ThO2 Research Articles

Betterment in EDXRF analytical results for compositional characterization of mixed uranium thorium oxide samples with bead specimens compared with pressed pellet specimens

A comparative study on the energy dispersive X‐ray fluorescence analytical results of uranium determinations, in uranium and uranium–thorium mixed oxides, using specimens in the form of fused beads and pressed pellets, has been made. It was observed that in case of fusion bead specimens, the intensity of the analyte lines was approximately 1.6 times of that observed in pellet specimens under identical instrumental conditions. In case of uranium oxide samples, the analytical results with bead specimens were slightly better compared with the pellet specimens. However, in case of the uranium–thorium oxide mixtures, the average precision obtained with bead specimen was significantly better (1%, 1 s) in comparison with that achieved using pellet specimens (7%, 1 s). This difference may be due to the hardness of thorium oxide compared with uranium oxide, which affects the homogeneity of the pellet specimens prepared. In fusion bead method of sample preparation, even highly refractory material like ThO2 forms uniform glass beads. Addition of internal standard further improves the analytical results, with reduction in the percent deviation of energy dispersive X‐ray fluorescence results from the expected values to 3% from 7% compared with that obtained using without internal standard. The fusion bead method of sample preparation will be very useful for characterization of sintered (U,Th)O2 pellets, which are highly refractory and difficult to dissolve. Copyright © 2016 John Wiley & Sons, Ltd.

Multiparametric study of thorium oxide dissolution in aqueous media

Abstract Thorium oxide is poorly soluble: unlike uranium oxide, concentrated nitric acid medium is not sufficient to get quantitative dissolution. Addition of small amounts of fluoride is required to achieve thorium oxide total dissolution. The effect of several parameters on thorium oxide dissolution in order to optimize the dissolution conditions is reported in this paper. Thus the influence of solid characteristics, dissolution method, temperature and composition of dissolution medium on ThO2 dissolution rate has been studied. No complexing agents tested other than fluoride allows total dissolution. Beyond a given HF concentration a decrease of the dissolution rate is observed due to the formation of a precipitate at the solid/solution interface. It was demonstrated by XPS measurements that this precipitate is constituted of thorium fluoride (ThF4) formed during the ThO2 dissolution. The low concentration of HF required to achieve a total dissolution and the activation energy value measured tends to show a catalytic effect of HF on the dissolution process.

First Principles Study of the Structure and Elastic Properties of Thorium Metal

ABSTRACTThorium has long been considered a possible source of fuel for use in power generating nuclear reactors. While much attention and interest have focused on thorium oxide, metallic thorium alloys were investigated in the past as fuel candidates for fast and thermal breeder reactors. In this work, thorium’s two solid allotropes (face centered cubic α and body centered cubic β) are modelled using Density Functional Theory (DFT). The Vienna Ab Initio Simulation Package (VASP) is used to determine structural and elastic properties, as well as the density of states. The Voigt-Reuss-Hill approximations are used to predict the phases’ bulk moduli, shear moduli, Young’s moduli, and Poisson’s ratios. Four exchange-correlation potentials are used and compared. These are the LDA, the PBE-GGA, the RPBE, and the PBEsol. All potentials showed relatively good accuracy when predicting the lattice constant. The RPBE was the most accurate, slightly over predicting by < 0.2%. The RPBE and the PBE-GGA were the most accurate in predicting elastic properties, performing almost equally, while slightly over predicting most values.

Potential to raise the efficiency of neutron and neutron–photon therapy using metal nonradioactive nanoparticles

The use of metal nonradioactive nanoparticles (specifically, gold ones) in neutron and neutron–photon cancer therapy is proposed. The minimum therapeutically effective average density of gold within a tumor subjected to neutron irradiation is estimated as a value on the order of 10-5-10-4 g/cm3. Potential benefits of the use of data obtained when using Peteosthor (a drug containing 224Ra and colloidal platinum) and Thorotrast (a radiopaque contrast agent containing thorium oxide nanoparticles) and its analogues in the analysis of safety and efficiency of application of nonradioactive nanoparticles in radiation therapy and diagnostics are discussed.

