Metallic thorium

Work on the metallurgy of thorium is briefly reviewed. An account is given of Soviet investigations into the production of compact thorium by the method of powder metallurgy. The physico-chemical properties and the characteristics of the process of compressing electrolytic and calcium-reduced thorium powders are described. The compressibility of the calcium-reduced powder is not so good as that of the electrolytic powder, due to the lower bulk weight and the higher content of oxide films associated with the dendritic form of the particles. A theoretical analysis is given of the principal factors of the sintering process, and the variation in the strength and ductility of compact thorium obtained from electrolytic and calcium-reduced powders as a function of sinter temperature and duration is discussed.Briquets made from calcium-reduced powder without open porosity and sintered above 1150–1200 °C undergo considerable change in shape due to the volatilization of calcium. To obtain compact metal from calcium-reduced thorium powder, repeated or calibrated pressing of the sintered briquets in the cold, followed by annealing, is necessary.In conclusion, data are given for the physical and mechanical properties of thorium produced from electrolytic and calcium-reduced powders. Electrolytic thorium is more ductile ( = 35–43%) and less strong (_b 16.5 kg/mm²) than calcium-reduced thorium ( = 17–23%; _b = 22 kg/mm²).     

Measurement of 232Th(n,f) and 232Th(n,γ) reaction rates in thorium powder cylinder bombarded with D-T neutrons†

In order to provide reference for the evaluation of thorium parameters for the conceptual design of fusion–fission hybrid energy reactor, a dedicated integral experiment was carried out in a thorium powder cylinder bombarded with D-T neutrons. Thorium capture and fission rates in the 0° direction to the incident D⁺ beam were obtained using the activation method followed by the off-line gamma-ray technique, experimental uncertainties were ～3.1% for thorium capture rate, and were 5.5%, 8.1%, and 6.3% for thorium fission rates based on fission products ^85mKr, ¹⁴³Ce, and ⁸⁷Kr, respectively. The thorium fission rate based on ^85mKr agreed well with the simulation employing ENDF/B-VII.0 library data. The influence of the oxygen contained in the thorium oxide powder and the scattering neutrons from the experimental hall was also evaluated. MCNP simulations employing ENDF/B-Ⅶ.0, JENDL-4.0 library data agreed with experiment within uncertainties except that employing ENDF/B-Ⅶ.1 (6.0%) and CENDL-3.1 (7.9%) for thorium fission rate, while for thorium capture rate, simulation employing JENDL-4.0 agreed with experiment best. The influence of reaction channels of thorium transport medium employing different library data on the thorium reaction rates could be neglected according to the simulation. The thorium capture to fission ratio demonstrated that the fuel breeding efficiency is quite low and energy production plays a leading role under the neutron spectra in this experiment.     

Precipitation of Thorium or Uranium(VI) Complex Ion with Cobalt(III) or Chromium(III) Complex Cation, (II)

The precipitations of thorium and uranium(VI) sulfito complex ions with hexammine cobalt(III) chloride as the precipitant have been studied.

The orange-colored uranium(VI) precipitate obtained is [Co(NH₃)₆]₄[UO₂(SO₃)₃]₃22H₂O, which is in the form of square bipyramid, about 4 μm across in a cubic symmetry of the diamond type with a=10.40Å It decomposes to an oxide mixture of Co₃O₄ and U₃O₈ above 850°C in the air through a sulfate mixture of CoSo₄ and UO₂SO₄.

Composition of the thorium precipitate varies with the precipitation conditions. Therefore, it is considered that the thorium precipitate contains thorium hydroxide and basic thorium sulfite.     

Dynamic analysis of a thorium fuel cycle in CANDU reactors

The thorium fuel recycle scenarios through a Canada deuterium uranium (CANDU) reactor have been analyzed for two types of thorium fuel: homogeneous ThO₂UO₂ and heterogeneous ThO₂UO₂–DUPIC fuels. The recycling was performed with dry process fuel technology which has a proliferation resistance. For the once-through fuel cycle model, the existing nuclear power plant construction plan was considered up to 2016, while the nuclear demand growth rate from the year 2016 was assumed to be 0%. After setting up the once-through fuel cycle model, a thorium fuelled CANDU reactor was modeled to investigate the fuel cycle parameters. In this analysis, the spent fuel inventory as well as the amount of plutonium, minor actinides and fission products for the multiple recycling fuel cycle were estimated and compared to those of a once-through fuel cycle.     

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.     

