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Zircon (U-Th)/He Impact Crater Thermochronometry and the Effects of Shock Microstructures on Helium Diffusion Kinetics

Absolute age determination of impact cratering events remains difficult and often controversial; a challenge that has resulted in < 50% of known impact craters regarded as accurately and precisely dated. Besides conventional 40Ar/39Ar and U-Pb methods, zircon (U-Th)/He (ZHe) dating of impactites has been applied to large- to medium-sized impact structures. ZHe dates can be fully reset in minutes at 1000°C, which is commonly reached in central sections of the melt sheet, whereas resetting of ZHe at <300°C, which might be encountered near the crater margins or persist in post-impact hydrothermal systems, may take >103-6 years. There is a critical need to quantify the effects of shock-induced microstructures and impact metamorphism on helium diffusion kinetics in well-characterized, variably shocked zircon to further establish the reliability of (U-Th)/He for dating impacts. For this purpose, we investigated suevite and impact melt samples from two impact structures, the Chicxulub multi-ring basin and the Ries complex crater, which enables us to compare zircon helium diffusion kinetics from impact structures with differing sizes, ages, and hydrothermal system longevities. Shock microstructures were characterized by backscattered-electron (BSE) imaging prior to diffusion step-heating fractional release experiments using light-bulb furnace with prograde and retrograde incremental 10°C steps from 250°C to 600°C. Afterward, we characterize the diffusion domain sizes and their interconnectivity within the shocked zircon grains using electron backscatter diffraction (EBSD). We find that zircon with few shock microstructures exhibit no significant deviation from helium diffusion kinetics of undamaged zircon. In contrast, zircon grains with planar deformation features (PDFs) and granular textures classified by BSE and EBSD are characterized by a dramatic decrease in helium retentivity, similar to radiation damaged grains, due to a reduction in the effective domain size and the introduction of interconnected fast diffusion pathways created by shock microstructures. A subset of grains were dated by ZHe after the external morphology of the grains was determined by BSE imaging. The euhedral grains yielded a weighted mean age within the uncertainty of the accepted impact ages, whereas the grains with PDFs or granular textures exhibited younger ages. Thus, these diffusion experiments and ZHe dates suggest that the dramatic decrease in domain size likely renders shocked grains more susceptible to impact-induced hydrothermal resetting and subsequent overprinting. Hence, characterization of shock microstructures is critical for determining accurate impact ages using ZHe methods especially when applied to previously unconstrained craters. The thermochronometer also offers the opportunity to determine the magnitude and duration of post-impact hydrothermal circulation.

zircon↗
DOE OSTI2022

Why Lady Godiva Should be Replaced as the Default Validation Experiment for U-235 Nuclear Data

For the past seven decades the Lady Godiva benchmark (HEU-MET-FAST-001) has been the primary experiment used for 235 U nuclear data validation. The papers associated with large nuclear data library releases such as ENDF/B-VII.1 and ENDF/B-VIII.0 refer to it frequently. The reasons why HEU-MET-FAST-001 has been used as the primary validation experiment for 235 U nuclear data validation will be discussed in the following section. However, as discussed among the benchmark community, the standards associated with International Criticality Safety Benchmark Evaluation Project (ICSBEP) evaluations have changed throughout time; this is subject of the OECD/NEA WPEC (Working Party on Nuclear Criticality Safety) Subgroup 8. HEU-MET-FAST-001 is an older benchmark (issued during the inaugural year of ICSBEP in 1996 with only minor revisions occurring since then) and (along with many of the other benchmarks from this era) does not meet the standards for a modern benchmark. This work explores why HEU-MET-FAST-001 is useful for 235 U nuclear data validation and discusses other alternative validation experiments.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2020

The Impact of Ethylenediaminetetraacetic Acid (EDTA) on the Sorption of Nd(III), Th{sup (IV)}, and U(VI) onto Dolomite in WIPP-Relevant Brines, GWB and ERDA-6 - 20356

