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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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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Metallic Coating of Cerium Oxide Microspheres

The ability to remove heat is paramount to nuclear fuel performance and longevity. Retaining fission product and separating fuel from reactor coolant and the environment is also necessary to prevent radiological contamination. Conventional nuclear fuel for commercial light water reactors and radioisotope power systems (RPS) is composed of oxide powders pressed into a pellet (cm-scale) and then sealed into a metal cladding to confine the fuel. What typical fuels lack is a method to surround each particle of nuclear fuel in metal, thus providing a more intimate protection layer for accident tolerance and boosting the thermal extraction from the fuel element. In such a way, metal-coated fuel particles increase heat extraction efficiency over clad-pellet designs while increasing the accident tolerance of the fuel. Metal oxide microspheres have wide-ranging applications, including the realm of fuels for nuclear reactors and RPS. Microspheres of uranium oxide/uranium carbide, mixed uranium/plutonium oxides, transuranics, and thorium fuels have been extensively studied. Pacific Northwest National Laboratory has also demonstrated the production of 238 PuO 2 microspheres for RPS applications. Metal-coated oxide microsphere fuels may also be attractive for other applications such as nuclear thermal rockets, future nuclear reactor designs, and catalysts.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Solid-state syntheses and single-crystal characterizations of three tetravalent thorium and uranium silicates

Colorless crystals of ThSiO{sub 4} (huttonite) (1) and (Ca{sub 0.5}Na{sub 0.5}){sub 2}NaThSi{sub 8}O{sub 20} (2) have been synthesized by the solid-state reactions of ThO{sub 2}, CaSiO{sub 3}, and Na{sub 2}WO{sub 4} at 1073 K. Green crystals of (Ca{sub 0.5}Na{sub 0.5}){sub 2}NaUSi{sub 8}O{sub 20} (3) have been synthesized by the solid-state reactions of UO{sub 2}, CaSiO{sub 3}, and Na{sub 2}WO{sub 4} at 1003 K. All three compounds have been characterized by single-crystal X-ray diffraction. Compound 1 adopts a monazite-type three-dimensional condensed structure, which is built from edge- and corner-shared ThO{sub 9} polyhedra and SiO{sub 4} tetrahedra. Compounds 2 and 3 are isostructural and they crystallize in a steacyite-type structure. The structure consists of discrete pseudocubic [Si{sub 8}O{sub 20}]{sup 8−} polyanions, which are connected by An{sup 4+} cations into a three-dimensional framework. Each An atom coordinates to eight monodentate [Si{sub 8}O{sub 20}]{sup 8−} moieties in a square antiprismatic geometry. Na{sup +} and Ca{sup 2+} ions reside in the void within the framework. Raman spectra of 1, 2, and 3 were collected on single crystal samples. 1 displays more complex vibrational bands than thorite. Raman spectra of 2 and 3 are analogous with most of vibrational bands located at almost the same regions. - Graphical abstract: A Raman spectrum and crystal structures of (Ca{sub 0.5}Na{sub 0.5}){sub 2}NaAnSi{sub 8}O{sub 20} (An=Th, U), which contain pseudocubic [Si{sub 8}O{sub 20}]{sup 8−} polyanions and eight-coordinate An{sup 4+} cations. - Highlights: • Single crystal growth of three tetravalent actinide silicates from melts. • Single-crystal structures and Raman spectra of (Ca{sub 0.5}Na{sub 0.5}){sub 2}NaAnSi{sub 8}O{sub 20} (An=Th, U). • First report of Raman spectrum of huttonite on single crystal samples.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Analysis of Synergistic Fuel Cycle Options with Thorium and Heavy Water Reactors

