The heats of formation of UAl2, UAl3, and UAl4

Preparations of the intermetallic compounds UAl₂, UAl₃ and UAl₄ were obtained by high-temperature interdiffusion of aluminum and dispersed uranium, prepared by decomposing its hydride then grinding the product and heating the powder obtained. Debye x-radiographic investigation showed that the preparations obtained consisted of one phase and the parameters of their structures were close to those published earlier. The amount of hydrogen evolved during separate solution of the preparations and the starting components in a specially selected solvent (mixture of HCl, H₃PO₄, Na₂SiF₆, H₂PtCl₅ and CuSO₄· 5H₂O) Indicated that the preparations had the compositions; UAl_1.997, UAl_2.994 and UAl_3.997.The differences in the heats of solution of these preparations and appropriate mixtures of their components gave die heats of formation (–H°₂₉₃)UAl₂, UAl₃ and UAl₄, which were 22.3±2.4, 25.2±2.2 and 31.2±3.1 kcal/mole, respectively.The authors would like to thank N. T. Chebotarev and P. N. Petrov for the x-radiographic analyses of the preparations, T. S. Men'shikova for the metallographic investigation and L. M. Kopytin for his valuable advice and interest in the work.     

A M(o)ssbauer study of iron/polytetrafluoroethylene nanocomposites prepared by high-energy ball milling

Iron/polytetrafluoroethylene (Fe/PrFE) nanocomposites were prepared by means of high-energy ball milling for different lengths of time. Three new components of FeF2, FeF3, and Fe3C in the resultants were mainly investigated using the M(o)ssbauer spectroscopy (MS). The components and average grain size of the nanocomposites were also measured using X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively.     

Characterization of monazite glass-ceramics as wasteform for simulated α-HLLW

Two monazite glass-ceramic wasteforms were sintered by mixing the lanthanum metaphosphate glass powder with the oxide powder of the components in simulated α-HLWs. The co-existence of components Al and Mo in an iron phosphate melt separated the melt into two immiscible glass melts, namely aluminum iron phosphate glass (Gb) and molybdenum iron phosphate glass (Gg). 24 wt% of ZrO₂, together with P₂O₅ and proper amounts of Fe and Mo formed a zirconium pyrophosphate glass (Gg1), which was immiscible with the phase Gg. The iron ions in the wasteforms were all in Fe³⁺, 1/3 of which was in 4-fold coordination. The O/P and O/(P + 1/3Fe³⁺) ratios for the glass phases were Gg1 3.70, Gb 3.89-3.98, Gg 4.23-4.25, and Gg1 3.58, Gb 3.47-3.42, Gg 3.74-3.69, respectively. The dissolution rates of two wasteforms were 0.3008 and 0.2598 g/m²d, respectively.     

A Mssbauer study of iron/polytetrafluoroethylene nanocomposites prepared by high-energy ball milling

1Introduction High-energy ball milling has been widely used for the preparation of nanostructured materials,in-cluding a variety of materials having nanosized di-mensions embedded in some ceramic or immerged matrices of metals.However,little attention has been paid to the preparation of metal–polymer nanocompo-sites by ball milling.Recently,iron fluorides have been investigated due to their simple chemical nature and various magnetic properties[1-3].In this study,the high-energy ball milling …     

Characteristics of Oxidation Reaction of Rare-earth Chlorides for Precipitation in LiCl-KCl Molten Salt by Oxygen Sparging

The precipitation reaction of some rare earth chlorides (La/Ce/Nd/GdCl3) in a LiCl-KCl molten salt has been carried out by using the oxygen sparging method. In this study, regardless of the oxygen sparging time and the molten salt temperature, oxychlorides (REOCl) for LaCl₃, NdCl₃ and GdCl₃, and an oxide (REO₂) for CeCl₃ are formed as a precipitate. The conversion of rare-earth chlorides into insoluble precipitates was described by using a conversion ratio. The conversion ratio increased exponentially with the oxygen sparging time and finally showed asymptotic value at 1,023 K of the molten salt temperature condition. The conversion ratios of LaCl₃, NdCl₃ and GdCl₃ were increased with the molten salt temperature, however, even though the conversion ratio was increased from 0.660 to 0.995 with increasing molten salt temperature from 823 to 923 K at 60 min of a sparging time, the values of the conversion ratio of CeCl₃ were nearly constant (over 0.999) with the molten salt temperature. As a result of the thermogravimetric analysis of the precipitates (oxychlorides), about 11–13% of a weight loss happened in the case of LaOCl, NdOCl and GdOCl, and all the oxychlorides were converted to their oxides i.e. La₂O₃, Nd₂O₃ and Gd₂O₃ at a high temperature and oxygen atmosphere.     

