Molecular-sieving effect of zeolite 3A on adsorption of H2, HD and D2

Synthetic zeolite 3A has the molecular-sieving windows of nominal diameter 0.3 nm in its crystal lattice framework, which obstruct the crystalline adsorption of molecules of diameter larger than 0.3 nm, except water, hydrogen and helium. The window's diameter slightly varies with temperature, however, that is endorsed in experimental results that hydrogen cannot be adsorbed at the liquid-nitrogen temperature. Authors measured the range of temperature where zeolite 3A permits hydrogen adsorption, and revealed the temperature difference of several degrees in appearance of molecular sieving for H₂ and D₂. This difference is important because from a H₂–D₂ mixture one isotope could be isolated by adsorption if operated at a temperature regulated between the molecular-sieving appearance temperatures. We have reported large values of D₂/H₂ separation factor obtained from molecular-sieving experiments. In this study, the effect of sieving for the hybrid-atomic isotope HD is examined using a H₂–HD–D₂ mixture. We here report the experimental HD/H₂ separation factor evaluated between the D₂/H₂ factor and unity. This result is significant because where the effective molecular diameter concerning the sieving mechanism is suggested. From this knowledge, the isotopic effect of sieving for HT and DT can be predicted.     

多巴胺D2受体显像剂Epidepride的合成及其^131I标记

以3－甲氧基水杨酸为原料合成了Epidepride[S-(-)-N-[1-乙基－2－吡咯烷基]-5－碘－2,3－二甲氧基基甲酰胺]及其标记前体（S－（－）－5－（三正丁基锡）－N（1－乙基－2－吡咯烷基）甲基]2,3-二甲氧基苯甲酸酰胺）,并采用双氧水法对标记前体进行^131I标记,获得了^131I-epidepride,标记率和放化纯度均大于95％。132I-epidepride溶液体外稳定性好,4℃放置15d放化纯度仍大于90％。^131I-epidepride与D2受体亲和力高,大鼠脑内纹状体与小脑的摄取比在320min时高达237;在脑内纹状体的吸收可被Spiperone安全阻断。因此,^131I－epideride有望成为多巴胺D2受体SPECT显像剂。     

Thermophysical properties of NpO2, AmO2 and CmO2

The information on thermal and mechanical properties of the minor actinide dioxides: NpO₂, AmO₂ and CmO₂, is still very scarce, and a large uncertainty exists because of difficulties related to their fabrication and manipulation. Prognosis based on a set of the sound physical models and the similarity principle can be useful in this situation. Using the combination of the macroscopic and microscopic approaches developed earlier for thermodynamic properties of actinide dioxides, and the Klemmens model for their thermal conductivity, a few relationships bounding the main thermophysical properties of the actinide dioxides were deduced. These relationships were applied for the calculation of the isochoric and isobaric heat capacity, the isobaric thermal expansion coefficient, the isothermal bulk elastic modulus and the thermal conductivity of NpO₂, AmO₂ and CmO₂ in a large temperature range. A rather satisfactory agreement with the available experimental data and recommendations was demonstrated.     

用^125—I—β—CIT与^125I—IBZM体内放射自显影研究MPTP致帕金森病小鼠中枢多巴胺转运蛋白与受体变化

应用     

Vacuum plasma etching of 1 wt% La2O3 dispersed tungsten

Vacuum plasma etching of 1 wt% La₂O₃ doped tungsten alloy surfaces were carried out to refine the surface morphology for enhancing its bonding characteristics with copper for fusion reactor components. Three different gas compositions containing argon with zero, 14.3 and 25 vol% hydrogen were used to carry out the plasma etching from 30 to 120 s on the given samples. Mitutoyo surface roughness (R_a) measurement, FORM TALYSURF and scanning electron microscopy (SEM) were employed to measure the changes in the surface roughness. Plasma etching with 14.3 vol% hydrogen mixture was found to be the best in micro-roughening the alloy surface. The maximum increase of 44% in R_a value was obtained with this gas mixture, when etched for 90 s.     

