errors of prediction for U(VI), HNO 3 , and NO 3 − of 3.7%, 3.6%, and 2.9%, respectively. PLS1 models performed similarly despite modeling an analyte with a majority linear response (i.e., uranyl symmetric stretch) and another with more covarying vibrational modes (i.e., HNO 3 ). Partial least squares (PLS) model loadings and regression coefficients were evaluated to better understand the relationship between weaker Raman bands and covarying spectral features. Support vector machine models outperformed PLS1 models, resulting in percent root mean square error of prediction values for U(VI) and HNO 3 of 1.5% and 3.1%, respectively. The optimal nonlinear SVR model was trained using a similar number of samples (11) compared with the PLSR model, even though PLS is a linear modeling approach. The generic D-optimal design presented in this work provides a robust statistical framework for selecting training set samples in disparate two-factor systems. This approach reinforces Raman spectroscopy for the quantification of species relevant to the nuclear fuel cycle and provides a robust chemometric modeling approach to bolster online monitoring in challenging process environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Optimization of Cation Exchange for the Separation of Actinium-225 from Radioactive Thorium, Radium-223 and Other Metals

Actinium-225 (225Ac) can be produced with a linear accelerator by proton irradiation of a thorium (Th) target, but the Th also underdoes fission and produces 400 other radioisotopes. No research exists on optimization of the cation step for the purification. The research herein examines the optimization of the cation exchange step for the purification of 225Ac. The following variables were tested: pH of load solution (1.5–4.6); rinse steps with various concentrations of HCl, HNO3, H2SO4, and combinations of HCl and HNO3; various thorium chelators to block retention; MP50 and AG50 resins; and retention of 20–45 elements with different rinse sequences. The research indicated that HCl removes more isotopes earlier than HNO3, but that some elements, such as barium and radium, could be eluted with ≥2.5 M HNO3. The optimal pH of the load solution was 1.5–2.0, and the optimized rinse sequence was five bed volumes (BV) of 1 M citric acid pH 2.0, 3 BV of water, 3 BV of 2 M HNO3, 6 BV of 2.5 M HNO3 and 20 BV of 6 M HNO3. The sequence recovered >90% of 225Ac with minimal 223Ra and thorium present.

223Ra↗
DOE OSTI2025

Generation and Study of Am(IV) by Temperature-Controlled Electron Pulse Radiolysis

Used nuclear fuel (UNF) separation techniques that strive to separate radiotoxic americium (Am) from trivalent lanthanide fission products through oxidation state control have increased research efforts surrounding Am(V) and Am(VI). However, equivalent knowledge of the tetravalent state, Am(IV), has remained elusive, particularly in conditions more representative of UNF reprocessing, i.e., in concentrated nitric acid (HNO3). With this in mind, we have used electron pulse radiolysis to study the radiation-induced redox reaction of Am(III) with the oxidizing nitrate radical (NO3?) in 6 M HNO3: Am(III) + NO3? ? Am(IV) + NO3? . These experiments enabled us to observe the growth and decay of Am(IV) in a concentrated acidic solution for the first time. The transient Am(IV) species was found to have a lifetime of ~16 µs?sufficiently long-lived to play a critical mechanistic role in UNF reprocessing systems. Additionally, we performed the first-ever temperature-dependent kinetics study of an actinide element, elucidating unprecedented Arrhenius and Eyring activation parameters for the reaction of Am(III) with NO3?. This new knowledge provides much-needed molecular-level insights into the radiation-induced behavior of Am.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2017

Nitric Acid and Water Extraction by T2EHDGA in n -Dodecane

Liquid-liquid distribution behavior of nitric acid (HNO3) and water by a diglycolamide ligand, N,N,N',N'-tetra-2-ethylhexyldiglycolamide (T2EHDGA) into n-dodecane diluent was investigated. Spectroscopic FTIR and NMR characterization of the organic extraction solutions indicate T2EHDGA carbonyl coordinates HNO3 and progressively aggregates at high acid conditions. Water extraction increases in the presence of HNO3. The experimentally observed distribution of HNO3 was modeled using the computer program, SXLSQI. The results indicated that the formation of two organic phase species—HNO3·T2EHDGA and (HNO3)2·T2EHDGA—satisfactory describes the acid transport behavior. Temperature dependent solvent extraction studies allowed for determination of thermodynamic extraction constants and ΔH and ΔS parameters for the corresponding extractive processes.