Optimization of thorium oxalate precipitation conditions relative to derived oxide sinterability

The effect of thorium oxalate precipitation conditions on derived oxide sinterability was investigated on a laboratory scale with the objective of producing ThO₂ powder that could be sintered to high density without milling. Precipitation conditions examined were temperature, digestion time and agitation method which were employed in a two-level factorial experimental design to delineate their effects. The two levels for each of the factors, respectively, were 10 and 70°C, 15 min and 360 min, and mechanical steer and a homogenizer that imparted both mechanical and ultrasonic agitation. The ThO₂ derived from each of the precipitation trials was characterized with respect to morphology, surface area, and crystallite size as well as sinterability. Only precipitation temperature had a significant effect upon all the properties of the derived oxide powders. The most sinterable oxide was derived from an oxalate precipitated at 10°C with mechanical agitation and 15 min digestion. Pellets formed from this oxide sintered to 96% TD. Physical property data were determined also for mixed oxide derived from coprecipitated thorium?25% uranium (IV) oxalate and thoria from continuously precipitated oxalate.     

Long life small CANDLE-HTGRs with thorium

CANDLE (constant axial shape of neutron flux, nuclide densities and power shape during life of energy producing reactor) burnup strategy is applied to small (30 MWth) block-type high temperature gas-cooled reactors (HTGRs) with thorium fuel. The CANDLE burnup is adopted in this study since it has several promising merits such as simple and safe reactor operation, and the ease of designing a long life reactor core. Burnup performances of thorium fuel (²³³U, ²³²Th)O₂ are investigated for a range of enrichment ⩽15%. Discharged fuel burnup and burning region motion velocity are major parameters of its performances in this study. The reactors with thorium fuel show a better burnup performance in terms of higher discharged fuel burnup and slower burning region motion velocity (longer core lifetime) compared to the reactors with uranium fuel.     

Accelerator driven sub-critical systems with enhanced neutron multiplication

Utilisation of thorium, by way of the U-Th cycle, is of particular interest to the Indian Nuclear Power Programme because of large thorium deposits and limited Uranium reserves. Several schemes, such as fast and advanced heavy water reactors, leading to thorium utilisation, are under study at this centre. The present paper discusses a scheme for evolving a practical accelerator driven sub-critical U-Th system with increased neutron multiplication and consequentually a reduced requirement of the accelerator current. It is shown that the requirement of the accelerator current is considerably reduced if a sub-critical assembly with a given K_eff is composed of two partially coupled regions.     

Sulfurization behavior of thorium dioxide with carbon disulfide

A novel reprocessing process based on sulfide chemistry has been proposed for the recovery of nuclear materials from spent fuel. To apply the sulfide process in the thorium fuel cycle, the sulfurization behavior of thorium dioxide (ThO₂) with CS₂ was examined as a basic study. When thorium dioxide powder reacted with a mixture gas of Ar and CS₂ at different temperatures in a quartz reaction tube, the phases after the reaction were identified by the X-ray diffraction method. At temperatures lower than 673 K, ThO₂ was found to be stable because the lattice parameter of the ThO₂ phases does not change with increasing sulfurization temperatures. However, the weight gradually increased, suggesting that a small amount of sulfur was trapped in the lattice from the sulfurization. The formation of the intermediate phase ThOS was observed at 973 K. At 1073 K, both the ThOS and ThS₂ phases were observed. Finally, a single phase of ThS₂ was obtained at temperatures higher than 1173 K. The obtained results were compared with the thermodynamic consideration by using the potential diagram of the Th-S₂-O₂ system and the experimental results were in good agreement with the thermodynamic considerations.     

Measurement of the effective cross section in Th232 for thermal neutrons and the resonance integral for neutron absorption

The effective cross section in thorium for thermal neutrons (_ther = 7.31 ± 0.10 barns) and the resonance integral for thorium have been-measured in a heavy water reactor. The measurements were made by the activation method. Gold, indium, and uranium were used as comparison standards. The precise value of the effective cross section for indium for thermal neutrons is (_ther = 162 ± 10 barns) and the resonance integral in indium is (RI=2340 ± 200 barns).     