Storage of legacy, transuranic waste at the Waste Isolation Pilot Plant (WIPP) requires accurate risk models for performance assessments. These models must predict the long-term fate and transport of contaminants in the WIPP and surrounding environment. Laboratory support is necessary for the development of an accurate model through better understanding of contaminant behavior in the WIPP. The WIPP is a deep geologic repository that is characterized by high ionic strength due to evaporite deposits in the Salado formation (porewaters up to 7.4 M). High concentrations of sodium chloride (NaCl), calcium chloride (CaCl{sub 2}), and magnesium chloride (MgCl{sub 2}) are particularly of concern due to their potential impact on solubility and ultimately transport of contaminants of concern. Additionally, ligands capable of forming strong complexes with metals are found in significant concentrations in the WIPP environment due to their disposal from waste processing and formation during degradation of repository components (e.g. cellulose degradation by calcium hydroxide in cement). Consequently, there is a need to investigate the fate and transport of contaminants in the WIPP environment with a focus on the effects of high ionic strength and strongly coordinating ligands. Contaminants of high concern include the actinides (U(VI), Pu(IV), and Am(III)). Laboratory support of the WIPP modeling efforts was provided by this research. A series of batch experiments were utilized to study the impact of ionic strength, contaminant concentration, and the presence of ethylenediaminetetraacetic acid (EDTA) on the sorption of Nd(III), Th(IV), and U(VI) onto dolomite, a carbonate mineral found within the Culebra formation. The Culebra formation is the most transmissive layer above the WIPP, making transport of contaminants the most likely route in previous risk assessments. Two brines specifically designed to imitate conditions within the WIPP environment were used in these experiments. The U.S. Energy Research and Development Administration Well 6 (ERDA-6, 95%) brine simulates a low Mg environment, while the generic weep brine (GWB, 95%) simulates the WIPP environment with a high Mg concentration. Mg is added to the repository in the form of MgO as an engineered barrier and is naturally present in some formations. It is expected to scavenge carbonate from solutions decreasing formation of the highly soluble and competitive uranium-carbonate complexes. EDTA is used during manipulations of nuclear materials due to its ability to form strong, stable complexes with the actinides and may be found in high concentrations (up to 0.08 mM) within the WIPP as waste canisters degrade. Further, it may provide additional avenues for unwanted transport of contaminants. Nd(III) and Th(IV) were used as stable analogues of Am(III) and Pu(IV), respectively, to represent the most common oxidation states of actinides in the WIPP environment in addition to U(VI). The potential for colloid formation was also investigated with low and high concentrations of contaminants (10 and 1000 μg/L) using three size-dependent particle separation steps. The results of this research provide a better understanding of potential behavior of actinides in the presence of EDTA and within WIPP-relevant brines. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Whole core analysis of OECD/NEA TVA-WB1 benchmark exercise 1 using continuous-energy Monte Carlo code MVP with JENDL-4.0u and ENDF/B-VII.0

The TVA WB1 benchmark problem was precisely modeled in accordance with the geometry and material specifications, and benchmark exercise 1 was solved with the MVP code and the nuclear data libraries based on JENDL-4.0u (JENDL-4.0 updated file) and ENDF/B-VII.0. The criticality, the control rod bank worth, the isothermal temperature coefficient (ITC), the integral rod worth of bank D, and differential soluble boron worth (DBW) were obtained. The criticality and the control rod bank worth were compared with the measured data and published calculation results with other codes, Serpent and KENO. The criticality and the control rod bank worth calculated by MVP and the libraries agree with the measured and the published calculation results within the criteria specified in the ANSI/ANS standard. From these results, the calculation model for the MVP and the libraries was verified. The other parameters such as ITC, the integral rod worth, and DBW were also compared between JENDL-4.0u and ENDF/B-VII.0. The comparison of the results shows JENDL-4.0u and ENDF/B-VII.0 give comparable results within the standard deviation, the difference between libraries is small. (author)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2025

Status of the n+ 234 U evaluation in the resolved resonance region (*), (**)

In natural uranium, the 234 U isotope represents only 0.0055%, however, this minor isotope can affect highly enriched uranium metal benchmark calculations. In fact, enriched uranium contains more 234 U than natural uranium as the result of the uranium enrichment process. Therefore, the n+ 234 U nuclear data evaluation is one of the milestones of the APPENDIX B within the Nuclear Criticality Safety Program (NCSP).