Fuel cycle options (FCOs) with thorium-based fuels have characteristics that may have benefits for meeting certain objectives, such as transuranic actinide inventory management and overall natural resource utilization. Neutron irradiation of thorium and uranium-233 results in negligible production of transuranic actinides. This advantage is compromised, to a degree, when thorium fuels are used in conjunction with uranium-238; however, strategic reprocessing and fuel use (e.g., recycle of plutonium and/or minor actinides) can be used to manage this problem. Furthermore, thorium FCOs with reprocessing can extend the availability of natural nuclear resources by breeding new fissile material, recovering and recycling unused material, and achieving high burnups. In instances where natural thorium is more readily available than uranium, FCOs which use thorium may be preferable from sustainability and energy security perspectives. However, many hybrid uranium-thorium FCOs struggle to perform well in this regard, since large amounts of external fissile material (and therefore natural uranium) are required to breed the required uranium-233. DOE's evaluation and screening effort reports that for every metric ton (MT) of U-233 bred in a light water reactor for reuse, about 1000 MT of natural uranium are required to support such breeding, much of which is used inefficiently due to enrichment. The combination of HWRs and thorium-based fuels has the potential to reduce this consumption of natural uranium resources. Because heavy water moderates neutrons without significant absorption, fissile material requirements are lower compared to those of LWRs. This has enabled conventional 'once-through' HWRs to operate with only slightly-enriched or even natural uranium. Also, HWRs can be combined with LWRs in multistage FCOs where used LWR fuel can be processed and the remaining fissile content is sufficient to support use as fuel in HWRs in spite of the presence of neutron poisons (e.g., uranium-236); this concept has been demonstrated at a research scale in Korea. Thus, additional energy is extracted from the same initial natural uranium feed and uranium enrichment effort. Another consideration with using thorium-based fuels in HWRs is the current limited operational experience of the reactors and associated fuel cycle facilities using these fuels. However, work continues internationally towards gaining further experience. For example, at equilibrium the third stage of India's planned Three-Stage Nuclear Power Program uses thorium/uranium-233 or thorium/plutonium fuels with a fissile supply from second-stage fast reactors. Further, China plans to experiment with low-enriched uranium (LEU)-Th CANFLEX fuel bundles in a once-through configuration in its HWRs and a long-term objective is to transition to thorium use in a closed HWR FCO. Vanderbilt University (VU) and Oak Ridge National Laboratory (ORNL) are characterizing multi-stage, thermal-reactor FCOs that incorporate thorium and examining their potential performance. This paper presents insights from the examination of FCOs which consider the synergy of HWRs and thorium. Two multi-stage FCOs which incorporate thorium-based fuels in HWRs have been examined for their potential, one which uses recycled PWR uranium oxide fuel in conjunction with thorium in an HWR, and another that uses recycled HWR fuel in an MSR which also includes thorium. Both of the systems studied offer resource utilization improvements as compared to a once-through LWR fueled with low-enrichment uranium and highlight the potential synergy of thorium and HWRs. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Neutron Coincidence Measurements of Uranium-233 Oxide

Renewed international interest in thorium-fueled advanced reactors has challenged the safeguards community to address future proliferation concerns. Thorium-based technology presents many benefits but does not eliminate the proliferation risks associated with producing and processing fissile material. A byproduct of thorium-fueled reactors is uranium-233, which is classified as a direct-use material. As a result, the development of new or improved methods to characterize and measure materials containing 233U must mirror the pace of development of reactors and facilities that produce such material. Research is underway to assess, develop, and test approaches for safeguarding nuclear materials within the thorium fuel cycle. Neutron signatures from the nondestructive assay (NDA) of materials containing 233U are being quantified to inform the potential characterization of these materials. Using a traditional neutron coincidence counter and a series of well-documented 233U oxide samples, initial measurements have been made to assess the feasibility of 233U characterization and discrimination from other uranium isotopes, primarily 235U, using a combination of measurement techniques and analysis methods. Data acquisition is performed in list mode, allowing for a variety of analyses to be performed on the raw data that is not available using traditional shift register technology. Measurements were performed in passive and active configurations to quantify the strength of signal and to validate simulations in support of this work. This paper presents and discusses the results of the initial measurements of 233U oxide performed at Oak Ridge National Laboratory.