Monte Carlo Simulation of Inclined Reactivity Control Rod and Boron Poisoning for the Canadian-SCWR Supercell

The Canadian-SCWR is a heavy-water moderated supercritical light-water-cooled pressure tube reactor. It is fueled with CANada deuterium uranium (CANDU)-type bundles (62 elements) containing a mixture of thorium and plutonium oxides. Because the pressure tubes are vertical, the upper region of the core is occupied by the inlet and outlet headers render it nearly impossible to insert vertical control rods in the core from the top. Insertion of solid control devices from the bottom of the core is possible, but this option was initially rejected because it was judged impractical. The option that is proposed here is to use inclined control rods that are inserted from the side of the reactor and benefit from the gravitational pull exerted on them. The objective of this paper is to evaluate the neutronic performance of the proposed inclined control rods. To achieve this goal, we first develop a three-dimensional (3D) supercell model to simulate an inclined rod located between four vertical fuel cells. Simulations are performed with the SERPENT Monte Carlo code at five axial positions in the reactor to evaluate the effect of coolant temperature and density, which varies substantially with core height, on the reactivity worth of the control rods. The effect of modifying the inclination and spatial position of the control rod inside the supercell is then analyzed. Finally, we evaluate how boron poisoning of the moderator affects their effectiveness.

Dissolution Study of Thorium-Uranium Oxides in Aqueous Triflic Acid Solutions

The dissolution of sintered mixed oxides of thorium with uranium in various concentrations of trifluoromethanesulfonic (triflic) acid solutions was investigated under reflux conditions to evaluate the suitability of the method. Various fragment sizes (1.00mm <x < 7.30mm) of sintered (Th,U)O2 and simulated high-burnup nuclear fuel (SIMFUEL) were almost completely dissolved in a few hours, which implies that triflic acid could be used as an alternative to the common dissolution method, involving nitric acid-hydrofluoric acid mixture. The influence of acid concentration, composition of the solids, and reaction time on the dissolution yield of Th and U ions was studied using Inductively Coupled Plasma - Mass Spectrometry (ICP-MS). The dissolution rate was found to depend upon the triflic acid concentration and size of the solid fragments, with near complete dissolution for the smallest fragments occurring in boiling 87% w/w triflic acid. The formation of Th and U ions in solution appears to occur at the same rate as the triflic acid simultaneously reacts with the constituent oxides as evidenced by the results of a constant U/Th concentration ratio with the progress of the dissolution.

Three-component U-Pu-Th fuel for plutonium irradiation in heavy water reactors

This paper discusses concepts for three-component fuel bundles containing plutonium, uranium and thorium for use in pressurised heavy water reactors, and cases for and against implementation of such a nuclear energy system in the United Kingdom. Heavy water reactors are used extensively in Canada, and are deploying within India and China, whilst the UK is considering the use of heavy water reactors to manage its plutonium inventory of 140 tonnes. The UK heavy water reactor proposal uses a mixed oxide (MOX) fuel of plutonium in depleted uranium, within the enhanced CANDU-6 (EC-6) reactor. This work proposes an alternative heterogeneous fuel concept based on the same reactor and CANFLEX fuel bundle, with eight large-diameter fuel elements loaded with natural thorium oxide and 35 small-diameter fuel elements loaded with a MOX of plutonium and reprocessed uranium stocks from UK MAGNOX and AGR reactors. Indicative neutronic calculations suggest that such a fuel would be neutronically feasible. A similar MOX may alternatively be fabricated from reprocessed <5% enriched light water reactor fuel, such as the fuel of the AREVA EPR reactor, to consume newly produced plutonium from reprocessing, similar to the DUPIC (direct use of PWR fuel in CANDU) process.

Actinide chemistry using singlet-paired coupled cluster and its combinations with density functionals.

Singlet-paired coupled cluster doubles (CCD0) is a simplification of CCD that relinquishes a fraction of dynamic correlation in order to be able to describe static correlation. Combinations of CCD0 with density functionals that recover specifically the dynamic correlation missing in the former have also been developed recently. Here, we assess the accuracy of CCD0 and CCD0+DFT (and variants of these using Brueckner orbitals) as compared to well-established quantum chemical methods for describing ground-state properties of singlet actinide molecules. The f(0) actinyl series (UO2(2+), NpO2(3+), PuO2(4+)), the isoelectronic NUN, and thorium (ThO, ThO(2+)) and nobelium (NoO, NoO2) oxides are studied.