AMPX↗
DOE OSTI2020

Modeling plasma toroidal flow profile control via NTV torque with n = 2 3D fields in MAST-U

Toroidal modeling utilizing the MARS-Q code shows that large (compared to electromagnetic torque) neoclassical toroidal viscous (NTV) torque can be achieved in the plasma core region in reference MAST(-U) L-mode plasmas, by applying the n=2 (n is the toroidal mode number) 3-D fields generated by the magnetic coils used for controlling the edge localized mode and/or by the error field correction coils. Large NTV torque, occurring at relatively slow plasma flow, in combination with strong variation of the torque amplitude versus the coil phasing of the 3-D coils, offers a tool to control the plasma toroidal rotation profile in spherical tokamaks. To effectively employ the toroidal NTV torque, the potentially fast initial flow needs to first be damped by 3-D fields. In conclusion, MARS-Q quasi-linear initial value simulations demonstrate that this is achievable in MAST-U, within the designed 3-D coil current capability for the device.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Mechanical Properties of Irradiated U-10 wt. %Mo Alloy Degraded by Porosity Development

In this study, a plate-type nuclear fuel consisting of a solid monolithic foil of U-10 wt. %Mo is under development for use in the United States' high-performance research reactors. In support of developing this fuel, the fuel has been fabricated for the first time by a commercial fuel vendor and subsequently irradiated in a test reactor. This provides an opportunity to evaluate postirradiation mechanical properties of the commercially fabricated fuel. Four-point bend testing was conducted on the irradiated U-10Mo samples to generate the fuel material properties, including the modulus of elasticity and the bending strength. Although the material behaves in a brittle manner due to the accumulated porosity, a general trend of strength and modulus reduction was found as fission density increases. The data produced was evaluated using both Weibull statistics and a modulus degradation model with recommendations provided.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Materials Data on U(RhO3)2 by Materials Project

U(RhO3)2 is Hydrophilite-derived structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. U6+ is bonded to six O2- atoms to form UO6 octahedra that share corners with eight equivalent RhO6 octahedra and edges with two equivalent RhO6 octahedra. The corner-sharing octahedra tilt angles range from 48–51°. There are four shorter (2.09 Å) and two longer (2.13 Å) U–O bond lengths. Rh3+ is bonded to six O2- atoms to form RhO6 octahedra that share corners with four equivalent UO6 octahedra, corners with four equivalent RhO6 octahedra, an edgeedge with one UO6 octahedra, and an edgeedge with one RhO6 octahedra. The corner-sharing octahedra tilt angles range from 48–51°. There are a spread of Rh–O bond distances ranging from 2.04–2.06 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one U6+ and two equivalent Rh3+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to one U6+ and two equivalent Rh3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(BRu)4 by Materials Project

U(RuB)4 crystallizes in the tetragonal I4_1/acd space group. The structure is three-dimensional. U4+ is bonded in a 12-coordinate geometry to twelve equivalent B3- atoms. There are a spread of U–B bond distances ranging from 2.96–3.22 Å. Ru2+ is bonded to five equivalent B3- atoms to form a mixture of distorted edge and corner-sharing RuB5 trigonal bipyramids. There are a spread of Ru–B bond distances ranging from 2.14–2.26 Å. B3- is bonded in a 6-coordinate geometry to three equivalent U4+, five equivalent Ru2+, and one B3- atom. The B–B bond length is 1.75 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(CoP)2 by Materials Project

UCo2P2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. U3+ is bonded in a 4-coordinate geometry to four equivalent Co+1.50+ and nine P3- atoms. All U–Co bond lengths are 2.78 Å. There are a spread of U–P bond distances ranging from 3.15–3.34 Å. There are two inequivalent Co+1.50+ sites. In the first Co+1.50+ site, Co+1.50+ is bonded in a single-bond geometry to one P3- atom. The Co–P bond length is 2.07 Å. In the second Co+1.50+ site, Co+1.50+ is bonded in a 4-coordinate geometry to four equivalent U3+ atoms. There are two inequivalent P3- sites. In the first P3- site, P3- is bonded in a 8-coordinate geometry to four equivalent U3+ and four equivalent P3- atoms. All P–P bond lengths are 2.26 Å. In the second P3- site, P3- is bonded in a distorted single-bond geometry to five equivalent U3+, one Co+1.50+, and four equivalent P3- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(Mo3S4)2 by Materials Project

U(Mo3S4)2 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. U4+ is bonded in a body-centered cubic geometry to eight S2- atoms. There are two shorter (2.74 Å) and six longer (2.94 Å) U–S bond lengths. Mo2+ is bonded to five S2- atoms to form a mixture of edge and corner-sharing MoS5 trigonal bipyramids. There are a spread of Mo–S bond distances ranging from 2.42–2.59 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 4-coordinate geometry to one U4+ and three equivalent Mo2+ atoms. In the second S2- site, S2- is bonded in a 5-coordinate geometry to one U4+ and four equivalent Mo2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(BH4)4 by Materials Project