Lockhart, Madeline↗
DOE OSTI2014

Interaction of Ce{sub 1−x}Er{sub x}O{sub 2−y} nanoparticles with SiO{sub 2}-effect of temperature and atmosphere

Morphology, microstructure and phase evolution of homogeneous, nanocrystalline Ce{sub 1−x}Er{sub x}O{sub 2−x/2} mixed oxide (x=0.3 and 0.5), prepared by microemulsion method, supported on amorphous SiO{sub 2} was studied in oxidizing and reducing atmosphere by XRD, TEM, SEM-EDS and N{sub 2} adsorption. The system is structurally and chemically stable in the oxidizing atmosphere up to 1000 °C, exhibiting only a small increase of the mean crystallite size of the oxide to ∼4 nm. At 1100 °C formation of Er silicate with unusual structure isomorphic with y-Y{sub 2}Si{sub 2}O{sub 7} (yttrialite), stabilized by Ce{sup 4+} ions was observed. In the reducing atmosphere the Ce{sub 1−x}Er{sub x}O{sub 2−x/2} reacted with SiO{sub 2} already at 900 °C, due to high affinity of the reduced Ce{sup 3+} to form a silicate phase. At higher temperature the silicate crystallized into the tetragonal, low temperature A-(Ce{sub 1−x}Er{sub x}){sub 2}Si{sub 2}O{sub 7} polymorph. Such systems, containing nanocrystalline silicate particles with Er{sup 3+} ions placed in well defined sites embedded in silica matrix, may be interesting as highly efficient active components of optical waveguides amplifiers integrated with Si microelectronics. The nanocrystalline Ce–Er–O/SiO{sub 2} system prepared by the impregnation of the silica with the aqueous solution of nitrates appeared to be chemically inhomogeneous and less stable in both oxidising and reducing atmosphere. - Graphical abstract: Structure evolution of Ce{sub 0.5}Er{sub 0.5}O{sub 1.75} in air and in H{sub 2}. Display Omitted - Highlights: • Homogeneous 3 nm Ce{sub 1−x}Er{sub x}O{sub 2−y} particles were prepared and uniformly dispersed on SiO{sub 2}. • Er diffusion to SiO{sub 2} determines the stability of the mixed oxide in air to ∼1000 °C. • Spreading of Ce{sub 1−x}Er{sub x}O{sub 2−y} onto SiO{sub 2} occurs in hydrogen at 900 °C. • Nanocrystalline A-(Ce,Er){sub 2}Si{sub 2}O{sub 7} silicate forms in H{sub 2} at 1100 °C.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Combustion-assisted ink-jet printing of nuclear targets

Advances in target fabrication are critical to high-precision measurements in nuclear physics. This work details the preparation of patterned CeO 2 and ThO 2 architectures and thin-film targets via ink-jet deposition of combustible solutions. The produced targets were characterized by scanning electron microscopy (SEM), and by alpha-particle spectroscopy for radioactive targets to determine densities. Ink jet printing of the targets, used both ethanol and 2-methoxyethanol as solvents, with cerium or thorium nitrate as the oxidizer and acetylacetone as the fuel. Additionally, we found that the distance between each droplet dispersion (step size) played the most significant role in determining the final pattern uniformity and thickness. A 50 μm step size leads to relatively thick targets with a density of 350 μg/cm 2 . Significant overlap in droplet sizes leads to a heterogeneous target with an undesirable cracked surface structure. In contrast, 150 μm spacing yields thinner (20 μg/cm 2 ) patterned structures with excellent surface coverage. This method of Ink-jet printing provides a straightforward, scalable, and high-efficiency pathway to prepare custom made, high-quality targets for nuclear physics experiments.

CeO2↗
DOE OSTI2013

Experimentally characterizing the electronic structures of f-electron systems using advanced high resolution Fourier transform microwave spectroscopies

We aim to (i) provide data that directly addresses the fundamental roles of actinide valence electrons in chemical bonding, and (ii) serve to provide prototypical data for the heavy element computational chemistry community. These goals will be achieved through the first pure rotational spectroscopic measurements on prototypical systems at ultra-high resolution. These systems encompass low oxidation state uranium and thorium compounds including, but not limited to, UX and ThX, X = F, Cl, Br, I, and UY and ThY, Y = O, S, and other simple U and Th-containing compounds. Our primary experimental tools involve time-domain rotational spectroscopy achieving line widths and resolutions of a few kHz.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Accident tolerant, non-oxidizable MOX fuel fabrication

