甲烷的氢同位素交换的热力学理论计算

应用密度泛函理论(DFT)/B3LYP/6-31G**方法计算了甲烷的氢同位素交换的各反应标准摩尔生成焓、标准摩尔生成熵、标准摩尔吉布斯自由能和平衡常数.计算结果表明,温度是影响反应热力学的重要因素,较高温度有利于甲烷的氢同位素交换,但温度太高将有较多的积炭生成,欲得到较高的转化率,需要一合适的反应温度.     

LaNi5和LaNi4.7Al0.3柱内氕氘排代模拟

假设排代过程受表面反应控制和气相中H2与D2快速达到反应平衡,建立了流速和温度恒定条件下LaNi5和LaNi4.7Al0.3柱内氕排代氘的一维数学模型。该模型基于分子碰撞理论,考虑了分离因子对氢同位素排代的影响。模型中的气-固相同位素交换几率为可变参数,其余参数使用了文献值或实验值。计算了LaNi5和LaNi4.7Al0.7柱内氕排代氘及LaNi5柱内氘排代氕过程中流出端氢同位素各组分丰度随时间的变化关系并与实验结果进行了对照。结果表明:当同位素交换几率为2.96×107时,根据数学模型获得的排代流出曲线与实验结果具有良好一致性,该模型可恰当描述金属氢化物柱内氢同位素的排代行为。     

氢同位素色谱分离柱程序升温解吸的理论研究

在物理吸附动力学和多年色谱分离氢同位素实验的基础上,针对氢同位素与5A分子筛表面的程序升温解吸过程开展了理论研究,推导了一级无再吸附、一级再吸附、二级无再吸附和二级再吸附四种条件下的解吸速率方程,并通过计算形状参数和解吸活化能对解吸过程的动力学特征加以鉴别。     

聚苯乙烯-二乙烯基苯氢氘排代的热力学计算

聚苯乙烯-二乙烯基苯(SDB)是氢同位素分离技术中气-液交换反应重要的疏水催化剂载体.用密度泛函B3P86方法和基函数6-311G进行全电子计算,获得了SDB疏水官能团分子苯乙烯的基态电子状态、基态能量、离解能和几何参数.计算了苯乙烯上H、D排代反应的焓变、熵变和吉布斯函数变化,以及反应的平衡常数和气体压力比.计算结果表明,SDB上氘排代氢的反应有可能发生,但进行的程度较低,且随着反应温度的提高,这种排代将更难进行.同时,计算表明氢氘排代更易发生在苯环上,而乙烯基上的排代相对困难.     

Pt-SDB疏水催化剂应用于氢-水同位素交换的实验研究

采用气?液逆流方式对苯乙烯-二乙烯基苯共聚物担载金属铂(Pt-SDB)疏水催化剂应用于HD(g)/H2O(l)体系的氢同位素交换进行了实验室规模的中试实验研究;;对该实验系统和Pt-SDB的催化性能作出了评价;;得出了Pt-SDB的总体积传质系数Kya值和各种工艺条件。实验结果表明:当氢气流速为0.2m/s、温度为65℃时;;Pt-SDB与亲水性金属填料按1∶4的体积比混合装柱的Kya平均值达到41.5mol·m?·s?。     

水-氢同位素液相催化交换反应过程

描述了水氢同位素液相催化交换反应的模型,并从动力学和反应过程的角度对模型进行了实验验证。验证结果表明:水氢同位素液相催化交换是一个较复杂的传质反应的串联过程,主要包括汽液相间转化和氢同位素催化交换两个反应。     

氢同位素的交换与置换

固体表面吸附的氢同位素具有自发与气相氢同位素交换并达到某种程度平衡的性质,这种交换作用在金属氢化物表面同样存在.由于金属氢化物体系一般具有氢同位素效应,使得交换平衡时气-固相间的同位素丰度发生变化.利用这种性质可以进行金属氢化物柱内氢同位素间的置换,实现工程方面的应用.     

