硼氢化物(B2Hn)(n=1~6)电子特性的动力学研究

采用密度泛函(DFT)B3P86方法,结合Dunning的相关一致三重基cc-pVTZ,优化计算硼氢化物 (B₂H_n) (n=1~6)可能的几何构型,得出最稳定结构的几何参数、电子结构和振动频率等参数,给出了最稳定结构的总能量(E_T)、结合能(E_BT)、平均结合能(E_av)、电离势(E_IP)、能隙(E_g)、费米能级(E_F)和氢原子差分吸附能(E_diff)等。结果表明,硼氢化物基态稳定结构的电子态分别为：n为奇数时为双重态2A,n为偶数时为单重态1A。由于B原子属于缺电子原子,能与等电子原子H化合,通过桥键形成多中心键的氢化物,优化计算发现,硼氢化物最稳定结构都存在桥键,且n为奇数的桥键作用比相邻偶数的强。通过分析最稳定结构的电子特性发现,B₂H_n(n=1~6)中B₂H₆的电离势和能隙最大,桥键比端键长,红外光谱强度最大,说明该硼氢化物最稳定,且其氢原子差分吸附能最大,储氢性能相对最好。     

锑烯表面铀、钍、钚的吸附性能研究：线性响应方法结合密度泛函理论

基于密度泛函理论（Density Functional Theory,DFT）研究了锕系元素铀（U）、钍（Th）、钚（Pu）在二维金属材料锑烯表面的吸附特性。采用线性响应法拟合得到描述铀、钚5f轨道电子强格点库仑作用的哈伯德U值分别为2.24 eV和2.84 eV。利用DFT+U计算发现，锑烯难以吸附钚原子（吸附能为负值），而对铀、钍原子具有较强的表面化学吸附以及丰富的稳定吸附位点。铀和钍原子能量上最稳定的吸附位点分别为桥位——孔位之间和孔位，吸附能分别为4.40 eV和3.62 eV。通过电子结构、电荷转移和最高占据态轨道波函数分析发现，铀、钍原子使锑烯的带隙中出现杂质态，并与锑烯之间通过强p-d轨道耦合使其稳定吸附。进一步计算了吸附率随温度的变化，得出铀和钍在锑烯表面的解吸温度分别达到837 K和660 K。结果预示锑烯是一种良好的铀、钍吸附材料，在海水提铀等领域具有潜在应用。     

铀与O_2相互作用的从头计算研究

用量子化学从头计算(ab initio)方法,计算了U—O体系气态分子的优化几何构型、总能量、振动频率和成键情况,并构筑了该体系有关相互作用的势能面。计算的铀氧化物优化构型和振动频率同现有的实验数据符合较好。布居数分析结果表明在形成铀氧化物时,主要是U5f电子参加了与氧成键,但在UO和UO_3中,U6d轨道电子成键的成分相对于UO_2有所增大。同时,由于铀的7s和6d及5f轨道能量很接近,形成ds杂化轨道并参与成键。各氧化物的第一电离能同文献数据符合较好。势能面分析结果表明铀氧化产物取决于铀原子与O_2相互作用的方式。     

铀与O_2相互作用的从头计算研究

用量子化学从头计算(ab initio)方法, 计算了 U—O 体系气态分子的优化几何构型、总能量、振动频率和成键情况,并构筑了该体系有关相互作用的势能面。计算的铀氧化物优化构型和振动频率同现有的实验数据符合较好。布居数分析结果表明在形成铀氧化物时,主要是 U5f电子参加了与氧成键,但在 UO 和 UO3中,U6d 轨道电子成键的成分相对于 UO2有所增大。同时,由于铀的 7s 和 6d及 5f 轨道能量很接近,形成 ds 杂化轨道并参与成键。各氧化物的第一电离能同文献数据符合较好。势能面分析结果表明铀氧化产物取决于铀原子与 O2相互作用的方式。     