Thorium dioxide (ThO{sub 2}) has a set of physical-chemical properties that make it well suited to serve as a nuclear fuel matrix: it has a very high melting point, it cannot be further oxidized, it has low leachability in water, reasonable thermal conductivity (better than UO{sub 2}), and of course it is fertile. Collectively, these properties allow for a fuel ceramic with increased in / out of core stability. As such, Thor Energy and a consortium of entities that include Westinghouse, KAERI, Fortum, NNL, ITU and IFE have recently fabricated (Th,Pu)O{sub 2} pellet specimens in Norway. The Th-MOX production methodology was developed over the course of 2 years of ceramic production trials involving Ce-Th oxide mixtures. It was understood that parameters developed for CeO{sub 2} material might need to have been modified if trial results with PuO{sub 2} led to sub-optimal pellets. Among observations made in this work, the most important production parameter was the preparation of constituent / mixed powders. Correct powder morphology was key to achieving high fuel densities. The process parameters developed for (Th,Ce)O{sub 2} pellets were adopted with the expectation that these would serve as a sound basis for obtaining dense, homogeneous (Th,Pu)O{sub 2} fuel ceramic. The Th-MOX fuel manufacture campaign was successful in producing enough (Th,Pu)O{sub 2} pellets to assemble two 30 cm long fuel pins for testing in the Halden test reactor. These fuel rods will be fitted with various instruments to enable temperature, fission gas release and dimensional changes to be measured while operating at power in conditions similar to those of a BWR.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Oxidation State of 229 Th Recoils Implanted into MgF 2 Crystals

A solid-state nuclear clock based on the low-lying isomeric state in 229 Th has attracted growing interest. One potential problem for the solid-state nuclear clock approach is the suitability of the doped environment for photon emission of the nuclear isomeric state. Specifically, Th n+ n < 4 ions could open non-radiative decay routes for deexcitation, hindering the photon emission. Here we have used time-resolved photoluminescence (TRPL) and density functional theory (DFT) calculations to characterize MgF 2 crystals that have been implanted with 229 Th recoils via a-decay from a 233 U source with the goal of determining the charge state of the implanted thorium atoms. The DFT calculations predicted Th4+ to be the lowest energy oxidation state with Th3+ the next lowest in the MgF2 crystal environment. The DFT calculations also show Th4+:MgF 2 system has a band gap large enough so that the internal electron conversion decay channel is suppressed. Experimentally, we found no evidence for thorium in oxidations state other than +4 using TRPL spectroscopy that has a detection limit for Thn+ n < 4 ions several orders of magnitude smaller than the number of implanted 229Th recoils. This work shows that the solid-state approach is a viable option for a nuclear clock.

229Th Isomeric State↗
DOE OSTI2016

Thermodynamic calculations of oxygen self-diffusion in mixed-oxide nuclear fuels

Mixed-oxide fuels containing uranium with thorium and/or plutonium may play an important part in future nuclear fuel cycles. There are, however, significantly less data available for these materials than conventional uranium dioxide fuel. In the present study, we employ molecular dynamics calculations to simulate the elastic properties and thermal expansivity of a range of mixed oxide compositions. These are then used to support equations of state and oxygen self-diffusion models to provide a self-consistent prediction of the behaviour of these mixed oxide fuels at arbitrary compositions.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2013

The Use of Thorium within the Nuclear Power Industry - 13472

Thorium is 3 to 4 times more abundant than uranium and is widely distributed in nature as an easily exploitable resource in many countries. Unlike natural uranium, which contains ∼0.7% fissile {sup 235}U isotope, natural thorium does not contain any fissile material and is made up of the fertile {sup 232}Th isotope only. Therefore thorium and thorium-based fuel as metal, oxide or carbide, has been utilized in combination with fissile {sup 235}U or {sup 239}Pu in nuclear research and power reactors for conversion to fissile {sup 233}U, thereby enlarging fissile material resources. During the pioneering years of nuclear energy, from the mid 1950's to mid 1970's, there was considerable interest worldwide to develop thorium fuels and fuel cycles in order to supplement uranium reserves. Thorium fuels and fuel cycles are particularly relevant to countries having large thorium deposits but very limited uranium reserves for their long term nuclear power programme. The feasibility of thorium utilization in high temperature gas cooled reactors (HTGR), light water reactors (LWR), pressurized heavy water reactors (PHWRs), liquid metal cooled fast breeder reactors (LMFBR) and molten salt breeder reactors (MSBR) were demonstrated. The initial enthusiasm for thorium fuels and fuel cycles was not sustained among the developing countries later, due to new discovery of uranium deposits and their improved availability. However, in recent times, the need for proliferation-resistance, longer fuel cycles, higher burnup, and improved waste form characteristics, reduction of plutonium inventories and in situ use of bred-in fissile material has led to renewed interest in thorium-based fuels and fuel cycles. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2012