钯在氢同位素分离和纯化工艺中的应用

在迄今所知的金属-氢体系中，钯氢体系的同位素效应最强，因此，钯被广泛用于氢同位素处理工艺中。文章简述了钯氢体系的同位素效应，综述了钯及其合金在氢同位素分离和纯化工艺中的主要应用及其发展。     

水-氢交换氢同位素体系HD/H_2O、DT/D_2O和HT/H_2O分离性能模拟研究

计算模拟应用于氢同位素分离领域,能够方便、快捷地进行工艺条件分析。本工作采用数值模拟的方法对比研究了水-氢催化交换过程中HD/H_2O、DT/D2O和HT/H_2O三种氢同位素体系的分离性能。研究表明:在一定工艺条件下,三种体系均在操作温度为343K时达到最大的分离效果;随着气液比从1.0增大到3.0,最优操作温度均从343K降低到323K,但是在此过程中,HT/H_2O体系的分离效果受温度的影响较小一些;在达到最大分离效果的目标下,HT/H_2O体系需要的理论塔板数比HD/H_2O和DT/D2O体系少,同时,在优化的工艺条件下,三体系气相中氢同位素浓度在交换柱内分布曲线存在一定的差异。     

超大容量氢同位素色谱分离系统的概念设计

在多年从事色谱分离氢同位素技术研究的基础上,设计了一套超大容量氢同位素分离系统,包括系统的总体设计,以配气及纯化、三级色谱柱、气体流路及自动控制和载气回收为主的单元设计,以及调试实验方案设计。该系统的特点是可以根据氢同位素分离解吸谱图的信息比较直接地计算出解吸过程的动力学参数,即在实验数据的支持和适当的假设条件（平衡再吸附、均匀表面）下,依靠解吸速率方程、形状参数和解吸活化能的计算便可比较系统地描述其复杂的动力学过程。在以前的工作中,虽然已经证实了采用5A分子筛柱在77 K的低温下,可以连续富集氢 氘混合气中的氘、天然氢中的氘,甚至含氚重水中的氚的可行性,但本工作仅是初步的概念设计,其可行性还须通过实验结果来验证。     

Simulation of Cryogenic Rectification of Tritium-Containing Isotopic Hydrogen Mixtures

A method is presented for calculating the basic technological parameters of rectification systems for separating tritium-containing mixtures of hydrogen isotopes with intermediate homomolecular isotopic exchange stages. The method of independent determination of the concentrations was used in simulating the rectification process. The liquid-vapor equilibrium problem was solved with a correction for the nonideality of the mixtures. Heat release due to tritium decay is taken into account in the heat balance equations. The quantum-statistical method was used to calculate the equilibrium constants for simulating the homomolecular isotopic exchange. The CRYDIST computer code implementing this method is used to determine the optimal parameters of the apparatus for separative processing of two isotopic mixtures with different composition and including two low-temperature rectification columns and two homomolecular isotopic exchange units.     

Fusion-Driven Transmutation of Fission Product Cesium in its Elemental Form

Assuming fission reaction as a dominant energy source for a long-term perspective, the goal of transmutation of fission products is to cut their increasing accumulation and to keep their inventories at easily manageable level. Opposite to relatively short-lived ¹³⁷Cs (T_1/2=30yr) whose natural decay converge equilibrium mass to the level of order of 11 per GW of fission energy, an approach to similar equilibrium inventory for long- lived ¹³⁵Cs (T_1/2=2.3×10⁶ yr) requires artificial transmutation that preassumes its isotopic separation in the most studies. The present paper addresses cesium transmutation without preliminary isotope separation that means an approach to equilibrium for all the isotopes including stable ¹³³Cs. A high-flux blanket driven by Fusion Neutron Source with ITER-like parameters is proposed to transmute cesium in the elemental form. Transmutation efficiency is estimated in terms of equilibrium inventory and characteristic time to reach equilibrium both governed by the mean life-time of nuclides in transmuter. The analytical results show that the mean life-time of the target isotope ¹³⁵ Cs is as short as 21 yr which is in more than order of magnitude shorter than achieved in advanced fission reactors. It reveals that one Fusion Neutron Source with ITER-like parameters could transmute elemental cesium from 23 PWRs, the fraction of power associated with transmutation being as small as 3%.     

