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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Challenging the thorium-immobility paradigm

Thorium is the most abundant actinide in the Earth’s crust and has universally been considered one of the most immobile elements in natural aqueous systems. This view, however, is based almost exclusively on solubility data obtained at low temperature and their theoretical extrapolation to elevated temperature. The occurrence of hydrothermal deposits with high concentrations of Th challenges the Th immobility paradigm and strongly suggests that Th may be mobilized by some aqueous fluids. Here, we demonstrate experimentally that Th, indeed, is highly mobile at temperatures between 175 and 250°C in sulfate-bearing aqueous fluids due to the formation of the highly stable Th(SO 4 ) 2 aqueous complex. The results of this study indicate that current models grossly underestimate the mobility of Th in hydrothermal fluids, and thus the behavior of Th in ore-forming systems and the nuclear fuel cycle needs to be re-evaluated.

58 GEOSCIENCES↗
DOE OSTI2024

Structural chemistry of penta- and hexanitrato thorium($\tiny{IV}$) complexes isolated using N–H donors

In this study, a series of fifteen tetravalent thorium phases were prepared. The compounds were isolated from acidic aqueous nitrate solutions using protonated nitrogen heterocycles of varying hydrogen-bond donation strength. Structural analysis via single crystal X-ray diffraction showed that the structures are built from pentanitrato, [Th(NO 3 ) 5 (H 2 O) 2 ] 1- , and hexanitrato, [Th(NO 3 ) 6 ] 2- , molecular units, with the latter being far more prevalent in the solid state. The vibrational properties of the compounds were examined using Raman and IR spectroscopy; the spectra are dominated by stretches characteristic of nitrate and the organic ions. The relative energetics of nitrate complexation was examined using electronic structure theory. These results confirmed that there are clear thermodynamic sinks for the penta- and hexanitrato structural units that were observed experimentally. Additionally, electrostatic surface potentials (ESPs) were calculated in an effort to better understand the counterion stabilization of the complexes. The ESP surfaces showed that the position of the water and nitrate molecules and the coordination geometry of the metal complex had a clear effect on the polarizability of the two structural motifs. Despite limited speciation of the Th–nitrate structural units, the compounds exhibit rich supramolecular chemistry resulting from hydrogen bonding of the Th complexes with the organic N–H donors and π–π stacking interactions from the protonated N-heterocycles.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The permanent electric dipole moment of thorium sulfide, ThS

Numerous rotational lines of the (18.26)1-X{sup 1}Σ{sup +} band system of thorium sulfide, ThS, were recorded near 547.6 nm at a resolution of approximately 30 MHz. Measurements were made under field-free conditions, and in the presence of a static electric field. The field-free spectrum was analyzed to produce rotational and Λ-doubling parameters. The Stark shifts induced by the electric field were analyzed to determine permanent electric dipole moments, μ{sup -vector}{sub el}, of 4.58(10) D and 6.72(5) D for the X{sup 1}Σ{sup +} (v = 0) and (18.26)1 states, respectively. The results are compared with the predictions of previous and new electronic structure calculations for ThS, and the properties of isovalent ThO.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Structural and mechanical properties of thorium carbide

We have investigated the cohesive energies, equilibrium lattice constants, pressure-volume relationship, phase transition pressure and elastic constant for thorium carbide using an interionic potential theory with modified ionic charge, which includes Coulomb screening effect due to d-electrons. This compound undergoes structural phase transition from NaCl (B{sub 1}) to CsCl (B{sub 2}) structure at high pressure 40 GPa. We have also calculated bulk, Young, and shear moduli, Poisson ratio and anisotropic ratio in NaCl (B{sub 1}) structure and compared them with other experimental and theoretical results which show a good agreement.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Assessment of radionuclides (uranium and thorium) atmospheric pollution around Manjung district, Perak using moss as bio-indicator

Bio-monitoring method using mosses have been widely done around the world and the effectiveness has been approved. Mosses can be used to assess the levels of atmospheric pollution as mosses pick up nutrients from the atmosphere and deposition retaining many trace elements. In this study, the deposition of two radionuclides; uranium (U) and thorium (Th) around Manjung districts have been evaluated using Leucobryum aduncum as bio-monitoring medium. The samples were collected from 24 sampling sites covering up to 40 km radius to the North, North-East and South-East directions from Teluk Rubiah. The concentrations of U and Th in moss samples were analysed using Energy Dispersive X-Ray Fluorescence (EDXRF) Spectrometer. The concentrations of Th are in the range of 0.07-2.09 mg/kg. Meanwhile, the concentrations of U in the moss are in the range of 0.03-0.18 mg/kg. The Enrichment Factor (EF) was calculated to determine the origin of the radionuclides distributions. Other than that, the distribution maps were developed to observe the distribution of the radionuclides around the study area.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Ab-initio calculations on melting of thorium