Fabrication of MWCNTs/ThO2 nanocomposite and its adsorption behavior for the removal of Pb(II) metal from aqueous medium

Multiwall carbon nanotubes (MWCNTs) were chemically modified to form nanocomposite with thorium oxide. The MWCNTs/ThO2 nanocomposite was characterized using different modern techniques including Fourier transform infrared spectroscopy, X-ray powdered diffraction, scanning electron microscope, and transmission electron microscope. The average size of MWCNTs/ThO2 nanocomposite was in the range from 5 to 10 nm. The nanocomposite material was investigated for its adsorption behavior for Pb(II) ions removal from its aqueous system. For the adsorption of Pb(II) by MWCNTs/ThO2, the equilibrium was achieved within 50 min. The temperature and pH have also found to play important role in the adsorption process and maximum adsorption was found at 45°C and pH 5.5.

Preparation of UO2, ThO2 and (Th,U)O2 pellets from photochemically-prepared nano-powders

Photochemically-induced preparation of nano-powders of crystalline uranium and/or thorium oxides and their subsequent pelletizing has been investigated. The preparative method was based on the photochemically induced formation of amorphous solid precursors in aqueous solution containing uranyl and/or thorium nitrate and ammonium formate. The EXAFS analyses of the precursors shown that photon irradiation of thorium containing solutions yields a compound with little long-range order but likely “ThO2 like” and the irradiation of uranium containing solutions yields the mixture of U(IV) and U(VI) compounds. The U-containing precursors were carbon free, thus allowing direct heat treatment in reducing atmosphere without pre-treatment in the air. Subsequent heat treatment of amorphous solid precursors at 300–550 °C yielded nano-crystalline UO2, ThO2 or solid (Th,U)O2 solutions with high purity, well-developed crystals with linear crystallite size <15 nm. The prepared nano-powders of crystalline oxides were pelletized without any binder (pressure 500 MPa), the green pellets were subsequently sintered at 1300 °C under an Ar:H2 (20:1) mixture (UO2 and (Th,U)O2 pellets) or at 1600 °C in ambient air (ThO2 pellets). The theoretical density of the sintered pellets varied from 91 to 97%.

PLASMA-CHEMICAL SYNTHESIS OF URANIUM AND THORIUM OXIDES COMPOUNDS FROM NITRIC SOLUTIONS

The article shows results of research of obtaining uranium and thorium oxides in air plasma from burning water-organic compositions based on nitric solutions and ethanol (acetone). Authors estimate formulations of burning compositions and process modes that provide direct and energy-efficient obtaining oxide compositions UO 2 –ThO 2 . Findings could be used to create plasma technology of obtaining homogenous uranium and thorium oxide compounds for thorium fuel fabrication.

Neutronics analysis of blankets for a hybrid fusion neutron source

Modern challenges of nuclear power concern a potential shortage of nuclear fuel for fission reactors in the case of intensive development of the nuclear industry, insufficient development of economic and safe fast reactors, underutilization of the closed fuel cycle, spent nuclear fuel reprocessing, nuclear power safety and nonproliferation of weapon-grade materials. Expected progress in solving these problems is associated with the development of a hybrid fusion neutron source (FNS) with a subcritical blanket, using the closed nuclear fuel cycle. In this work the capability of hybrid fusion neutron source blankets in the generation of 233U, 239Pu and 3H nuclides, reprocessing of spent nuclear fuel, electricity and heat production are investigated. The basic kinds of blankets are considered. There is a uranium and thorium solid-state blanket, a blanket with the use of heavy water solutions of salts, oxides of uranium and thorium, a molten lead and a molten salt blanket. The structure and geometrical parameters of the blankets, the moderators, and the fertile materials are optimized to obtain the ultimate nuclear fuel yield at the minimal accumulation of radiation toxic wastes. The neutronics comparative analysis of the different blanket models is presented. In the results, the optimal FNS blanket models have been chosen.

Synthesis and characterization of ultra-fine well-dispersed thoria nano spheres through reduction reactions in nitrate bath

In most applications we need to use thoria with sintered density of 95% TD which is usually achieved at temperatures above 2073 K. Thus, it is an expensive and energy consuming process. Recent researches have shown that the nanocrystalline phase of thorium oxide can be sintered to a density of 9.6 × 106 g m−3 at low temperature (1573 K). Therefore, the synthesis of thoria nanostructures obviously is attracting increasing attention recently. The strategy developed in this study, offers significant advantages (simplicity and cleanness of method and also a phase purity and new morphology of the product) over the conventional routes for the synthesis of ThO2 nanostructure. Electrochemical preparation of nanocrystalline thorium oxides based on base generation at the electrode surface in aqueous solutions containing thorium nitrate was studied. Subsequent heat treatment under air atmospheres leads to formation of the pure phase of nanocrystallineThO2 at 1000 °C. The synthesized powder was characterized by means of Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Transmission Electron microscopy (TEM, Phillips EM 2085) Brunauer–Emmett–Teller (BET) and Fourier transform Infrared (FT-IR) spectroscopy. The obtained product consisted of uniform nanospheres from 20 to 50 nm in diameter with narrow size distribution. To the best of our knowledge, this is first attempt to quantitatively synthesize ThO2 nanosphere by the base generation procedure.