Solid state reactions of nanocrystalline Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75} mixed oxide with high surface area silica in oxidizing and reducing atmosphere

The interaction of nanocrystalline Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75} mixed oxide with a high surface amorphous silica support in an oxidizing and reducing atmosphere was studied by XRD, HRTEM, SAED, SEM and BET techniques. The Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75}-SiO{sub 2} system shows very high structural and size stability in the oxidizing atmosphere up to 1000 Degree-Sign C, but in hydrogen spreading of the oxide onto silica occurs at temperatures above 800 Degree-Sign C. In the oxidizing atmosphere stability of the mixed oxide is limited by extraction of ytterbium from the oxide driven by a tendency to form ytterbium silicates. A new polymorph of Yb silicate, isomorphic with y-Y{sub 2}Si{sub 2}O{sub 7} (yttrialite), has been identified in the samples containing the mixed Ce-Yb oxide. The absence of y-Yb{sub 2}Si{sub 2}O{sub 7} silicate in the Yb{sub 2}O{sub 3}-SiO{sub 2} samples treated in similar conditions indicates that Ce{sup 4+} ions are needed to stabilize the structure. - Graphical abstract: Structure evolution of nano-Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75}-SiO{sub 2} in air and in H{sub 2}. Highlights: Black-Right-Pointing-Pointer Nano-Ce{sub 0.50}Yb{sub 0.50}O{sub 1.75} on SiO{sub 2} is stable in air up to 1000 Degree-Sign C but spreads in hydrogen at 800 Degree-Sign C. Black-Right-Pointing-Pointer Formation of Yb silicates determines the stability of Ce{sub 0.50}Yb{sub 0.50}O{sub 1.75} at high temperatures. Black-Right-Pointing-Pointer New, y-Yb{sub 2}Si{sub 2}O{sub 7} silicate (yttrialite type) forms in Ce{sub 0.5}Yb{sub 0.5}O{sub 1.75}-SiO{sub 2} in H{sub 2} at 1100 Degree-Sign C.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Renewability and sustainability aspects of nuclear energy

Renewability and sustainability aspects of nuclear energy have been presented on the basis of two different technologies: (1) Conventional nuclear technology; CANDU reactors. (2) Emerging nuclear technology; fusion/fission (hybrid) reactors. Reactor grade (RG) plutonium, {sup 233}U fuels and heavy water moderator have given a good combination with respect to neutron economy so that mixed fuel made of (ThO{sub 2}/RG‐PuO{sub 2}) or (ThC/RG-PuC) has lead to very high burn up grades. Five different mixed fuel have been selected for CANDU reactors composed of 4 % RG‐PuO{sub 2} + 96 % ThO{sub 2}; 6 % RG‐PuO{sub 2} + 94 % ThO{sub 2}; 10 % RG‐PuO{sub 2} + 90 % ThO{sub 2}; 20 % RG‐PuO{sub 2} + 80 % ThO{sub 2}; 30 % RG‐PuO{sub 2} + 70 % ThO{sub 2}, uniformly taken in each fuel rod in a fuel channel. Corresponding operation lifetimes have been found as ∼ 0.65, 1.1, 1.9, 3.5, and 4.8 years and with burn ups of ∼ 30 000, 60 000, 100 000, 200 000 and 290 000 MW.d/ton, respectively. Increase of RG‐PuO{sub 2} fraction in radial direction for the purpose of power flattening in the CANDU fuel bundle has driven the burn up grade to 580 000 MW.d/ton level. A laser fusion driver power of 500 MW{sub th} has been investigated to burn the minor actinides (MA) out of the nuclear waste of LWRs. MA have been homogenously dispersed as carbide fuel in form of TRISO particles with volume fractions of 0, 2, 3, 4 and 5 % in the Flibe coolant zone in the blanket surrounding the fusion chamber. Tritium breeding for a continuous operation of the fusion reactor is calculated as TBR = 1.134, 1.286, 1.387, 1.52 and 1.67, respectively. Fission reactions in the MA fuel under high energetic fusion neutrons have lead to the multiplication of the fusion energy by a factor of M = 3.3, 4.6, 6.15 and 8.1 with 2, 3, 4 and 5 % TRISO volume fraction at start up, respectively. Alternatively with thorium, the same fusion driver would produce ∼160 kg {sup 233}U per year in addition to fission energy production in situ, multiplying the fusion energy by a factor of ∼1.3.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2015