Ab-initio molecular dynamics study has been performed on face centered cubic structured thorium to determine its melting temperature at room pressure. The ion-electron interaction potential energy calculated as a function of temperature for three volumes (a{sub 0}){sup 3} and (1.02a{sub 0}){sup 3} and (1.04a{sub 0}){sup 3} increases gradually with temperature and undergoes a sharp jump at ~2200 K, ~2100 K and ~1800 K, respectively. Here, a{sub 0} = 5.043 Å is the equilibrium lattice parameter at 0 K obtained from ab-initio calculations. These jumps in interaction energy are treated as due to the onset of melting and corresponding temperatures as melting point. The melting point of 2100 K is close to the experimental value of 2023 K. Further, the same has been verified by plotting the atomic arrangement evolved at various temperatures and corresponding pair correlation functions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Defect-induced phonon-resonant scattering and its influence on thermal transport of irradiated thorium-dioxide

Thermal transport in proton irradiated thorium-dioxide (ThO 2 ) is investigated. Using a combination of experiments and first-principles computational framework, the role of lattice defects on thermal conductivity is analyzed. A resonant-phonon scattering mechanism beyond the traditionally considered Rayleigh scattering is found to significantly influence low-temperature thermal transport in the presence of irradiation-induced point defects. The existence of localized phonon modes associated with irradiation-induced defects is suggested by the inability of the first-principles based thermal conductivity model—which considers only three-phonon interactions and phonon-defects scattering using the Tamura formalism—to predict the experimental results, unless a resonant scattering mechanism is included. The emergence of additional peaks in the Raman spectra in the proximity of phonon-resonant frequency provides further evidence for the existence of localized modes. Coupled with a microstructure evolution model, this analysis enables more accurate analysis for contrasting the contributions of different phonon scattering mechanisms across all irradiation doses and temperatures.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Laser resonance ionization spectroscopy of thorium

High-lying Rydberg and autoionizing (AI) states of thorium (Th) have been studied via resonance laser ionization spectroscopy at both TRIUMF Canada’s particle accelerator center and Oak Ridge National Lab (ORNL). Multiple Rydberg series converging to the ionization potential (IP) were observed via different stepwise laser excitation schemes and were assigned to be the 6d 2 7s ( 4 F 3/2 ) np, nd, and nf series. Analysis of these series enabled the determination of the IP to be 50 868.735(54) cm −1 , which improved the precision by two orders of magnitude over the current adopted NIST value of 50 867(2) cm −1 . Additionally, four AI Rydberg series were identified and assigned to nf and nd series converging to the 6d 2 7s 4 F 5/2 and 6d7s 2 2 D 3/2 metastable states of Th + . In conclusion, the measured energies of the Rydberg and AI Rydberg states are reported, and observed perturbations within the series are discussed.

Rydberg series↗
DOE OSTI2010

Functional Sorbents for Selective Capture of Plutonium, Americium, Uranium, and Thorium in Blood

Nano-engineered solid sorbents for chelation of actinides (239Pu, 241Am, uranium, thorium) from human blood were developed and evaluated in vitro. These sorbents, known as the self-assembled monolayer on mesoporous supports (SAMMSTM), are hybrid materials created from attachment of organic moieties onto extremely high surface area mesoporous silica. The organic moieties known to be effective at capturing actinides including three isomers of hydroxypyridinone, diphosphonic acid, acetamide phosphonic acid, glycinyl urea, and diethylenetriamine pentaacetate analog were evaluated. SAMMS are being reported elsewhere as potential candidates for orally administered drug for radionuclide decorporation. Herein, actinide decorporation of SAMMS in blood were evaluated to assess their viability for sorbent hemoperfusion in renal insufficient patients, whose kidney clear radionuclides at very slow rate. Sorption affinity (Kd), sorption rate, selectivity, and stability of SAMMS were measured in batch contact experiments. An isomer of hydroxypyridinone (3,4-HOPO) on SAMMS demonstrated the highest affinity for decorporation of all four actinides and outperformed the DTPA analog on SAMMS and on commercial resins by a factor of 103-fold in term of affinity. A fifty percent reduction of actinides in blood was achieved within minutes with no evidence of protein fouling and material leaching in blood after 24 hr of contact time. Less than 0.4 wt.% of Si was dissolved from 3,4-HOPO-SAMMS across the pH of 0 to 8. The engineered form of SAMMS (bead format) was further evaluated in a 100-fold scaled-down hemoperfusion device and showed no blood clotting after 2 hr. A 0.2 g of SAMMS could reduce 50 wt.% of 100 ppb uranium in 50 mL of plasma in just 18 min and that of 500 dpm mL-1 in just 24 min. 3,4-HOPO-SAMMS has a long shelf-life in air and at room temperature for at least 8 years, indicating their feasibility for stockpiling in preparedness for emergency.