Low-temperature immobilization of actinides and other components of high-level waste in magnesium potassium phosphate matrices

The magnesium potassium phosphate (MPP) matrices formed by the room-temperature reaction of MgO and KH₂PO₄ solution were used for immobilization of simulated liquid alkaline high-level waste (HLW) containing actinides, fission and corrosion products. Novel procedures of solidification of HLW simulants were developed to increase stability of the MPP matrices to leaching radionuclides (Pu, Np, Am, Cs, Sr, Tc, I and Se), matrix-forming (K, Mg and PO₄) and admixture components (NO₃, NO₂, Na and others) as well as hazardous elements (Pb, Cr, Zn and others) according to the ANS, PCT, TCLP standards. Density (∼1.7 g/cm³), compressive strength (>20 MPa), radiation resistance of the matrices and chemical yield of radiolytic hydrogen (0.004 molecule H₂/100 eV) were determined. The phase composition of the matrices and distribution of radionuclides were studied by XRD and autoradiography correspondingly.     

Fracture toughness of welded joints materials for main pipelines at Ignalina NPP

This paper deals with an investigation of mechanical and fracture toughness characteristics of welded joint materials used in Ignalina Nuclear Power Plant (NPP) reactor main circulating circuit (MCC) and steam pipelines. Basic metal of MCC group distributing header (GDH) steel 08Ch18N10T (Du-300), its weld metal welded by manual and automatic arc method using the wire SV-04Ch19N11M3 and electrodes EA-100/10U or EA-100/10T, this joint heat-affected zone metal and base metal of the main steam system—steel 16GS (DU-630) and its weld metal welded by manual arc method using the wire SV-08GS2 and electrodes UONI-13/55 were tested.Mechanical properties of welded joints materials—proportional limit (σ_pl), yield (σ_y) and ultimate (σ_u) strength, fracture stress (σ_f) and ductility (Z) (percent reduction of area) of the specimens were determined. Investigation of relative critical stress intensity factor for fixed thickness of the specimen and critical J-integral, J_IC, was performed.The probabilistic investigation of influence of the mechanical properties (σ_pl, σ_y, σ_u) onto fracture toughness characteristics and J_IC for tested materials by using linear regression model with three independent variables was performed.Research enabled to conclude that proposed multivariable regression model with 80% probability (confidence coefficient α = 0.05) has explained reasonably well the dependence of with σ_pl, σ_y, σ_u and it has shown the non-acceptability of probabilistic evaluation of the model with respect to J_IC.     

Solubility studies,thermodynamics and electrical conductivity in the Th1−xSrxO2 system

A polymeric gel combustion method was employed for the lower temperature synthesis of 1, 2, 3, 5, 7.5, 10 and 15 mol.% SrO doped ThO₂ solid solutions. After final sintering of these samples at 1573 K in Ar, the solubility limit was found to be 1 mol.%, giving rise to a composition-independent value of (559.84±0.02) pm (at 300 K) for the CaF₂-type unit cell. AC impedance measurements carried out on discs of 1, 2, 3 and 5 mol.% SrO in ThO₂ discs in flowing Ar, yielded values of 116, 115, 128 and 96 kJ/mol, respectively as the activation energies for the bulk ionic conductivity. The thermodynamic activities of SrO in the 1, 2 and 3 mol.% solid solutions were measured using [SrO]_ThO2,SrF₂,O₂,Pt as the test electrodes and SrZrO₃,ZrO₂,SrF₂,O₂,Pt as the reference with sintered SrF₂ as the electrolyte over the range of approximately 650–800 K. The activity values differed marginally from each other, but were indicative of the combined (and not free) state of SrO. Hence, only a limiting value of a_SrO for the just saturated (mole fraction of SrO=0.01) thoria solid solution could be derived as log a_SrO=0.36−4602/T (K).     