Campbell, Emily L.↗
DOE OSTI2018

Extraction Behavior of Ln(III) ions by T2EHDGA/n-dodecane from Nitric acid and Sodium Nitrate Solutions

The diglycolamide extractant, T2EHDGA, has proven promising for the separation of lanthanides and minor actinides in high-level nuclear waste reprocessing. This neutral extractant has shown significant extraction capacity for HNO3 into the non-polar organic phase, along with hyper-stoichiometric nitrate dependence on extraction of trivalent f-elements. The transport behavior of T2EHDGA/n-dodecane toward trivalent lanthanides is not well understood. This work found a significant increase in distribution measurements for Eu(III) extracted from aqueous HNO3 media as compared to NaNO3. The extraction of Eu(III) from HNO3 results in a different thermodynamic product than predicted by classic solvent extraction of 3:1 ligand-metal complex as observed with NaNO3 in FTIR and UV-vis spectroscopy. Experimental distribution measurements in conjunction with the solvent extraction modeling program, SXLSQI, suggest participation of 1- to 2 HNO3 molecules in the Eu(III)/T2EHDGA complex when extracted from HNO3 media, indicative of a mechanism change responsible for the enhanced extraction behavior toward lanthanides in the presence of HNO3.

Campbell, Emily L.↗
DOE OSTI2019

Modifications of Textured Silicon Surface Morphology and Its Effect on Poly-Si/SiO x Contact Passivation for Silicon Solar Cells

High-efficiency crystalline silicon (c -Si) solar cells require textured surfaces for efficient light trapping. However, passivation of a textured pyramidal surface to reduce carrier recombination is challenging due to the presence of sharp tips, edges, and valleys. Using electrical and surface microscopies combined with lifetime measurements, we report on the effect of HF:HNO3 etching on the pyramidal textured Si surface morphology, and on poly-Si/SiOx contact performance. Preferential rounding of either the valleys between pyramids, or the pyramid tips is obtained depending on the HF:HNO3 solution temperature. Both these morphologies make the pyramid shape irregular, with the pyramid faces no longer being predominantly a Si(111) surface. Our atomic force microscopy measurements further show that the nanoscale roughness over the pyramid face also reduces after HF:HNO3 etching. Thus, etching affects the microscopic pyramidal shape, the dominant crystallographic orientation, and the nanoscale roughness of the surface. We speculate that these three surface effects result in the improvement of surface passivation via poly-Si/SiOx contacts. However, this improved passivation is accompanied by increased reflectance of the HF:HNO3-etched textured surface. Finally, our electron-beam-induced current measurements reveal thickness nonuniformities in the thermally grown SiOx layer on the HF:HNO3-etched textured Si surface: SiO x is thicker near the pyramid tips, edges, and faces as compared with near the valleys between pyramids. This nonuniformity in the SiOx layer may explain the poorer passivation obtained on a KOH-textured and HF:HNO3-etched textured surface as compared with a planar surface.

14 SOLAR ENERGY↗
DOE OSTI2026

Irradiation Impact on Uranium Recovery Under Direct Extraction Conditions

Reducing the quantity of high-level radioactive waste is essential for minimizing environmental impact and improving efficiency of using natural resources for nuclear power. The current standard, Plutonium Uranium Solvent EXtraction (PUREX), uses tributyl phosphate (TBP) ligands to extract complexes of uranium and plutonium from a nitric acid (HNO3) phase. Although this method is effective, large volumes of HNO3 and the non-incinerable phosphate ligands increase the amount of hazardous waste produced. Alternative extractants and flowsheets have been proposed that allow for more selective extraction of radioactive metals, reduced nitric acid use, and easier incineration by only containing carbon, hydrogen, oxygen, and nitrogen (CHON). One candidate, N,N-di(2-ethylhexyl)-isobutyramide (DEHiBA) exhibits promising properties for direct extraction. A HNO3 pre-equilibrated DEHiBA phase selectively extracts U(VI), leaving plutonium, transuranics, and fission products behind as precipitate and reducing the volume of radioactive HNO3 produced.

38 - RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCL↗
DOE OSTI2018

Development and testing of a novel micro-Raman probe and application of calibration transfer method for the quantitative analysis of microfluidic nitric acid streams

To simplify and improve the safety of reprocessing used nuclear fuel, an initial assessment was made of Raman microscopy applied to microfluidic volumes with a view toward the on-line spectroscopic measurement of highly radioactive solutions. This study compares a microscopic Raman probe (excitation focal point diameter 70 µm) to a larger, well studied probe (excitation focal point diameter 125 µm) used in prior investigations. This was done by chemometrically modeling and predicting concentrations of HNO3 solutions (0 M to 8 M) as they flowed through microfluidic cells based upon spectra from each probe. Spectra recorded for each probe using the same static HNO3 solution set contained in 2 dram glass vials were used as training sets to produce models for the respective probes. Modeling required baseline, normalization and smoothing preprocessing to compensate for a reduced path length between the static glass vial training set (4 cm) and the reduced path length flow cell (1 cm), wide ranging solution concentrations, and the associated non-linear spectral changes, and abrupt and uneven concentration changes of flowing solutions. The micro-Raman probe is able to produce spectra that may be analyzed chemometrically to accurately predict the concentration of flowing HNO3 solutions down to microliter volumes. Based upon RMSECV and RMSEP modeling statistics concentration predictions of the micro-Raman probe are comparable to those obtained for a macro-Raman on identical samples.

