Selectivity of Alkali Metal Ion and Lithium Isotopes on Ion Exchangers in H Form Prepared from LiTi x Zr2-x (PO4)3 (x=0, 1)

Inorganic metal (IV) phosphate-based ion exchanges in the hydrogen form, HTi _x Zr_2-x (PO₄)₃ (x =0, 1), have been prepared by leaching lithium ions from the precursors, LTi _x Zr_2-x (PO₄)₃ (x=0, 1), through ion exchange with protons. The degrees of leaching of lithium ion were more than 99%. Both ion exchangers showed high selectivity toward lithium and sodium ions and little affinity to rubidium and cesium ions among alkali metal ions. The lithium ion uptakes from aqueous solutions were monotonously increasing functions of pH. Isotopically, both ion exchangers were ⁶Li-specific like other inorganic ion exchangers so far examined. The ⁷Li-to-⁶Li isotopic single-stage separation factor, S, of HTiZr(PO₄)₃ was larger than that of HZr₂(PO₄)₃ at a given pH-value. The relatively large S-values of 1.022 and 1.042 were found for HZr₂ (PO₄)₃ for HTiZr(PO₄)₃, respectively, at 25°C when the pH of the solution phase was around 5.     

Immobilization of Cs and Sr to HZr2(PO4)3 using an autoclave

The proton-type crystalline zirconium phosphate, HZr₂(PO₄)₃, was prepared by a thermal decomposition of NH₄Zr₂(PO₄)₃ at about 450 °C, where NH₄Zr₂(PO₄)₃ was obtained in advance by a hydrothermal synthesis using a mixed solution of ZrOCl₂, H₃PO₄ and H₂C₂O₄. Cs or Sr ion was immobilized to HZr₂(PO₄)₃ by mixing HZr₂(PO₄)₃ with an aqueous solution of CsNO₃ or Sr(NO₃)₂ under the molar ratio CsNO₃/HZr₂(PO₄)₃ = 1.0 or Sr(NO₃)₂/HZr₂(PO₄)₃ = 0.5. The mixtures were treated thermally in an autoclave at different temperatures from 200 to 275 °C and Arrhenius equation was applied to the Cs and Sr immobilization process to HZr₂(PO₄)₃. The activation energy for the immobilization process of Cs or Sr was estimated as 179 kJ mol^?1 and 186 kJ mol^?1, respectively.     

Effect of the preparation conditions of zirconium phosphate on the characteristics of Sr immobilization

The proton-type crystalline zirconium phosphate, HZr₂(PO₄)₃, was obtained by a thermal decomposition of NH₄Zr₂(PO₄)₃ at different temperatures from 400 to 800 °C, where NH₄Zr₂(PO₄)₃ was obtained in advance by a hydrothermal synthesis using a mixed solution of ZrOCl₂, H₃PO₄ and H₂C₂O₄ with different processing times from 5 to 72 h. Sr ion was immobilized to HZr₂(PO₄)₃ by treating the mixture of HZr₂(PO₄)₃ and Sr(NO₃)₂ aqueous solution in an autoclave at 250 °C. Immobilizing and leaching performance of St in HZr₂(PO₄)₃ were discussed.     

Thermodynamic model for Zr solubility in the presence of gluconic acid and isosaccharinic acid

Zr solubility in the presence of gluconic acid (GLU) and isosaccharinic acid (ISA) was investigated as a function of hydrogen ion concentration (pH_c) and the total concentration of GLU or ISA. The dependence of the increase in Zr solubility on the pH_c and GLU concentration suggested the existence of Zr(OH)₄(GLU)₂^2? in the neutral pH region and Zr(OH)₄(GLU)(GLU_-H)^3? in the alkaline pH region above pH_c 10 as the dominant species in the presence of 10^?3–10^?1 mol/dm³ (M) GLU. In the presence of ISA, the dominant species Zr(OH)₄(ISA)₂^2? and Zr(OH)₄(ISA)(ISA_-H)^3? were proposed to occur in the neutral and alkaline pH regions, similar to those found in the presence of GLU. From X-ray diffraction analysis, the solubility-limiting solid phase in the presence of GLU and ISA was considered to be Zr(OH)₄(am). The formation constants of the Zr gluconate and isosaccharinate complexes were determined by least-squares fitting analysis of the solubility data, and the obtained values were discussed in comparison with those of tetravalent actinides.     