Isotope Effects in Electrolytic Formation of Lithium Amalgam

Isotope effects in the lithium amalgam formation were studied by using the mercury cathode and LiOH solutions. The electrolyses were carried out at different conditions of both applied voltages 4–10 V, and the concentrations of initially charged LiOH, 0.5–5 mol/dm³. Higher efficiency of electrolytic amalgam formation was observed at higher LiOH concentrations and higher applied voltages. At these conditions, however, significant amount of solid amalgam was produced in the mercury phase. From the isotopic analyses on the samples taken during the electrolyses, it was found that the isotopic equilibrium was attained between the aqueous and the liquid amalgam phases. The isotopic equilibrium constant (isotope separation factor) was determined as 1.056 (average value for all the experiments) at 20°C.     

Calculations of Thermodynamic Sulfur Isotope Effect

The isotopic reduced partition function ratios (RPFR), (s/s')f, for the ³⁴S/³²S isotopic pair were calculated for 24 sulfur compounds between 10 and 2,000K. Their magnitudes were in the following sequences; at low enough temperatures at which In(s/s')f depends only on the isotopic difference in frequency-sum, SF₆>SO₂F₂>SF₅Cl>SF₅Br>SO₄ ^2->SO₂Cl₂>SO₃>NSF₃>SF₄>SOF₂>SOCl₂>Me₂SO>SOBr₂>SO₂>SPBr₃>SCBr₂>Me₂S>SPCl₃>SCCl₂>SCF₂>SPF₃>CS₂>OCS>H₂S, and at high enough temperatures at which In(s/s')f is proportional to the isotopic difference in the sum of frequencies squared, SO₂F₂>SO₄ ^2->SO₃>SF₆>SO₂Cl₂>SF₅C1>NSF₃>SF₅Br>SOF₂>SO₂>SF₄>Me₂SO>SCCl₂>SOBr₂>H₂S>Me₂S>CS₂>SCF₂>OCS<SCCl₂>SCBr₂>SPF₃>SPCl₃>SPBr₃ where Me--CH₃. Correlation of the RPFR with molecular structure and molecular forces was discussed.

The equilibrium constants K for the ³⁴S/³²S isotope exchange reactions of all the possible pairs of 19 sulfur compounds selected out of the above 24 were calculated and their temperature dependences were investigated. Two types of temperature dependences were observed; one being smooth monotonic and the other having single cross-over with no pre-inflection.     

Assessment of the models of urania fuel oxidation in steam-rich atmosphere

The urania fuel oxidation model for a steam-rich atmosphere developed by Cox et al. using the extensive experimental database has been subsequently used widely but with some inconsistencies in implementations. They are listed and evaluated in this work to help improve the existing models as well as for future model development. The comparison of the equilibrium stoichiometry deviation, calculated using various models, is also given. Small differences between the equilibrium constants used for steam dissociation are found. In one application, the original model for steam dissociation was rewritten in terms of component partial pressures for simplification. It is shown that the modified model differs from the original model by a multiplicative factor (1 ? p _O2 /P _tot). A more complex equation that preserves total pressure is derived. However, the effect on the calculated fuel oxidation is much smaller than the effect of the uncertainty of the equilibrium stoichiometry deviation. The discrepancies in stoichiometry deviations and the estimate of the surface area of a pellet may lead to a double underprediction of fuel oxidation rate.     

CHARGE STATE DISTRIBUTIONS OF SWIFT HEAVY IONS BEHIND VARIOUS SOLID TARGETS (36 ≤Zp≤ 92, 18 MeV/u ≤E≤ 44 MeV/u)

Noting the lack of and the increasing need for information concerning heavy ion stripping in the intermediate velocity regime, we have studied a large number of ion-target systems experimentally. We present experimental charge state distributions obtained at the GANIL accelerator for several projectiles (36 ≤Z_p≤ 92) with energies ranging from 18 MeV/u to 44 MeV/u, emerging from various target foils (4 ≤Z_t≤ 79) of natural isotopic composition. The target thicknesses (from 1 μg/cm²up to several mg/cm²) are chosen to cover the pre- and post-charge-state equilibrium regimes. Charge state fractions, mean charge state, charge distribution width, and emerging ion energy are tabulated for each of the 107 projectile–target element–target thickness combinations. We also present an improvement of the semi-empirical formulae proposed by Baron et al. to predict the mean charge states and the distribution widths at equilibrium. These formulae are compared with the available experimental data.     