Probing local coordination and oxidation state of uranium in ThO2: U nanostructured

Uranium doped thorium oxide nanoparticle (UDT) was synthesized using citric acid assisted combustion method. The concentration of uranium was varied from 0.5 to 5.0 mol % to investigate the effect of doping concentration on its optical properties. The synthesised UDT powder were characterized systematically using X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) respectively for phase purity, morphology and crystallinity. Pertaining to nuclear industry, UDT is an important material and investigating the local structure of uranium in UDT is interesting as well as challenging because of complexity involved in synthesis of such ceramic powder. We have used time resolved photoluminescence spectroscopy (TRPLS) to probe the local coordination and oxidation state of uranium in UDT. Based on PL emission spectroscopy it was confirmed that uranium stabilizes as UO22+ ion in UDT. Lifetime spectroscopy shows that uranyl ion is not homogenously distributed in UDT lattice; rather it has two different chemical environments. Effect of concentration on PL behaviour shows that, concentration quenching takes place beyond 2.0 mol %; and based on critical distance calculation multipolar interaction was found to be responsible for such non-radiative quenching. As far as application in luminescence industry is concerned PL measurement shows that UDT gives intense green emission under UV excitation.

Neutronic performance of (ReprocessedU/Th)O2 fuel in CANDU 6 reactor

Abstract Utilization of thorium-based fuel in different reactors has been under investigation for several decades. In fact, excellent breeding features, rather flattened distribution of power as well as proliferation resistance of such fuel cycle draws the attention towards utilization of this type of fuel in nuclear power technology. In the present study, the neutronic performance of a typical thorium core loading is addressed. In this configuration, a mixed uranium and thorium oxide is loaded in CANDU 6 reactor. The obtained results determine a total peaking factor of 2.73 for the proposed configuration. The values obtained for the β and the βeff are 332 and 303 pcm respectively. The core reactivity coefficients were more negative comparing the CANDU 6 loaded with natUO2. The initial fissile material loaded in the core increased by a factor of 1.5 after 730 GWd burn-up. The obtained burn-up results show the core reactivity variations were highly positive after 6 and 12 h shut down because of considerably high buildup of 233Pa after 1-year core operation at 2000 MW power.

A novel process for the synthesis of “Designed Molecular Precursor” (DMP) of thorium useful for broad application spectrum

For the first time (Patent application filed in India vide N/F No- 0018NF2015) a novel process for the synthesis of “Designed Molecular Precursor” (DMP) of thorium has been developed, which involves the unique combination of two different (dual) capping agents, one is biomolecule: Cytosine and other is non biomolecule : cetyl trimethyl ammonium bromide. The DMP essentially consists of hybrid nanosized thorium oxalate and alkaline thorate whose application lies in the area of making thorium metal, densified thorium oxide, carbide and nitride, anhydrous thorium complexes and thorium boron silicates glasses.

Characterization of theI(|Ω|=1)–X1Σ+(0,0)band of thorium oxide

The $I(|\ensuremath{\Omega}|=1)\phantom{\rule{1.0pt}{0ex}}--\phantom{\rule{1.0pt}{0ex}}X\phantom{\rule{0.28em}{0ex}}{}^{1}{\ensuremath{\Sigma}}^{+}(0,0)$ band near 512 nm of thorium oxide has been recorded and analyzed field free and in the presence of both static electric and magnetic fields. The determined ${T}_{00}$, $B$, and $q$ field-free parameters for the $I(|\ensuremath{\Omega}|=1)(v=0)$ state are $(\text{in}\phantom{\rule{5.0pt}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1})19539.3823\ifmmode\pm\else\textpm\fi{}0.0003,0.328 69\ifmmode\pm\else\textpm\fi{}0.000 03$, and 0.001 54 \ifmmode\pm\else\textpm\fi{} 0.000 05. The Zeeman-induced shifts and splittings of the low-$J$ lines were analyzed to determine $g$ factors and suggest that the $I(|\ensuremath{\Omega}|=1)(v=0)$ state has a dominant ${}^{1}\ensuremath{\Pi}$ character. The Stark tuning of the low-$J$ lines was analyzed to determine the permanent electric dipole moment ${\ensuremath{\mu}}_{\mathrm{el}}$ for the $I(|\ensuremath{\Omega}|=1)(v=0)$ state of 4.25 \ifmmode\pm\else\textpm\fi{} 0.02 D.