“The Third Phase” of Extraction Processes in Fuel Reprocessing, (I)

Formation conditions, compositions and structures of precipitates or “the third phase” were systematically examined in the systems of Zr and radiation depleted products of TBP, such as HDBP, H₂MBP, H₃PO₄, by means of elemental analysis, X-ray diffraction, infrared spectra and ¹H-NMR. It was confirmed that one of the most important origins for the third phase is a complexation between Zr ion and the depleted products of TBP. Followings were also elucidated:

(1) When the depleted products co-exist with each other, the cooperative effects on the precipitate formation appear in low acid solutions.

(2) Precipitate formation depends on the mole ratio of HDBP/Zr. The amount of precipitate reaches the maximum at the mole ratio of approximately 2 and decreases with increasing concentration of HDBP and finally disappears at approximately 10.

(3) Precipitate formed at the mole ratio of approximately 2 has the chemical formula, Zr (NO₃)₂ (HDBP)₂ (OH)₂.

(4) Precipitates of the Zr-H₂MBP system begin to appear at the concentration of H₂MBP in one order of magnitude smaller than that of HDBP in Zr-HDBP system.

(5) Precipitates of Zr-H₂MBP system have no NO₃ ion and a basic structure of Zr-(HMBP)₂(OH)₂ with an interlayer distance of 16 Å.     

Ion beam analysis of partial lithium extraction of LiMn2O4 by chemical delithiation

Lithium manganese oxide, LiMn₂O₄, has been studied by many research groups. This material is a great candidate to be used as positive electrode in rechargeable lithium-ion batteries because of its low cost, abundant precursors and non-toxicity. LiMn₂O₄ has a spinel Fd-3m structure and shows a reversible extraction and insertion of lithium ions that is one of the most important characteristic of positive electrodes in rechargeable batteries.In this work, LiMn₂O₄ samples were synthesized by solid state reaction. A partial lithium removal was performed on this system by chemical delithiation using HCl aqueous solutions at different concentrations. Six partial-extracted compounds were obtained and characterized by Ion beam analysis (IBA) in order to obtain the Li concentrations. X-ray diffraction (XRD) and Rietveld analyses were also performed. A rigorous study of lithium contents is critical to analyze the structure properties of these compounds and samples production parameters. The IBA method used in this work was the analysis of energy spectra of elastic backscattered (EBS) proton from Mn, O and Li nuclei and the α-particles energy from the ⁷Li(p,α)⁴He nuclear reaction (NR).     

The FeSe2(cr) solubility determined by solubility experiments of Se co-existing with Fe

To determine the equilibrium constant for ferroselite (FeSe₂(cr)) dissolution reaction, FeSe₂(cr) solubility experiments were performed at 298 ± 1 K from both the over- and under-saturation directions with Fe–Se precipitates that were aged at 348 K. X-ray diffraction (XRD) analysis detected only FeSe₂(cr) as the Se solid phase in the equilibrated precipitates. The E_h values of the equilibrated suspensions ranged from ?188.6 to ?4.9 mV vs. standard hydrogen electrode (SHE) and the pH values ranged from 6.00 to 8.76. Based on the available thermodynamic data, Se₄^2? and Fe²⁺ are thermodynamically stable within this E_h–pH range. Agreement between the solubility data obtained from the over- and under-saturation directions lends credence to the attainment of equilibrium at 298 ± 1 K. The thermodynamic interpretations using the specific ion interaction theory (SIT) model showed that E_h values and the concentrations of Se and Fe are well represented by the 2FeSe₂(cr) solubility reaction (2FeSe₂(cr) ? 2Fe²⁺ + Se₄^2? + 2e^?) with log₁₀K^○ = ?17.09 ± 0.28. The obtained log₁₀K^○ value falls within the uncertainty limits of the log₁₀K^○ value calculated from the available thermodynamic data.     