Reduction of UO2 by H2

The reactivity of H₂ towards UO₂²⁺ has been studied experimentally using a PEEK coated autoclave where the UO₂²⁺ concentration in aqueous solution containing 2 mM carbonate was measured as a function of time at p_H2∼40 bar. The experiments were performed in the temperature interval 74-100 °C. In addition, the suggested catalytic activity of UO₂ on the reduction of UO₂²⁺ by H₂ was investigated. The results clearly show that H₂ is capable of reducing UO₂²⁺ to UO₂ without the presence of a catalyst. The reaction is of first order with respect to UO₂²⁺. The activation energy for the process is 130 ± 24 kJ mol⁻¹ and the rate constant is k_298K=3.6×10⁻⁹ l mol⁻¹ s⁻¹. The activation enthalpy and entropy for the process was determined to 126 kJ mol⁻¹ and 16.5 J mol⁻¹ K⁻¹, respectively. Traces of oxygen were shown to inhibit the reduction process. Hence, the suggested catalytic activity of freshly precipitated UO₂ on the reduction of UO₂²⁺ by H₂ could not be confirmed.     

HfO2 and Ta2O5 as grain growth inhibitors in Eu2O3

Because of the high neutron capture cross section for five consecutive europium isotopes, Eu₂O₃ is of interest as a control material for nuclear reactors. A tendency toward excessive grain growth degrades its mechanical properties. Small amounts of HfO₂ and Ta₂O₅ were added to the Eu₂O₃ in attempts to suppress this grain growth. Three at % substitution of Hf for     

Radiotoxicity hazard of U-free PuO2+ZrO2 and PuO2+ThO2 spent fuels in LWR

The radiotoxicity hazard of U-free Rock-like oxide: ROX (PuO₂+ZrO₂) and Thorium oxide: TOX (PuO₂+ThO₂) LWR spent fuels is investigated and radiotoxicity hazard of MOX spent fuel is considered as a reference case. The long-term ingestion radiotoxicity hazard of ROX spent fuel is one third and nearly one fourth of that of TOX and MOX spent fuels, respectively. This is because the discharged Pu and long lived Np in ROX fuel is less than that of TOX and MOX fuels. In TOX fuel, discharged Pu and MA are lower than that of MOX fuel but the long-term radiotoxicity hazard of spent fuel is nearly the same as MOX spent fuel. At the cooling 10⁵ years, the radiotoxicity hazard of TOX spent fuel is approximately ten and three times higher than that of ROX and MOX spent fuels, respectively due to higher toxic contribution of ²²⁹Th in TOX spent fuel.     

Formation of U2C3 in the reaction of UC2 with UO2

The formation of U₂C₃ by the reaction of UC₂ with UO₂ has been studied by chemical and X-ray analyses at temperatures between 1400 and 1700 °C in vacuo. The reaction is represented by 7 UC₂ + UO₂ → 4 U₂C₃ + 2 CO.     

Characterization and densification studies on ThO2-UO2 pellets derived from ThO2 and U3O8 powders

ThO₂ containing around 2-3% ²³³UO₂ is the proposed fuel for the forthcoming Indian Advanced Heavy Water Reactor (AHWR). This fuel is prepared by powder metallurgy technique using ThO₂ and U₃O₈ powders as the starting material. The densification behaviour of the fuel was evaluated using a high temperature dilatometer in four different atmospheres Ar, Ar-8%H₂, CO₂ and air. Air was found to be the best medium for sintering among them. For Ar and Ar-8%H₂ atmospheres, the former gave a slightly higher densification. Thermogravimetric studies carried out on ThO₂-2%U₃O₈ granules in air showed a continuous decrease in weight up to 1500 °C. The effectiveness of U₃O₈ in enhancing the sintering of ThO₂ has been established.     