Breeding of {sup 233}U in the thorium–uranium fuel cycle in VVER reactors using heavy water

A method is proposed for achieving optimal neutron kinetics and efficient isotope transmutation in the {sup 233}U–{sup 232}Th oxide fuel of water-moderated reactors with variable water composition (D{sub 2}O, H{sub 2}O) that ensures breeding of the {sup 233}U and {sup 235}U isotopes. The method is comparatively simple to implement.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Alternative Energy: Production of H{sub 2} by Radiolysis of Water in the Rocky Cores of Icy Bodies

We applied a model of radiolysis in earthly rock–water mixtures to several known or suspected ocean worlds: Enceladus, Ceres, Europa, Titania, Oberon, Pluto, and Charon. In this model, radiation emitted by the long-lived radionuclides ({sup 40}K, {sup 232}Th, {sup 235}U, and {sup 238}U) contained in the ordinary chondrite-like rocks is partly absorbed by the water permeating the material of each body’s core. The physical and chemical processes that follow release molecular hydrogen (H{sub 2}), which is a molecule of astrobiological interest. We compared the calculated production of H{sub 2} by radiolysis in each body’s core to published estimates of production by serpentinization. This study presents production calculations over 4.5 Gyr for several values of rock porosity. We found that radiolysis can produce H{sub 2} quantities equivalent to a few percent of what is estimated from serpentinization. Higher porosity, which is unlikely at the scale of a body’s entire core but possible just under the seafloor, can increase radiolytic production by almost an order of magnitude. The products of water radiolysis also include several oxidants, allowing for production of life-sustaining sulfates. Though previously unrecognized in this capacity, radiolysis in an ocean world’s outer core could be a fundamental agent in generating the chemical energy that could support life.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

New NDA Methods for Thorium Fuel Cycle Safeguards (Mid-Project Report)

This project is developing new Non-Destructive Assay (NDA) safeguards techniques for emergent thorium fuel cycles based on Neutron Resonance Transmission Analysis (NRTA), which can assay 233 U and 235 U when they are present together in a sample with potentially high gamma-ray backgrounds from fission products and 232 U. Existing passive techniques face large challenges for this task so new active interrogation methods are needed. This effort is also exploring how gamma-ray signatures can complement NRTA for enhanced assayed performance. This project leverages an NRTA system being developed at PNNL in collaboration with MIT, which uses a commercially available deuterium-tritium neutron generator at short standoff (~2 m). We aim to assess the feasibility and performance of these new NDA techniques for the range of relevant samples in thorium fuel cycles. Key advancements described in this mid-project report include NRTA system design for thorium safeguards measurements, characterization of 233 U oxide powder at PNNL, a survey of detector technologies suitable for NRTA in high gamma background environments, successful preliminary demonstration of a quantitative isotopic estimation algorithm, and first NRTA measurements of a thorium sample.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Theoretical analysis of uranium-doped thorium dioxide: Introduction of a thoria force field with explicit polarization

Thorium dioxide is used industrially in high temperature applications, but more insight is needed into the behavior of the material as part of a mixed-oxide (MOX) nuclear fuel, incorporating uranium. We have developed a new interatomic potential model including polarizability via a shell model, and commensurate with a prominent existing UO{sub 2} potential, to conduct configurational analyses and to investigate the thermophysical properties of uranium-doped ThO{sub 2}. Using the GULP and Site Occupancy Disorder (SOD) computational codes, we have analyzed the distribution of low concentrations of uranium in the bulk material, where we have not observed the formation of uranium clusters or the dominance of a single preferred configuration. We have calculated thermophysical properties of pure thorium dioxide and Th{sub (1−x)}U{sub x}O{sub 2} which generated values in very good agreement with experimental data.

36 MATERIALS SCIENCE↗