Preparation and characterization of lithium-titanate pebbles by solid-state reaction extrusion and spherodization techniques for fusion reactor

For the development of TBM for fusion reactors, lithium containing ceramics as against the metal are preferred as tritium breeding material. Lithium titanate (Li₂TiO₃) is one such chosen ceramic tritium breeder. Li₂TiO₃ pebbles are conventionally prepared by sol-gel process and wet process. Solid state reaction of lithium carbonate with titanium dioxide is preferred route for the bulk production of Li₂TiO_3. Thermo-gravimetric and differential thermal analysis (TG-DTA) techniques have been used in the present study to understand the solid state reaction of intimate mixture of lithium carbonate and titanium dioxide. It was found out that single phase lithium titanate (Li₂TiO₃) is produced at 750 °C and the reaction is completed in 6 h. Fine powders of lithium titanate obtained after milling and classification were mixed with aqueous solution of PVA to prepare green pebbles of desired size and shape. The pebbles were subsequently sintered at 900 °C and the effect of sintering time on the properties of sintered pebbles was studied. The reaction mechanisms and the product qualities obtained by the solid state reaction, extrusion and spherodization techniques are discussed in this paper.     

烧绿石(La1-yNdy)2Zr2O7模拟固化241Am的晶体结构稳定性研究

为研究²⁴¹Am在La₂Zr₂O₇烧绿石中的固化行为及其对烧绿石晶体结构稳定性的影响,实验选用Nd作为²⁴¹Am的模拟物,采用Sol-喷雾热解法合成了(La_1-yNd_y)₂Zr₂O₇（0.0≤y≤1.0）系列样品,并借助X射线衍射和振动光谱手段对样品的晶体结构稳定性进行了研究。实验结果表明：随着Nd掺杂量的增加,O48f位置参数x_48f和I₍₁₁₁₎ /I₍₂₂₂₎均呈规律性增大,Raman谱逐渐展宽,IR谱发生蓝移,所有结果均证实用Nd不断替换La将导致烧绿石晶体结构有序化程度逐渐降低。另外,实验发现掺杂量y≈0.8是烧绿石晶体结构发生几何相变的逾渗阈值,超过该阈值有序的烧绿石结构将发生突变进而加速向无序萤石结构转变,该实验结果可为(La_1-yAm_y)2Zr2O7固溶体的结构稳定性研究提供参考。     

EPR Study of Uranium (V) Species in Photo-and Electrolytic Reduction Processes of UO2 NO3)2-2TBP

Abstract

Electron Paramagnetic Resonance (EPR) and optical spectra of uranium(V) species were observed in both processes of photo- and electrolytic reduction of UO₂(NO₃)₂-2tributylphosphate (TBP) in 80%TBP-n-dodecane solution. The formation of U(V) species was detected by an optical spectrum (λ_max: 770, 970 and 1,420 nm). EPR signal with the value of ff-factor –2.3 and a linewidth of approximately 1,100 Gs was observed during the electrolytic reduction. On the other hand, during the photoreduction the signal with the value of fil-factor –1.94 was observed and there was found a superhyperfine structure with the intensity ratio of 1:2:1, that is caused by the superhyperfine coupling with nuclear spin, I=1/2, of the strongly coordinated ³¹P to the central uranium through oxygen atom. The superhyperfine coupling constant was estimated to be 27 Gs. Moreover, the signal with the value of g-factor –2.00 due to an organic radical was observed. The residue after the thermo-gravimetric analysis of UO₂(NO₃)₂-2TBP was identified as α-UP₂O₇ by the powder X-ray diffraction analysis, indicating the strong coordination of TBP to the central uranium atom.     