U(BH4)4 crystallizes in the tetragonal P4_32_12 space group. The structure is three-dimensional. U4+ is bonded in a 10-coordinate geometry to fourteen H+0.50+ atoms. There are a spread of U–H bond distances ranging from 2.26–2.45 Å. There are two inequivalent B3- sites. In the first B3- site, B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There is one shorter (1.23 Å) and three longer (1.24 Å) B–H bond length. In the second B3- site, B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There is one shorter (1.20 Å) and three longer (1.25 Å) B–H bond length. There are eight inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to one U4+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to one U4+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to one U4+ and one B3- atom. In the fourth H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to one U4+ and one B3- atom. In the fifth H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to one U4+ and one B3- atom. In the sixth H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to one B3- atom. In the seventh H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to one U4+ and one B3- atom. In the eighth H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to one U4+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(OF)2 by Materials Project

UO2F2 crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three UO2F2 sheets oriented in the (0, 0, 1) direction. U6+ is bonded to two equivalent O2- and six equivalent F1- atoms to form distorted edge-sharing UO2F6 hexagonal bipyramids. Both U–O bond lengths are 1.78 Å. All U–F bond lengths are 2.45 Å. O2- is bonded in a single-bond geometry to one U6+ atom. F1- is bonded in a trigonal planar geometry to three equivalent U6+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(IO4)2 by Materials Project

U(O4I)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. U6+ is bonded to eight O2- atoms to form distorted edge-sharing UO8 hexagonal bipyramids. There are a spread of U–O bond distances ranging from 1.82–2.51 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one U6+ and one I5+ atom. The O–I bond length is 2.79 Å. In the second O2- site, O2- is bonded in a 1-coordinate geometry to one U6+ and two equivalent I5+ atoms. There are one shorter (1.86 Å) and one longer (2.55 Å) O–I bond lengths. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent U6+ and one I5+ atom. The O–I bond length is 1.89 Å. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent I5+ atoms. There are one shorter (1.81 Å) and one longer (2.48 Å) O–I bond lengths. I5+ is bonded in a 6-coordinate geometry to six O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(CoB)4 by Materials Project

U(CoB)4 crystallizes in the tetragonal P4_2/nmc space group. The structure is three-dimensional. U4+ is bonded in a 12-coordinate geometry to twelve equivalent B3- atoms. There are eight shorter (2.86 Å) and four longer (2.91 Å) U–B bond lengths. Co2+ is bonded in a 5-coordinate geometry to five equivalent B3- atoms. There are four shorter (2.07 Å) and one longer (2.10 Å) Co–B bond lengths. B3- is bonded in a 6-coordinate geometry to three equivalent U4+, five equivalent Co2+, and one B3- atom. The B–B bond length is 1.74 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(CrSi)2 by Materials Project

U(CrSi)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. U3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All U–Si bond lengths are 3.02 Å. Cr+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of corner and edge-sharing CrSi4 tetrahedra. All Cr–Si bond lengths are 2.39 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent U3+, four equivalent Cr+2.50+, and one Si4- atom. The Si–Si bond length is 2.38 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(TeO3)3 by Materials Project

UTe3O9 crystallizes in the cubic Pa-3 space group. The structure is three-dimensional. there are two inequivalent U6+ sites. In the first U6+ site, U6+ is bonded in a distorted hexagonal bipyramidal geometry to eight O2- atoms. There are two shorter (1.82 Å) and six longer (2.50 Å) U–O bond lengths. In the second U6+ site, U6+ is bonded in a distorted hexagonal bipyramidal geometry to eight O2- atoms. There are two shorter (1.83 Å) and six longer (2.43 Å) U–O bond lengths. Te4+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Te–O bond distances ranging from 1.91–2.46 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one U6+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one U6+ and two equivalent Te4+ atoms. In the third O2- site, O2- is bonded in a single-bond geometry to one U6+ atom. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to one U6+ and two equivalent Te4+ atoms. In the fifth O2- site, O2- is bonded in a trigonal non-coplanar geometry to three equivalent Te4+ atoms.

36 MATERIALS SCIENCE↗