Local Electrochemical Deposition of Thorium on SiO2/Si(111) Surface

The paper presents the results of the study of local formation of thorium oxide coatings on SiO2/Si(111) surface by electrochemical deposition. It was found that the electrochemical deposition of thorium atoms from thorium nitrate solution of Th(NO3)4 with the presence of water on silicon surface results in local formation of thorium compounds. The results of surface analysis by local XPS indicate that these compounds represent a thorium-, silicon-, oxygen- and carbon-based compounds. After 6hours annealing at 600°C at atmosphere carbon pulled completely, and the cluster formed film consists of oxygen and thorium only. It was shown that this system can be promising for further research of nuclear low-lying isomeric transition in 229Th isotope when irradiated by an electron beam.

Branching ratios and radiative lifetimes of theU,L, andIstates of thorium oxide

The dispersed laser induced fluorescence resulting from excitation of the $U(|\ensuremath{\Omega}|=1)\ensuremath{-}X{}^{1}{\ensuremath{\Sigma}}^{+}(0,0)$, $L(|\ensuremath{\Omega}|=1)\ensuremath{-}X{}^{1}{\ensuremath{\Sigma}}^{+}(0,0)$, and $I(|\ensuremath{\Omega}|=1)\ensuremath{-}X{}^{1}{\ensuremath{\Sigma}}^{+}(0,0)$ bands near 398, 402, and 512 nm, respectively, of thorium oxide, ThO, has been recorded and analyzed. The branching ratios for the fluorescence decay from the $U(|\ensuremath{\Omega}|=1)(v=0)$, $L(|\ensuremath{\Omega}|=1)(v=0)$, and $I(|\ensuremath{\Omega}|=1)(v=0)$ states are determined. Radiative lifetimes of 57 \ifmmode\pm\else\textpm\fi{} 2, 17 \ifmmode\pm\else\textpm\fi{} 1, 115 \ifmmode\pm\else\textpm\fi{} 4, and 468 \ifmmode\pm\else\textpm\fi{} 30 ns for the $U(|\ensuremath{\Omega}|=1)(v=0)$, $L(|\ensuremath{\Omega}|=1)(v=0)$, $I(|\ensuremath{\Omega}|=1)(v=0)$, and $C{}^{1}{\ensuremath{\Pi}}_{1}(v=0)$ states, respectively, were determined from the analysis of the fluorescence decay curves. Transition dipole moments for numerous bands involving the $U(|\ensuremath{\Omega}|=1)(v=0)$, $L(|\ensuremath{\Omega}|=1)(v=0)$, $I(|\ensuremath{\Omega}|=1)(v=0)$, and $C{}^{1}{\ensuremath{\Pi}}_{1}(v=0)$ states are determined. Possible optical pumping and detection schemes are proposed for experiments using ThO to search for the electric dipole moment of the electron.

Burn-up calculation of different thorium-based fuel matrixes in a thermal research reactor using MCNPX 2.6 code

Abstract Decrease of the economically accessible uranium resources and the inherent proliferation resistance of thorium fuel motivate its application in nuclear power systems. Estimation of the nuclear reactor’s neutronic parameters during different operational situations is of key importance for the safe operation of nuclear reactors. In the present research, thorium oxide fuel burn-up calculations for a demonstrative model of a heavy water- -cooled reactor have been performed using MCNPX 2.6 code. Neutronic parameters for three different thorium fuel matrices loaded separately in the modelled thermal core have been investigated. 233U, 235U and 239Pu isotopes have been used as fissile element in the thorium oxide fuel, separately. Burn-up of three different fuels has been calculated at 1 MW constant power. 135X and 149Sm concentration variations have been studied in the modelled core during 165 days burn-up. Burn-up of thorium oxide enriched with 233U resulted in the least 149Sm and 135Xe productions and net fissile production of 233U after 165 days. The negative fuel, coolant and void reactivity of the used fuel assures safe operation of the modelled thermal core containing (233U-Th) O2 matrix. Furthermore, utilisation of thorium breeder fuel demonstrates several advantages, such as good neutronic economy, 233U production and less production of long-lived α emitter high radiotoxic wastes in biological internal exposure point of view