Measurement of the isotopic abundance of boron-10 by inductively coupled plasma-quadrupole mass spectrometry

This article describes the method for measuring the isotopic abundance of ¹⁰B in nuclear grade boron carbide using inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS). The results of investigation revealed that both the integration time and the dwell time have a major influence on the reproducibility of ICP-QMS measurements. As a result of optimization of the measurement conditions, reproducibility below 0.2% relative standard deviation (RSD) (0.17% RSD maximum) was achieved. In addition, the measured value of the isotopic abundance of ¹⁰B for each sample well agreed with the values measured by the TIMS. Thus, the method described in the present investigation was very effective in the analysis of isotopic abundance of ¹⁰B in B₄C or H₃BO₃. The results of this study suggest that ICP-QMS could be applied to the precise analysis of the isotopic abundance of ¹⁰B required in the field of nuclear applications.     

Estimate of the Efficiency of Hydrogen–Metal Hydride (Intermetallic Compound) Systems in the Separation of the Three-Isotope Mixtures H–D–T

A method is developed for calculating apparatus for separating a three-isotope mixture H–D–T by the sorption method using hydrides of metals or intermetallic compounds. Relations are established between the partition coefficients and mass-transfer characteristics, determined for binary isotopic mixtures of hydrogen, and the parameters determining the isotopic equilibrium and the kinetics of mass transfer in the system gas–solid hydride phase with three isotopes. The efficiencies of various sorbents for deprotization of deuterium–tritium mixture are compared. 4 figures, 2 tables, 7 references.     

Electromagnetic Theory of the Binding Energy of the Hydrogen Isotopes

Bieler of the Rutherford laboratory imagined in 1924 a magnetic attraction equilibrating an electrostatic repulsion between the protons. Since the discovery of the neutron and the magnetic moments of the nucleons proving that the neutron contains electric charges, nobody, as far as I know, has tried to apply electromagnetism to the nuclear interaction. As it is well known, there is an attraction between an electric charge and a neutral conductor. In the deuteron, the positive charge of the neutron is repelled and the negative charge is attracted by the proton with a net attraction. The repulsion between the magnetic moments equilibrates the electrostatically induced attraction. The calculated value is −1.6 MeV not too far from the experimental value (−2.2 MeV). The calculated 7 hydrogen isotopes stay satisfactorily along the experimental isotopic parabola. No arbitrary fitting parameter is used, only universal physical constants. The electromagnetic theory predicts a theoretical ratio between nuclear and chemical energies: \fracm_pm_e a.\frac{m_p}{m_e \alpha}.     

Disproportionation of Pu(IV): A reassessment of kinetic and equilibrium properties

Kinetic results for disproportionation of Pu(VI) and reaction of Pu(III) with Pu(VI) show that rates of in HNO₃ and HClO₄ solutions are described by trimolecular rate laws consistent with involvement of trimeric hydroxo complexes as reactive intermediates in the slow mechanistic steps. Product ratios and modeling of concentration-time curves reveal that Pu(V) is formed by reduction of Pu(VI) product in a secondary reaction. Results do not support the accepted interpretation that attributes reversible reaction and Pu(V) formation to a two-step bimolecular process. Secondary redox reactions driven by disproportionation of Pu(VI) prevent attainment of equilibrium in 1 M H⁺ and determine long-term redox chemistry. The equilibrium constant (0.00051) defined by forward and reverse rate constants for 1 M HClO₄ agrees with that (0.00049) derived from concentration data for 1 M HNO₃, but not with prior results. Disagreement of these values with that calculated from thermodynamic data suggests that steady-state Pu concentrations are controlled by kinetics. Possible pathways of secondary reactions are identified and a mechanism for reversible oxygenation of plutonium ions is described.