热压烧结UN陶瓷芯块的性能

UN燃料具有铀密度高、熔点高、热导率高、热膨胀系数低、辐照稳定性好等优点,是未来空间核电源、核火箭、快堆和ADS的重要候选燃料。本文采用金属铀粉与氮气在300～400℃直接发生化合反应,制得单相U₂N₃粉末。粒度为38.3 μm的U₂N₃粉末在1 600 ℃真空热压烧结,制得相对密度为93.5%、存在少量金属铀相的UN陶瓷;而18.1 μm的U₂N₃粉末在1 550 ℃真空热压烧结,制得相对密度为96.1%、不残留金属铀相的UN陶瓷,U与N的总质量分数为99.57%,每个金属杂质含量均低于50 μg/g,氧含量为1 048 μg/g,碳含量为502 μg/g。U₂N₃在1 027 ℃以上将会完全分解成UN,UN在1 627 ℃以上也会发生分解。     

Be_n(n=1～6)团簇吸附H_2的密度泛函研究

采用密度泛函广义梯度近似(GGA)的PW91方法,用全电子基组DNP对Ben(n=2～6)团簇几何结构进行优化,计算了团簇的总能、平均结合能、振动频率、最高已占据轨道能级、最低未占据轨道能级、能隙、垂直电离势和垂直亲和势。在Ben(n=1～6)团簇的顶位、桥位和穴位吸附H2后,进行了吸附物的几何优化和能量计算,得到最佳吸附位,并计算了吸附前后的总态密度和Mulliken电荷布居。结果表明:团簇中Be原子数增多,稳定性增强;吸附H2的吸附能处于0.0061982～0.0089722a.u.之间;随着Be团簇原子数量增加,与H的s-p杂化程度增强;吸附位对应的电荷转移量越大,吸附越牢固。     

O2在UC(001)表面吸附的第一性原理研究

本文使用GGA+U方法研究了O₂在UC(001)表面的吸附、解离过程。结果表明：U_eff=1.5 eV能很好地再现晶格常数a和内聚能E_coh的实验结果；经过离子弛豫，最表面的两个原子层出现分层现象，各自形成两个亚层；O₂分子的吸附构型对吸附过程影响较大，吸附能在2.21～8.55 eV之间变化。通过Bader电荷、差分电荷和态密度分析，可确定O₂分子的解离活化机理为U的5f/6d电子转移至O₂的π2p和π*2p轨道。     

Thorex流程钍铀分离工艺单元计算机模拟研究

在Th(NO₃)₄-UO₂(NO₃)₂-HNO₃-H₂O/30%TBP-正十二烷分配比模型的基础上,使用串级萃取理论编写了Thorex流程钍铀分离工艺单元(1B)的计算机模拟程序,该程序可对钍、铀、硝酸的萃取行为进行模拟计算。通过文献数据对该程序的可靠性进行了验证,结果表明,该程序的计算值与文献值符合良好。在此基础上利用该模拟程序对钍铀分离单元的工艺参数进行了计算分析,结果表明：工艺运行状况受工艺参数的综合影响,其中反萃液(1BX)硝酸浓度是影响因素之一,铀产品(1BU)中钍含量随酸度的增大而增大,而钍产品(1BT)中铀含量则随酸度的增大而降低,酸度过大或过小均不能实现二者的良好分离;1BX流比对分离效果的影响与酸度相反,随着1BX流比的增大,1BU中钍含量显著降低,而1BT中铀含量增大;补萃剂(1BS)流比对分离效果的影响与1BX流比的影响趋势相反,因此在工艺寻优中可利用本程序选择分离效果最好的条件组合。此外,还可利用本程序进行其他工艺要求的钍铀分离工艺参数寻优计算等。     