Ion irradiation effects on tungsten-oxide films and charge state effect on electronic erosion

We have studied electronic- and atomic-structure modifications of polycrystalline WO₃ films (bandgap of ∼3 eV) by ion irradiation. WO₃ films were prepared by oxidation of W films on MgO substrates and of W sheets. We find disordering or amorphization, the lattice expansion of ∼1.5% and bandgap increase of 0.2 eV after 90 MeV Ni ion irradiation at ∼3 × 10¹² cm⁻². A broad peak of optical absorption appears around 1.6 μm by ion irradiation. We also find that the erosion yield by high-energy ions with the equilibrium charge exceeds 10⁴ and that the erosion yield under ion impact with non-equilibrium charge (90 MeV Ni⁺¹⁰) is ∼1/5 of that with the equilibrium charge (89 MeV Ni⁺¹⁹). Effects of depth dependence of the ion mean charge on the erosion yields are discussed. The erosion yield by low-energy ions is also presented.     

Oxygen deficiency and excess of rutile titania (1 1 0) surfaces analyzed by ion scattering coupled with elastic recoil detection

Oxygen deficiency and excess of rutile titania (TiO₂) surfaces are important factors for catalytic activities of metal nano-particles on the TiO₂ supports. Medium energy ion scattering (MEIS; 80 keV He⁺) coupled with elastic recoil detection analysis (ERD; 150 keV Ne⁺) can determine the numbers of bridging O (O_br) vacancies (V_O) and excess O atoms adsorbed on the 5-fold Ti rows of TiO₂(1 1 0) surfaces. The amounts of V_O and adsorbed O were derived by H₂O and ¹⁸O₂ exposure followed by ERD and MEIS analyses, respectively. The present analysis revealed that only about a half of V_O are filled and a comparable amount of O atoms are adsorbed on the reduced TiO₂(1 1 0) surface after exposure to O₂ (1000 L; 1 L = 1 × 10⁻⁶ Torr s) at room temperature (RT). We also detected the adsorbed O for the hydroxylated TiO₂(1 1 0) after ¹⁸O₂ exposure at RT. Finally, it is shown that the O adsorbed on the Ti rows reacts with CO probably to form CO₂ at RT. Based on the results obtained here, we clarify the reason why only a half of V_O are filled by exposing reduced surface to O₂ at RT and what is the primary source of subsurface excess electronic charge, which acts as a leading part of the surface electrochemistry and gives the defect state in the band gap seen in the valence band spectra for reduced and hydroxylated TiO₂(1 1 0) surfaces.     

Structural and Electrochemical Studies on Uranium(VI) Nitrato Complex with n-Octyl(phenyl)-N,N-Diisobutylcarbamoylmethylphosphine Oxide in Non-aqueous Solvents

The structure of uranyl nitrato complex with CMPO [n-Octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide] in solid state and in non-aqueous solvents without containing free CR/IPO has been studied by using IR spectrophotometer, ¹³C- and ³¹P-NMR. The carbonyl(vcO) and phosphoryl(vpO) stretching bands of coordinated CMPO were observed at lower wavenumber than the corresponding bands of free CMPO in both the states. The ¹³C and ³¹P peaks assigned to the carbonyl carbon and phosphoryl phosphine of coordinated CMPO was detected in the lower field than that of free CMPO. From these results, it was concluded that the uranyl nitrato complex with CMPO in both the states has the structure with two nitrate and one CMPO coordinated as bidentate in the equatorial plane of uranyl ion, i.e., UO₂(NO₃)₂·CMPO. Furthermore, the electrochemical studies of UO₂(NO₃)₂·CMPO complex in CH₃CN have been carried out using cyclic and normal pulse voltammetric methods. It was found that the UO₂(NO₃)₂·CMPO complex is reduced to U(V) complex at around ?1.22V vs. Fc/Fc⁺ (ferrocene/ferrocenium) and that the resulting reductant is oxidized to U(VI) at around +0.04V vs. Fc/Fc⁺.     