Optical properties of UO2 and PuO2

We perform first-principles calculations of electronic structure and optical properties for UO₂ and PuO₂ based on the density functional theory using the generalized gradient approximation (GGA) + U scheme. The main features in orbital-resolved partial density of states for occupied f and p orbitals, unoccupied d orbitals, and related gaps are well reproduced compared to experimental observations. Based on the satisfactory ground-state electronic structure calculations, the dynamical dielectric function and related optical spectra, i.e., the reflectivity, adsorption coefficient, energy-loss, and refractive index spectrum, are obtained. These results are consistent with the available experiments.     

High-temperature specific heat of UO2 ThO2, and A12O3

The high-temperature specific heat of solid UO₂, ThO₂, and Al₂O₃ can be represented by an equation of the form $\text{C}{}_{\mathrm{p(s)}}\text{= 3}{}_{\mathrm{n}}\text{RF(?}{}_{\mathrm{D}}\text{/T) + dT}{}^3$, (1) where ?_D is the Debye temperature, F(?_D/T) is the Debye function, $\text{d}$ represents contributions of the anharmonic vibrations within the lattice, and $\text{n}$ denotes the number of atoms per molecule. In the liquid the corresponding equation is $\text{C}{}_{\mathrm{p(1)}}\text{= 3}{}_{\mathrm{n}}\text{RF(?}{}_{\mathrm{D}}\text{/T) +}\text{h}\text{T}{}^2$, (2) where h is the anharmonic term. It is shown that for Al₂O₃ and UO₂, where experimental data for the liquid phase are also available, $\text{d}\text{h}$ has the same value, Indicating that both materials behave identically. If we compare the thermodynamic relationship $\text{C}{}_{\mathrm{p}}\text{? C}{}_{\mathrm{v}}\text{= Vα}{}^2\text{KT}$, (3) where V is the volume, $\text{α}$ the volume expansion coefficient, and $\text{K}$ the bulk modulus, with equation (1), It follows that d must be equal to $\text{Vα}{}^2\text{K}\text{T}{}^2$; the value of $\text{Vα}{}^2\text{K}\text{T}{}^2$ is calculated in the temperature region where d was obtained; within experimental error they are equal.     

Thermophysical studies on the binary system UO2(NO3)2·6H2O - Sr(NO3)2

Thermoanalytical (TG-DTA-EGA) and X-ray diffraction measurements have been used to study the reaction between uranyl nitrate hexahydrate and strontium nitrate. The results confirmed the absence of a direct interaction between the two compounds. The presence of strontium nitrate, however, ensured that the extent of hydrolysis and polymerisation of uranyl nitrate hexahydrate during its dehydration and decomposition to UO₃ is significantly reduced. DTA curves recorded in both heating and cooling modes gave evidence to the occurrence of a reaction between molten strontium nitrate and uranium trioxide to form nitrato-complexes of uranium and strontium. X-ray diffraction data on reaction residues obtained at different temperatures and cooled to room temperature also showed evidence for the formation of such complexes. The results obtained indicated an increase in thermal stability of these nitrato-complexes with increase in Sr/U ratio. The complex with an Sr/U ratio of 2.0 is stable up to 660 °C and the complex with Sr/U ratio of 4.0 is stable up to 680 °C. These complexes decompose at higher temperatures to give strontium uranates.     

掺杂Cr2O3对UO2芯块烧结行为的影响

提高燃料燃耗的一个有效手段是通过增大UO₂晶粒尺寸来减少元件内部气体压力,在大晶粒UO₂芯块中,裂变气体到达晶界表面的距离增加,因而裂变气体的释放速率降低,元件内部气体压力的增高缓慢。本文研究了添加Cr₂O₃对UO₂晶粒尺寸的影响。对纯UO₂、添加0.5% Cr₂O₃及5% Cr₂O₃ 3种配方的芯块进行了试验,在5%H₂Ar保护下,以10 ℃/min和5 ℃/min的升温速率升温至1 700 ℃,然后烧结2 h或4 h,对比纯UO₂芯块与添加Cr₂O₃的芯块发现,添加Cr₂O₃可有效增大晶粒尺寸;较长的烧结时间可促进晶粒长大;较低的升温速率也使晶粒长大。烧结过程产生液相烧结,液相浸润晶粒边界,促进晶粒长大。     