Actinide↗
DOE OSTI2017

Identifying Rare Earth Elements and Thorium and Uranium in Iron Oxide–Apatite Deposit of Gazestan Bafgh, Southeast of Iran

The Gazestan magnetite-apatite deposit is one of Kiruna-type deposits located 78 km from Bafgh in the province of Yazd, in the Bafgh Posht-e-Badam district, southeast of Iran. In the mining region of Bafgh, volcanic rocks and Precambrian volcano-sedimentary are the main host of iron-apatite deposits. Iron deposits are essentially located in Bafgh region inside the green acidic metamorphic rocks. Volcanic rocks are basically rhyolite and rhyodacitic and the sedimentary units are mostly made of dolomite. Rock units of the region belong to the Rizzo series. The Bafgh apatite compounds are fluoride-type and seen in the monazite mineral. The similarity of the rare earth elements pattern in all samples indicates the magma source. The most amount of rare earth elements in the Gazestan deposit include 7766.25 ppm and the most amount of Th is equal to 65.1 ppm and U is equal to 8.33 ppm. The most amount of P2O5 s equal to 26.5 wt% and Fe is equal to 61.3 wt%. Also, it can be concluded that due to their high correlation with rare earth elements, the deposit is of Uranium Thorium-bearing type.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Utilization of non-weapons-grade plutonium and highly enriched uranium with breeding of the {sup 233}U isotope in the VVER reactors using thorium and heavy water

A method for joint utilization of non-weapons-grade plutonium and highly enriched uranium in the thorium–uranium—plutonium oxide fuel of a water-moderated reactor with a varying water composition (D{sub 2}O, H{sub 2}O) is proposed. The method is characterized by efficient breeding of the {sup 233}U isotope and safe reactor operation and is comparatively simple to implement.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

On the equilibrium isotopic composition of the thorium–uranium–plutonium fuel cycle

The equilibrium isotopic compositions and the times to equilibrium in the process of thorium–uranium–plutonium oxide fuel recycling in VVER-type reactors using heavy water mixed with light water are estimated. It is demonstrated thEhfat such reactors have a capacity to operate with self-reproduction of active isotopes in the equilibrium mode.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2011

Study of a multi-beam accelerator driven thorium reactor

The primary advantages that accelerator driven systems have over critical reactors are: (1) Greater flexibility regarding the composition and placement of fissile, fertile, or fission product waste within the blanket surrounding the target, and (2) Potentially enhanced safety brought about by operating at a sufficiently low value of the multiplication factor to preclude reactivity induced events. The control of the power production can be achieved by vary the accelerator beam current. Furthermore, once the beam is shut off the system shuts down. The primary difference between the operation of an accelerator driven system and a critical system is the issue of beam interruptions of the accelerator. These beam interruptions impose thermo-mechanical loads on the fuel and mechanical components not found in critical systems. Studies have been performed to estimate an acceptable number of trips, and the value is significantly less stringent than had been previously estimated. The number of acceptable beam interruptions is a function of the length of the interruption and the mission of the system. Thus, for demonstration type systems and interruption durations of 1sec < t < 5mins, and t > 5mins 2500/yr and 50/yr are deemed acceptable. However, for industrial scale power generation without energy storage type systems and interruption durations of t < 1sec., 1sec < t < 10secs., 10secs < t < 5mins, and t > 5mins, the acceptable number of interruptions are 25000, 2500, 250, and 3 respectively. However, it has also been concluded that further development is required to reduce the number of trips. It is with this in mind that the following study was undertaken. The primary focus of this study will be the merit of a multi-beam target system, which allows for multiple spallation sources within the target/blanket assembly. In this manner it is possible to ameliorate the effects of sudden accelerator beam interruption on the surrounding reactor, since the remaining beams will still be supplying source neutrons. The proton beam will be assumed to have an energy of 1 GeV, and the target material will be natural lead, which will also be the coolant for the reactor assembly. Three proton beam arrangements will be considered, first a single beam (the traditional arrangement) with an entry at the assembly center, two more options will consist of three and six entry locations. The reactor fuel assembly parameters will be based on those of the S-PRISM fast reactor proposed by GE, and the fuel composition and type will be based on that proposed by Aker Solutions for use in their accelerator driven thorium reactor. The following table summarizes the parameters to be used in this study. The isotopic composition of the fertile material is 100% Th-232, and the plutonium isotopic distribution corresponds to that characteristic of the discharge from a typical LWR, following five years of decay. Thus, the isotopic distribution for the plutonium is; Pu-238 2.5%, Pu-239 53.3%, Pu-240 25.1%, Pu-241 11.8%, and Pu-242 7.3%.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