Large third-order optical nonlinearity of silver colloids in silica glasses synthesized by ion implantation

Silver ion implantations in fused silica glasses have been made to synthesize silver nanocluster-glass composites and a combination of ‘Anti-Resonant Interferometric Nonlinear Spectroscopy (ARINS)’ and ‘Z-scan’ techniques has been employed for the measurement of the third-order optical susceptibility of these nanocomposites. The ARINS technique utilizes the dressing of two unequal-intensity counter-propagating pulsed optical beams with differential nonlinear phases, which occurs upon traversing the sample. This difference in phase manifests itself in the intensity-dependent transmission, measurement of which enables us to extract the values of nonlinear refractive index (η₂) and nonlinear absorption coefficient (β), finally yielding the real and imaginary parts of the third-order dielectric susceptibility (χ⁽³⁾). The real and imaginary parts of χ⁽³⁾ are obtained in the orders of 10⁻¹⁰ e.s.u for silver nanocluster-glass composites. The present value of χ⁽³⁾, to our knowledge, is extremely accurate and much more reliable compared to the values previously obtained by other workers for similar silver-glass nanocomposites using only Z-scan technique. Optical nonlinearity has been explained to be due to two-photon absorption in the present nanocomposite glasses and is essentially of electronic origin.     

Reactivity temperature coefficients for the HEU and LEU fuel of the MNSR reactor

Analysis of the Reactivity Temperature Coefficients of the Miniature Neutron Source Reactor (MNSR) for normal and accidental conditions (above 45 °C) using HEU-UAl₄ and the LEU: U₃Si, U₃Si₂ and U9Mo fuel were carried out in this paper. The Fuel Temperature Coefficient (FTC), Moderator Temperature Coefficient (MTC), and Moderator Density Coefficient (MDC) were calculated using the GETERA code. The contribution of each isotope presented in the fuel cell was calculated for the temperature range of 20 °C–100 °C at the beginning of the core life. The average values of the FTC for the UAl₄, U₃Si, U₃Si₂ and U9Mo were found to be: −2.23E-03, −1.85E-02, −1.96E-02, −1.85E-02 mk/°C respectively. The average values of the MTC for the UAl₄, U₃Si, U₃Si₂ and U9Mo were observed to be: −8.91E-03, −1.24E-04, −4.70E-03, 2.10E-03 mk/°C respectively. Finally, the average values of the MDC for the UAl₄, U₃Si, U₃Si₂ and U9Mo were observed to be: −2.06E-01, −2.03E-01, −2.04E-01, −2.03E-01 mk/°C respectively. It's found also that the dominant reactivity coefficient for all types of fuel is the MDC.     

Effect of nitrate on corrosion of austenitic stainless steel in boiling nitric acid solution containing chromium ions

The oxidation behavior of chromium and the corrosion behavior of austenitic stainless steel in boiling nitric acid solution containing highly concentrated nitrates were investigated using UV-visible spectroscopic measurements, Raman spectral measurements, immersion tests, and potentiodynamic polarization measurements. The oxidation rate measurement of chromium from Cr(III) to Cr(VI) was performed by 1 M boiling nitric acid solution containing each highly concentrated nitrates: Al(NO₃)₃, Nd(NO₃)₃, Ca(NO₃)₂, Mg(NO₃)₂, and NaNO₃ as a simulant of uranium nitrate in uranium concentrator in reprocessing plants. As a result, the rate of chromium oxidation was different depending on the added nitrates even at the same nitric acid concentration. In addition, the oxidation rate of chromium was increased with increasing the calculated partial pressure of nitric acid in consideration of the hydration of cation of nitrates. Furthermore, the corrosion rate of type 310 stainless steel was accelerated by the solution having a high chromium oxidation rate containing nitrates. These results indicated that the acceleration of the corrosion rate in the solutions depending on the oxidation rate of chromium, and the rate is affected by the salt-effect of nitrates.     