Study of thorium–uranium based molten salt blanket in a fusion–fission hybrid reactor

Not only solid fuels, but also liquid fuels can be used for the fusion–fission symbiotic reactor blanket. The operational record of the molten salt reactor with F–Li–Be was very successful, so the F–Li–Be blanket was chosen for research. The molten salt has several features which are suited for the fusion–fission applications.The fuel material uranium and thorium were dissolved in the F–Li–Be molten salt. A combined program, COUPLE, was used for neutronics analysis of the molten salt blanket. Several cases have been calculated and compared. Not only the influence of the different fuels have been studied, but also the thickness of the molten salt, and the concentration of the ⁶Li in the molten salt.Preliminary studies indicate that when thorium–uranium–plutonium fuels were added into a F–Li–Be molten salt blanket and with a component of 71% LiF–2% BeF₂–13.5% ThF₄–8.5% UF₄–5% PuF₃, and also with the molten salt thickness of 40 cm and natural concentration of ⁶Li, the appropriate blanket energy multiplication factor and TBR can be obtained.The result shows that thorium–uranium molten salt can be used in the blanket of a fusion–fission symbiotic reactor. The research on the molten salt blanket must be valuable for the design of fusion–fission symbiotic reactor.     

Effect of solid phase transformation on the solubility product of thorium hydrous oxide at 363 K

The solid phases and solubilities of thorium(IV) hydroxide after aging at 363 K were investigated in the pH_c range of 2–8 in NaClO₄ or NaCl solutions having a 0.1–3.0 mol/dm³ (M) ionic strength. Sample solutions containing solid amorphous thorium hydroxide (Th(OH)₄(am)) were prepared by the oversaturation method, and stored in a temperature chamber kept at an aging temperature (T_a) of 363 K for specified periods. The sample solutions were then cooled to 298 K for measurement of the apparent solubilities. The apparent solubilities, after aging at T_a = 363 K, decreased about 3 orders of magnitude from the solubility of Th(OH)₄(am) at T_a = 298 K. The solid phases were investigated by X-ray diffraction (XRD) in order to determine the particle sizes in the thorium hydroxide solid phases. A slight growth of the particle size of the solid phases after aging at T_a = 363 K was suggested from the obtained XRD spectrum and was correlated to the decrease of the apparent solubility at T_a = 363 K based on the particle size effect of the solubility product.     

Nuclear fission in heavy elements by high-energy particles

The results of a radiochemical investigation of nuclear fission in uranium, thorium, and bismuth by protons with an energy of 680 Mev are presented. Using an interpolation method a complete chart of the fission residue products is obtained. It is noted that there is a predominance in the production of nuclei with excess neutrons (58–64%); it is also shown that isotopes with maximum yield lie mainly in the neutron-ex cess region. The probability for symmetric fission is largest in bismuth. The cross sections for fission in uranium and thorium are 55–60% of the geometric cross section; in bismuth it is 5%. The charge distribution of fragments in fission induced by high energy protons is constant and independent of the mass number of the fission fragments and the atomic number of the fissioning nucleus. An analysis of the main features of the fission process seems to indicate that fission in uranium and thorium is due to a combined barrier-emission mechanism.     

同位素稀释-电感耦合等离子体质谱法测定八氧化三铀中微量钍

为了解决核燃料循环前端铀产品中痕量钍的分离、分析问题,将高分辨电感耦合等离子体质谱(HR-ICP-MS)与同位素稀释技术(ID)相结合,建立了灵敏、准确的八氧化三铀中微量钍的分析方法,方法的检出限为0.003 3 μg/g,相对标准偏差小于3%(n=3).     

Hydrolysis of Thorium Nitrides and Carbonitrides

Studies were made on the hydrolysis by water and water vapor of thorium nitrides—ThN, Th₃N₄, Th₂N₂O—and carbonitrides. All the thorium nitrides and carbonitrides were found to decompose in water below 100°C, changing thereby into ThO₂. The order among the thorium nitrides in their propensity toward hydrolysis is: ThC_1-xN_x>ThN>Th₃N₄>Th₂N₂O. Upon hydrolysis, ThN produced NH₃ and H₂, but in the case of the higher nitrides no H₂ was found to evolve.

In the reaction between ThN and water vapor, no higher nitride was produced, in contrast to the case of UN. The difference in behavior between ThN and UN was studied from the standpoint of differences in crystallographic conditions for the transformation from mononitride into higher nitrides. Through the hydrolysis of ThC_1-xN_x in water vapor, products containing C-C, C-C-C and C-N bonds, such as ethane and amines, were found in smaller quantities than for the case of UC_1-xN_x. This fact as well as the difficulty of formation of higher nitrides has resulted in a fairly simple hydrolysis behavior of thorium nitrides.     