microscopic Raman probe, MicroRaman, nitric acid, ↗
DOE OSTI2024

H-Canyon Flowsheet for the Neutralization of Dissolved Fast Critical Assembly (FCA) Fuel

The H-Canyon facility will be dissolving unirradiated stainless-steel clad Fast Critical Assembly (FCA) fuel in HNO3 and neutralizing the resulting solution with 50 wt% NaOH with no recovery operations prior to transfer to the Concentration, Storage, and Transfer Facility (CSTF). There are two types of FCA fuel, including a Pu-Al metal alloy and a mixed U and Pu oxide. H-Canyon anticipates dissolving 16 batches of the metal fuel and two batches of the oxide fuel. Potassium fluoride will be added to the dissolver solution at 0.05 M to promote dissolution. Gadolinium will be added after the dissolution as a thermal neutron poison for criticality control. H-Canyon requested that SRNL evaluate Gd:239Pu equivalent (239PuEq) ratios of 1:1 and 10:1. The neutralization process precipitates metals including actinides, Gd, and cladding components resulting in a slurry. Caustic neutralization is a routine H-Canyon operation, but the FCA dissolver solution will be unique relative to solutions that are typically processed due to the stainless-steel components, high HNO3 concentration of ~8.5 M, and an initial Pu concentration of up to 4 g/L. Previous neutralization studies have been performed for Pu containing solutions but at less than half the initial Pu concentration and much lower initial HNO3 concentrations. Experimental neutralizations targeted a final free hydroxide (OH-) concentration of 0.6 M as this was anticipated to be the final endpoint, but H-Canyon now expects the endpoint to be 1.2 M OH-. The purpose of this study was to characterize the distribution of the actinide, Gd, and cladding components between the precipitate and supernate, determine if the slurry will back up in the header during the transfer to the CSTF, and determine if solids will settle in the pipeline during the transfer.

Mills, Matthew S.↗
DOE OSTI2021

Fine Aerosol Acidity and Water during Summer in the Eastern North Atlantic

Aerosol pH governs many important atmospheric processes that occur in the marine boundary layer, including regulating halogen and sulfur chemistries, and nutrient fertilization of surface ocean waters. In this study, we investigated the acidity of PM1 over the eastern North Atlantic during the Aerosol and Cloud Experiments in Eastern North Atlantic (ACE-ENA) aircraft campaign. The ISORROPIA-II thermodynamic model was used to predict PM1 pH and water. We first investigated the sensitivities of PM1 pH and water predictions to gas-phase NH3 and HNO3 concentrations. Our sensitivity analysis indicated that even though NH3 and HNO3 were present at very low concentrations in the eastern North Atlantic during the campaign, PM1 pH calculations can still be sensitive to NH3 concentrations. Specifically, NH3 was needed to constrain the pH of populations of PM1 that had low mass concentrations of NH4+ and non-volatile cations (NVCs). We next assumed that gas-phase NH3 and HNO3 concentrations during the campaign were 0.15 and 0.09 µg m−3, respectively, based on previous measurements conducted in the eastern North Atlantic. Using the assumption that PM1 were internally mixed (i.e., bulk PM1), we determined that PM1 pH ranged from 0.3–8.6, with a mean pH of 5.0 ± 2.3. The pH depended on both Hair+ and Wi. Hair+ was controlled primarily by the NVCs/SO42− molar ratio, while Wi was controlled by the SO42− mass concentration and RH. Changes in pH with altitude were driven primarily by changes in SO42−. Since aerosols in marine atmospheres are rarely internally mixed, the scenario where non-sea salt species and sea-salt species were present in two separate aerosol modes in the PM1 (i.e., completely externally mixed) was also considered. Smaller pH values were predicted for the aerosol mode comprised only of non-sea salt species compared to the bulk PM1 (difference of around 1 unit on average). This was due to the exclusion of sea-salt species (especially hygroscopic alkaline NVCs) in this aerosol mode, which led to increases in Hair+ values and decreases in Wi values. This result demonstrated that assumptions of aerosol mixing states can impact aerosol pH predictions substantially, which will have important implications for evaluating the nature and magnitude of pH-dependent atmospheric processes that occur in the marine boundary layer.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

The radiolysis of CMPO: effects of acid, metal complexation and alpha vs. gamma radiation