Luminescent monitoring of metal dititanium triphosphates as promising materials for radioactive waste confinement

The potential use of luminescent probes for control over the structural state of MTi₂(PO₄)₃ double metal phosphates as host materials for radioactive waste confinement is examined. Luminescence spectra of pure and metal (Al, In, V) and rare-earth (Pr, Sm, Dy) doped MTi₂(PO₄)₃ (M = Li, Na, K) phosphate compounds (in crystalline and related amorphous forms) under X-ray, VUV (synchrotron radiation), UV and visible light excitations are analyzed. Electronic structure and absorption spectra of NaTi₂(PO₄)₃ crystals are calculated by the full-potential LAPW method. The origin of the self and impurity emission bands of MTi₂(PO₄)₃ materials is defined. It was shown that nitrogen laser with 337.1 nm generation wavelength is the most effective excitation source for remote monitoring of incorporation of various types of waste elements into MTi₂(PO₄)₃ hosts and for control over states of these hosts during storage of radioactive waste.     

Effects of Mg-ion implantation in α-Al2O3 and α-Al2O3:Mg crystals: Electrical conductivity and electronic structure changes

Undoped and Mg-doped α-Al₂O₃ single crystals were implanted with Mg ions, with an energy of 90 keV and a fluence of 10¹⁷ ions/cm². DC electrical measurements using the four-point probe method, between 295 and 428 K, were used to characterize the electrical conductivity of the implanted area. Measurements in this temperature range indicate that the electrical conductivity after implantation is thermally activated with an activation energy of about 0.03 eV both in undoped and in reduced Mg-doped α-Al₂O₃ crystals, whereas the activation energy in oxidized Mg-doped α-Al₂O₃ crystals remains close to that before implantation. The I-V characteristics of the latter samples reveal a blocking behavior of the electrical contacts on the implanted area in contrast to the ohmic contacts observed in α-Al₂O₃ single crystals with the c-axis perpendicular to the broad face, where the Mg ions were implanted. We conclude that the enhancement in conductivity observed in the implanted regions is related to the intrinsic defects created by the implantation, rather than to the implanted Mg ions. The relationship between the oxygen vacancy concentrations at different stages of etching and the changes in the electronic structure, the chemical bonding, and the Al³⁺(2p)/O²⁻(1s) and Mg²⁺(1s)/O²⁻(1s) relative intensities was studied by X-ray Photoemission Spectroscopy.     

New Approach to the Nuclear Fuel Reprocessing in Non-acidic Aqueous Solutions

A new nuclear fuel reprocessing method based on the anodic dissolution of spent fuels in aqueous alkaline solutions (Na₂CO₃-NaHCO₃) has been proposed. Experiments of the anodic dissolution were performed by using a simulated spent fuel in a Na₂CO₃-NaHCO₃ solution. Uranyl ions produced anodically were present in the solution as stable carbonato complexes, and at the same time, most of the simulated fission products (FP) were precipitated as hydroxo or carbonate compounds. Under this condition, Cs of an alkali metal group was dissolved in the solution and precipitated by adding sodium tetraphenylborate. Uranyl ion was recovered as hydroxo compounds by adding NaOH to the solution after removing precipitates of the simulated FP. In view of waste disposal, ⁹⁹Tc having a long half-life should be removed. Precipitation behavior of Tc(VII) was examined by using Re(VII) as a simulant of Tc(VII). It was found that Re(VII) species are completely removed as a precipitate by adding tetraphenylphosphonium chloride. A large amount of Na used in the present method was recovered as NaHCO₃ by blowing CO₂ into alkaline solutions. As a result, it was clarified that the proposed method is fundamentally possible as a new reprocessing method.     

Protective Oxide Film on Alloy X750 Formed in Air at 973 K

An effective pre-oxidation method for Alloy X750 was developed to reduce general corrosion in an oxygenated aqueous environment such as in BWR core water. The optimum condition of preoxidation in air at elevated temperatures was found to be 5–20 h at 973 K by considering the allowance condition of heat treatment for age-hardening.