应用微波消解-ICP-MS法分析环境水样中的钍

采用微波消解对环境水样进行前处理、应用电感耦合等离子体质谱法(ICP-MS)快速测定环境水样中钍含量,对测量条件和微波消解条件进行了优化,并从内标的选择、检出限、精密度、准确度、回收率以及实际样品测量等方面对结果进行分析。结果表明:以²⁰⁹Bi为内标分析水中钍时,测量结果的相对偏差最小,为0.2%～1.3%;该方法检出限为0.003μg/L;考察了4个浓度水平下的方法精密度,相对标准偏差(s_r)均小于6.0%(n=6);进行了3个不同浓度水平下的标准物质测量和加标回收率实验,测定值与标准值基本吻合,加标回收率为93.4%～106.2%;对20个实际环境水样中钍质量浓度进行了测量,测定结果在2016年测量值范围之内,验证了该法测量环境水样中钍含量的实用性。     

The separation of Pa233 without a carrier from thorium nitrate preparations irradiated by slow neutrons

The article gives a method for the separation of Pa²³³ without a carrier from thorium nitrate irradiated by slow neutrons. Pa²³³ was extracted from a thorium nitrate solution by absorption on a precipitate of MnO₂, amyl acetate extraction of the cupferron complex of protactinium with subsequent re-extraction by a citric acid solution and, finally, decomposition of the citric acid complex by oxidation with concentrated nitric acid. During this process satisfactory removal of -and--radiation was achieved. The separated radioisotope was identified by determination of its half-life. The method developed is important for obtaining the radioactive isotope Pa²³³, without a carrier which can be used as an indicator for studying the chemistry of protactinium and also for solving problems of the extraction of protactinium from naturally occurring raw material and the separation of Pa²³³ from thorium during the preparation of U²³³.     

Synthesis of thorium sol for fabricating fuel kernels

To fabricate thorium-based fuel kernel for solid fuel molten salt reactor,a component of tri-structural isotropic fuel particles is mostly based on sol-gel method.The preparation of thorium sol is an important step for fabrication of thorium-based fuel kernels,such as thorium carbide and thorium oxide.The gel quality affects the gel particle dispersion and the final products.In this work,thorium sols were prepared using Th(NO_3)_4 and NH_3·H_2O by sol-gel method.The effects of thorium concentration,mole ratio of NH_4~+/NO_3~- and reaction temperature on the pH,viscosity,turbidity,particle size and the thorium sol distribution were investigated.The results show that the viscosity and turbidity increased with the NH_4~+/NO_3~- ratio;the turbidity and colloidal particle size increased with the reaction temperature,which affected little the sol viscosity;the sol viscosity increased with the thorium concentration,which virtually did not change the turbidity;and the particle size decreased and the size distribution narrowed with increasing thorium concentration.The sol could be stored at room temperature for one day without significant property changes.Thorium gel spheres of good quality were prepared at 60℃ with the NH_4~+/NO_3~- ratio of 75-85% and the thorium concentration of 1.2-1.4 mol/L.     

Extraction of Thorium and Uranium from Chloride Solutions by Tri-n-Butyl Phosphate and Tri-n-Octyl Phosphine Oxide

The extraction of thorium and uranium chlorides by TBP and TOPO was studied. The composition of complexes extracted from the chloride solutions of low acid concentration was established by partition study to be UO₂Cl₂ (TOPO)₂, UO₂Cl₄ (TOPO)₂, UO₂Cl₄ (TOPO)₂ and UCl₄ (TBP)₂. Composition of the thorium complex in the TBP phase free from hydrochloric acid was revealed by infrared study to be ThCl₄ (TBP)4. The extraction behavior of thorium chloride by TBP was different from that of U (N) and Pu(N) chloride, and the composition of the complex was presumed to be HThCl₅(TBP)₄ in the extraction from concentrated chloride solution containing hydrochloric acid.     

Sorption studies of uranium and thorium on activated carbon prepared from olive stones: Kinetic and thermodynamic aspects

Activated carbon prepared by the chemical activation of olive stone was examined for the sorption of uranium and thorium from aqueous solutions. Precursor/activating agent (ZnCl₂) ratio (1:2) and 500 °C carbonization temperature were used for the preparation of the sorbent. The total sorption capacities were found to be 0.171 and 0.087 mmol g^?1 for uranium and thorium, respectively. The sorption of uranium and thorium was studied as a function of shaking time, pH, initial metal ion concentration, temperature and adsorbent concentration in a batch system. The sorption followed pseudo-second-order kinetics. ΔH° and ΔS° values for thorium and uranium sorption were calculated from the slope and intercept of plots of ln K_d versus 1/T. The positive values of ΔH° indicate the endothermic nature of the process for both metals and decrease in the value of ΔG° with rise in temperature show that the sorption is more favorable at high temperature.