LiErO2 formation on Er2O3 in static and natural convection lithium

Er₂O₃ is candidate material for insulating coating to prevent the magnetohydrodynamic (MHD) pressure drop in the self-cooled liquid Li blanket system. Although Er₂O₃ is stable material, detailed chemical behavior in liquid Li is not clear. Corrosion behavior of bulk Er₂O₃ in Li is investigated in static and flowing condition in the present study. After these tests, good compatibility of Er₂O₃ was confirmed and slight formation of LiErO₂ was detected by XRD analysis. This chemical behavior did not change in a static and flowing tests, however some of the corrosion product of LiErO₂ was removed easily by the Li flow. Intensity of LiErO₂ peaks in XRD spectrum suggests that the temperature gradient may affect the reaction rate in the natural convection loop. Since corrosion rate of Er₂O₃ is very small, slight change in state will be important information to evaluate lifetime of coating.     

Molecular dynamics simulations of C2, C2H, C2H2, C2H3, C2H4, C2H5, and C2H6 bombardment of diamond (1 1 1) surfaces

The sticking and erosion of C₂H_x molecules (where x=0-6), at 300 and 2100 K onto hydrogenated diamond (1 1 1) surfaces was investigated by means of molecular dynamics simulations. We employed both quantum-mechanical and empirical force models. Generally, the sticking probability is observed to somewhat increase when the radical temperature increases and strongly decrease with increasing number of H atoms in the molecule.     

On the effect of TiO2 additions on sintering of UO2

Small additions of TiO₂ are known to increase the density of sintered UO₂. It is shown that this effect coincides with an increase in the diffusion rate of the slower moving ion, the uranium ion. Quantitative metallography and measurement of the gas release following high-dose ion-bombardment show that small amounts of titanium are soluble in UO₂. Possible mechanisms by which TiO₂ affects the disorder of UO₂ are discussed. Reduction of TiO₂ and interstitial solution of the small titanium ions are favoured. Similar experiments are reported for ThO₂+TiO₂.     

One-Dimensional Fluid Model of Pulse Modulated Radio-Frequency SiH4 /N2 /O2 Discharge

Driven by pulse modulated radio-frequency source,the behavior of SiH 4 /N 2 /O 2 plasma in capacitively coupled discharge are studied by using a one-dimensional fluid model.Totally,48 different species(electrons,ions,neutrals,radicals and excited species) are involved in this simulation.Time evolution of the particle densities and electron temperature with different duty cycles are obtained,as well as the electronegativity n SiH3 /n e of the main negative ion(SiH3).The results show that,by reducing the duty cycle,higher electron temperature and particle density can be achieved for the same average dissipated power,and the ion energy can also be effectively reduced,which will offer evident improvement in plasma deposition processes compared with the case of continuous wave discharge.     

Kinetics of initial stage of sintering of UO2 and UO2 with Nd2O3 addition

The kinetics of initial stage sintering of UO₂ powder were reinvestigated, using Ar-10% H₂ atmosphere. The effect of the addition of neodynium oxide was studied. The results revealed that surface and grain boundary diffusion mechanisms act simultaneously. The values of activation energies were found to be $\text{48.48 ± 3.51 kcal/mole}$ in the temperature range 870–942°C and $\text{89.88 ± 9.87 kcal/mole}$ in the temperature range of 942–1030°C for UO₂, and $\text{115.61 ± 7.77 kcal/mole}$ in the temperature range 1030–1150°C for UO₂ + Nd₂O₃. An important decrease in the calculated diffusion coefficient occurs by the addition of Nd₂O₃.