Some characteristics of the corroded oxide film have been clarified by surface analyses with XMA, SIMS, AES, XPS etc. The film was composed of double oxide layers, namely a highly crystallized NiFe₂O₄ outer layer and a high Cr₂O₃ content inner layer. The passive property of the film has been recognized to be due to the nature of the oxides whereby NiFe₂O₄ restricts the dissolution of metals because of its low solubility and Cr₂O₃ restricts the diffusion of metal ions because of its high binding energy and low diffusion coefficient.     

Temperature effect study of silicon-on-insulator structures prepared by high dose implantation of nitrogen

The temperature effect on the microstructure of the N⁺-ion implantation-induced Si₃N₄ buried layer was investigated. The underlying silicon nitride layers were formed in a Si (1 1 1) wafer after implantation of 50 keV nitrogen ions (fluence: 1 × 10¹⁷, 2 × 10¹⁷ and 5 × 10¹⁷ ions/cm²). It was observed that a continuous amorphous layer of about 200 nm thickness was formed in all implanted samples due to the irradiation damage. After 30 min annealing at 900 °C, poly-crystalline Si₃N₄ products were found by TEM examination in the specimen implanted with 5 × 10¹⁷ ions/cm² dose. In the case of annealing at 1200 °C a continuous single-crystalline α-Si₃N₄ buried layer was formed indicating that the amorphous layer in the implanted samples could be transformed into three successive layers, which are amorphous SiO₂, single-crystal α-Si₃N₄ and retained defects from surface to inner substrate, respectively.     

Boiling and drying accident of high-level liquid waste in a reprocessing plant: Examination of the NO2 and NO generation using the simulated waste

ABSTRACT

NO₂ and NO generated during a boiling and drying accident, which affects the release of volatilized radioactive Ru into the atmosphere, were examined using various samples including simulated high-level liquid waste and a thermogravimetric analyzer. NO₂ and NO in the gas flowing out of the analyzer were measured separately using a NOx analyzer equipped with NO₂ and NO sensors. The samples were heated to 600°C at constant heating rates of mainly 0.2 and 1°C min^?1 that was adopted taking into account the decay heat of high-level liquid waste. It was found that under 180°C some nitrates in the liquid waste mainly separated their nitrate groups as HNO₃ without generating NOx (a mixture of NO and NO₂) and above 300°C the residual HNO₃ in the waste participated in thermal decomposition generating NOx. The generation rates of NO₂ and NO were obtained as a function of time using Arrhenius type equations, and the O₂ rate was derived from these equations using the stoichiometry of the reactions that generate NO₂, NO, and O₂.     

LiMgPO4:Tb,B - A new sensitive OSL phosphor for dosimetry

Optically Stimulated Luminescence (OSL) technique has emerged as a serious competitor to Thermally Stimulated Luminescence (TSL) technique in various dosimetric applications, especially after the development of crystalline alumina (Al₂O₃:C) doped with carbon. Since then, several attempts are being made to develop other possible materials for OSL based dosimetric applications. Efforts conducted in our laboratory in this direction have led to the development of a new phosphor, Lithium Magnesium Phosphate doped with terbium and boron (LiMgPO₄:Tb,B). This phosphor is prepared by solid-state diffusion method involving conventional air furnaces with operating temperature 1000 °C and easily amenable to large scale production without compromising primary dosimetric advantages. In this work we present some of the dosimetric OSL characteristics of this phosphor. The phosphor exhibits a main TSL peak at 250 °C. The phosphor also emits OSL, when the irradiated phosphor is stimulated with 470 nm light with the OSL sensitivity 1.3 times that of commercially available Al₂O₃:C. Photoluminescence (PL) emission spectrum consists of sharp lines characteristics of Tb³⁺ emission. The OSL discs made out of this phosphor are reusable up to at least 50 cycles, the phosphor exhibits dose linearity up to 1 kGy. Minimum detectable dose is found to be 20 μGy and fading of the OSL signal is found to be about 16% in four days, after which the OSL signal stabilizes.