H310BO3/ZnS(Ag)热中子闪烁体转换屏的涂布法制备及性能研究

本文采用涂布法制备了一系列H₃¹⁰BO₃/ZnS(Ag)闪烁体转换屏样品,对其成分配比进行了优化。结果表明,最佳的H₃¹⁰BO₃/ZnS(Ag)质量比在1∶6~1∶7之间,最佳的黏合剂用量为总质量的25%。利用中子照相设备对转换屏的发光均匀性进行了成像分析,结果显示光输出非常均匀;对楔形镉条进行中子成像,并采用调制传递函数(modulation transfer function,MTF)方法计算了系统分辨率,结果显示,在MTF值为0.1时,对于厚度分别为270(11)、350(14)、404(9)及505(15)μm的转换屏,其相应的系统空间分辨率分别为255.6、315.9、371.0和471.3 μm。     

Study of XeF2 fluorination potential against SrO,MoO3, and Nb2O5 in TG/DTA for use in reactive gas recycle

Oxides SrO, MoO₃, and Nb₂O₅, simulating parts of the Used Nuclear Fuel (UNF) matrix were fluorinated using XeF₂ to form volatile and non-volatile compounds to demonstrate the possibility of a chemical and thermal separations. Experiments were conducted using a TG/DTA instrument at the milligram quantity scale, and XRD enabled confirmation for the fluorination reaction when sample residues were present. The study of these chemistries could be incorporated into advanced separations methods to provide another possible solution for the long-term, sustainability of nuclear power as the issue of reuse and disposal of commercial fuel continues to grow.     

Selective separation and recovery of cesium by ammonium tungstophosphate-alginate microcapsules

A fine crystalline ammonium tungstophosphate (AWP) exchanger with high selectivity towards Cs⁺ was encapsulated in biopolymer matrices (calcium alginate, CaALG). The characterization of the AWP-CaALG microcapsule was examined using SEM/WDS, IR and DTA/TG analyses, and the selective separation and recovery of ¹³⁷Cs were examined by the batch and column methods using simulated (SHLLW) and real high-level liquid waste (HLLW). The free energy (ΔG°) of the ion exchange (NH₄⁺ ↔ Cs⁺) for fine AWP crystals was determined at −13.2 kJ/mol, indicating the high selectivity of AWP towards Cs⁺. Spherical and elastic AWP-CaALG microcapsules (∼700 μm in diameter) were obtained and fine AWP crystals were uniformly immobilized in alginate matrices. Relatively large K_d values of Cs⁺ above 10⁵ cm³/g were obtained in the presence of 10⁻³–1 M Ca(NO₃)₂, resulting in a separation factor of Cs/Rb exceeding 10². The irradiated samples (⁶⁰Co, 17.6 kGy) also exhibited large K_d values exceeding 10⁵ cm³/g in the presence of 2.5 M HNO₃. The K_d values in the presence of 0.1–9 M HNO₃ for 67 elements were determined and the order of K_d value was Cs⁺ ? Rb⁺ > Ag⁺. The breakthrough curve of Cs⁺ had an S-shaped profile, and the breakpoint increased with decreasing flow rate; the breakpoint and breakthrough capacity at a flow rate of 0.35 cm³/min for the column (0.7 g AWP-CaALG) were estimated at 25.2 cm³ and 0.068 mmol/g, respectively. Good breakthrough and elution properties were retained even after thrice-repeated runs. The uptake (%) of Cs⁺ in SHLLW (28 metal components-1.92 M HNO₃, SW-11, JAEA) was estimated at 97%, and the distribution of Cs⁺ and Zr/Ru into the AWP and alginate phases, respectively, were observed by WDS analysis. Further, the selective uptake of ¹³⁷Cs exceeding 99% was confirmed by using real HLLW (FBR “JOYO”, JAEA). AWP-CaALG microcapsules are thus effective for the selective separation and recovery of Cs⁺ from HLLWs.     

Corrosion behavior of Ni-based structural materials for electrolytic reduction in lithium molten salt