Abstract The group actinide/lanthanide complexing agent octylphenylcarbamoylmethyl phosphine oxide (CMPO) has been examined for its radiation stability by measuring the kinetics of its reactions with free radicals in both the aqueous and organic phases for the free and metal-complexed ligand, identifying its degradation products for both alpha and gamma irradiation, measuring the effects on solvent extraction performance, and measuring the G-values for its degradation under various conditions. This includes the G-values for CMPO in the absence of, and in contact with the acidic aqueous phase, where it is shown that the acidic aqueous phase provides radio-protection for this ligand. It was found that both solvent and metal complexation affect the kinetics of the reaction of the •NO3 radical, a product of HNO3 radiolysis, with CMPO. For example, CMPO complexed with lanthanides has a rate constant for this reaction an order of magnitude higher than for the free ligand, and the reaction for the free ligand in the organic phase is about three times faster than in the aqueous phase. In steady state radiolysis kinetics it was determined that HNO3, although not NO3- anion, provides radio-protection to CMPO, with the G-value for its degradation decreasing with increasing acidity, until it was almost completely suppressed by irradiation in contact with 5 M HNO3. The same degradation products were produced by irradiation with alpha and gamma-sources, except that the relative abundances of these products varied. For example, the product of C-C bond scission was produced only in low amounts for gamma-radiolysis, but it was an important product for samples irradiated with a He ion beam. These results are compared to the new data appearing in the literature on DGA radiolysis, since CMPO and the DGAs both contain the amide functional group.

CMPO↗
DOE OSTI2023

Milestone 1.2.13: Preliminary Measurements of Radiolytic Nitric Acid Formation to Support Predictive Model Validation

Predictive computational models have been developed to support the technical basis for extended dry storage of aluminum-clad spent nuclear fuel (ASNF) in helium-backfilled cannisters. To date, these models have been optimized on a variety of irradiation experiments designed to elucidate the radiation-induced formation of molecular hydrogen gas, a radiolysis product that is potentially problematic for the safe storage of ASNF. However, the yield of nitric acid (HNO3) has not been determined, despite conservative predictions of its formation (300–4000 ppm) in 1% residual air environments irradiated in contact with ASNF. HNO3, another problematic radiolysis product, can lead to enhanced corrosion and potentially compromise storage canister integrity. Thus, to support the validation of predictive computer models, we report the measurement and quantification of HNO3 from the gamma irradiation of aluminum alloy coupons in humid air.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Batch and column studies of radium, actinium, thorium and protactinium on CL resin in nitric acid, hydrochloric acid and hydrofluoric acid

CL resin (TrisKem International) was characterized for separations of radium, actinium, thorium and protactinium. Batch studies are presented for radium, actinium and thorium in HCl and HNO3 as well as for radium, thorium and protactinium in HF. The uptake of thorium from dilute HNO3 (≤ 10 -4 M) and dilute HCl (≤ 10 -4 M) was found to be very high (D w > 100 in HNO 3 and > 1000 in HCl). Kinetics studies on thorium were performed in HCl and HNO 3 to determine suitably for column separations. Six column separation studies are presented including the separation of trace thorium from radium and actinium in dilute HCl and HNO 3 , the separation of radium from 1 mg 232 Th in dilute HCl, the separation of thorium and radium in the presence of HCl and excess Cl-, the separation of radium, protactinium and thorium by retention of protactinium and the separation of protactinium and thorium by retention of thorium.

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

Extraction of gold, mercury, and lead with TEVA resin from HCl and HNO 3

The extraction behavior of 212 Pb, 197m Hg, and 194 Au on TEVA resin in HCl and HNO 3 solutions was studied with batch uptake, kinetics, and column studies. The uptake of mercury and gold was extremely high from HCl solutions, with maximum k’ >80,000 for both elements. The uptake of mercury was lower in HNO3 than HCl with a maximum k’ of ~ 8,000 in 0.02 M HNO 3 and decreasing uptake at higher concentrations of HNO3, which agrees well with previous work. The batch uptake of gold in HNO 3 was not measured, as it had been reported previously. The uptake of lead on TEVA resin in HCl was low with a maximum k’ of only ~ 90 in 1 M HCl. The uptake of lead in HNO 3 was negligible. The uptake kinetics of gold and mercury were characterized in HCl and HNO 3 solutions and high uptake was seen after ~ 60 s for both elements. Column separations of 212 Pb, 197m Hg, and 194 Au on TEVA resin from HCl and HNO 3 solutions are reported with high yields of mercury and lead, but with high losses of gold, which is retained on the resin. A rapid, high yield separation of 197m Hg from irradiated gold foils is presented with yields of ~ 100% for both elements and a total separation time of < 2 h.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