In this study, the corrosion behavior of new Ni-based structural materials was studied for electrolytic reduction after exposure to LiCl-Li₂O molten salt at 650 °C for 24-216 h under an oxidizing atmosphere. The new alloys with Ni, Cr, Al, Si, and Nb as the major components were melted at 1700 °C under an inert atmosphere. The melt was poured into a preheated metallic mold to prepare an as-cast alloy. The corrosion products and fine structures of the corroded specimens were characterized by scanning electron microscope (SEM), Energy Dispersive X-ray Spectroscope (EDS), and X-ray diffraction (XRD). The corrosion products of as cast and heat treated low Si/high Ti alloys were Cr₂O₃, NiCr₂O₄, Ni, NiO, and (Al,Nb,Ti)O₂; those of as cast and heat treated high Si/low Ti alloys were Cr₂O₃, NiCr₂O₄, Ni, and NiO. The corrosion layers of as cast and heat treated low Si/high Ti alloys were continuous and dense. However, those of as cast and heat treated high Si/low Ti alloys were discontinuous and cracked. Heat treated low Si/high Ti alloy showed the highest corrosion resistance among the examined alloys. The superior corrosion resistance of the heat treated low Si/high Ti alloy was attributed to the addition of an appropriate amount of Si, and the metallurgical evaluations were performed systematically.     

High Resolution Measurements of Double Differential (n, α) Cross Sections of 58Ni and natNi between 4.2 and 6.5 MeV Neutrons

Double differential (n, α) reaction cross sections of ⁵⁸Ni and ^natNi were measured for 4.2–6.5 MeV neutrons with energy resolution good enough to separate α-particles from the low-lying levels of residual nuclei by using a gridded ionization chamber. Angular distribution and excitation functions were derived for α₀, α₁ and α_i≥2 components (α-particles to the ground level, the 1st level and levels higher than the 2nd level, respectively). The experimental results were compared with these obtained from calculation based on Hauser-Feshbach model employing the optical potential and the level density parameters derived to reproduce the experimental values of total, (n,p) and (n,α)cross sections. The calculation showed fair agreement with the experimental data while it underestimated the (n,α)cross section above 6 MeV.     

Thermodynamic assessments of the Al–Th and Th–Zn systems

The phase diagrams of the Al–Th and Th–Zn systems have been evaluated by using the Calculation of Phase Diagrams (CALPHAD) method with the experimental data including the phase equilibria and thermodynamic properties. The Gibbs free energies of the liquid, bcc and hcp phases were described by the subregular solution model with the Redlich–Kister equation, and those of the stoichiometric compounds of the Th₂Al, Th₃Al₂, ThAl, Th₂Al₃, ThAl₂, ThAl₃, Th₂Al₇, Th₂Zn, ThZn₂, ThZn₄ and Th₂Zn₁₇ were described by the two-sublattice model. The calculated phase equilibria and thermodynamic properties are in good agreement with the experimental data.     

Thermodynamic investigation of the possibility of using uranium dioxide to obtain hydrogen and oxygen from water

The equilibrium composition in the system U–O–H at temperatures 300–3000 K is calculated using thermodynamic functions. It is shown that the decomposition of water in H₂ and O₂ can be achieved in steps: first with only hydrogen being released at 1200–1500 K and then only oxygen at 2100–2500 K. When uranium dioxide interacts with water, mainly two uranium oxides are formed – U₄O₉ and UO₃; nine gaseous components can have appreciable partial pressure: UO, UO₂, UO₃, UO₂(OH)₂, H₂O, H₂, H, OH, HO₂. Translated from Atomnaya énergiya,Vol. 106, No. 2, pp. 76–79, February, 2009.     

Kr ion irradiation study of the depleted-uranium alloys

Fuel development for the reduced enrichment research and test reactor (RERTR) program is tasked with the development of new low enrichment uranium nuclear fuels that can be employed to replace existing high enrichment uranium fuels currently used in some research reactors throughout the world. For dispersion type fuels, radiation stability of the fuel-cladding interaction product has a strong impact on fuel performance. Three depleted-uranium alloys are cast for the radiation stability studies of the fuel-cladding interaction product using Kr ion irradiation to investigate radiation damage from fission products. SEM analysis indicates the presence of the phases of interest: U(Al, Si)₃, (U, Mo)(Al, Si)₃, UMo₂Al₂₀, U₆Mo₄Al₄₃ and UAl₄. Irradiations of TEM disc samples were conducted with 500 keV Kr ions at 200 °C to ion doses up to 2.5 × 10¹⁹ ions/m² (∼10 dpa) with an Kr ion flux of 10¹⁶ ions/m²/s (∼4.0 × 10⁻³ dpa/s). Microstructural evolution of the phases relevant to fuel-cladding interaction products was investigated using transmission electron microscopy.