铀与CO相互作用的理论研究

从理论上研究铀氧(碳)化产物的电子结构和氧化过程中电子的转移过程,从微观上揭示铀表面氧化反应初始阶段的机理,对探讨金属铀表面防腐的方法有重要意义。用量子化学从头计算(ab initio)方法, 计算了铀、氧和碳三元体系气态原子和分子的优化构型、总能量、振动频率和成键情况。并在单点能计算的基础上构筑了铀与 CO 相互作用的势能面。计算的铀氧化物和碳化物优化构型和振动频率同现有的实验数据符合较好。U5f 在铀与氧或碳的键合中起着重要作用。计算结果说明 CO 在铀上的吸附属于解离吸附,而且,铀更倾向于从碳端与 CO 相互作用,势能面分析结果也说明了这点。同时,也证明了铀与 CO 相互作用的初始产物有 UCO,UC和 CUO等。     

铀与CO相互作用的理论研究

从理论上研究铀氧(碳)化产物的电子结构和氧化过程中电子的转移过程,从微观上揭示铀表面氧化反应初始阶段的机理,对探讨金属铀表面防腐的方法有重要意义。用量子化学从头计算(ab initio)方法,计算了铀、氧和碳三元体系气态原子和分子的优化构型、总能量、振动频率和成键情况。并在单点能计算的基础上构筑了铀与CO相互作用的势能面。计算的铀氧化物和碳化物优化构型和振动频率同现有的实验数据符合较好。U5f在铀与氧或碳的键合中起着重要作用。计算结果说明CO在铀上的吸附属于解离吸附,而且,铀更倾向于从碳端与CO相互作用,势能面分析结果也说明了这点。同时,也证明了铀与CO相互作用的初始产物有UCO,UC和CUO等。     

Etude des nitrures d'uranium, de plutonium et de leurs solutions solides

The development of uranium and plutonium nitrides or their solid solutions as a possible fuel element for fast breeder-reactors, is conditioned by possibilities of production of those compounds on a large scale and by the evaluation of their general properties.

A low temperature preparation method of uranium nitrides is described. Under pressure nitrogen reacts with massive-metallic uranium samples when superficially hydrided. Higher nitrides so produced have a mean composition range UN_1.75-UN_1.77. Uranium mononitrides UN is obtained by dissociation of UN_1.77 under vacuum at 800° C or higher temperatures.

With plutonium for which no higher nitride exists, mononitride is directly prepared by metal nitration.

Under the same conditions no solid solutions (UPu)N can be prepared by nitration of U/Pu alloys; a mixture of (UN)1.77 and (UPu)N is obtained.

Densities of 87 % of theorical density are obtained by natural sintering of UN compacts. Sintering improvement and grain growth are observed when an uranium liquid phase is present.

Low metallic additions do not improve the sintering behaviour, but bodies with 90 % of theoretical density can be obtained with small addition of oxydes such as UO₂, ZrO₂.

After diffusion in solid state of UN—PuN mixture, the solid solution obtained can be sintered to 90 % of theoretical density.

The dissociation of UN and PuN above 1650° C and the strong volatilization of PuN at high temperature are characteristic features of those compounds.

The lattice parameter of (UPu)N solid solutions prepared at temperature 900° C increases linearly with PuN content. For solid solutions annealed at higher temperature the lattice parameter follows a linear variation with a different slope.

In conclusion general properties of nitrides and carbides as a possible fuel elements are compared.     

First principles modelling of oxygen impurities in UN nuclear fuels

We report results of first principles VASP supercell calculations of O impurity in UN fuels placed either at an interstitial tetrahedral position or as a substitution for a host N ion. In the latter case O perfectly fits into N site producing no lattice distortion. Such the O substitutional impurity only slightly affects the formation energies of U and N vacancies nearby. In both interstitial and substitutional positions O atom attracts the additional electron density and transforms into the negatively charged ion. Oxygen incorporation into pre-existing N vacancy is energetically more favourable than into the interstitial position. The O impurities produce an additional peak at the low energy side of N contribution to the DOS calculated for uranium mononitride which could be used for the O identification by means of the UPS spectroscopy. We compare also the DOS calculated for UN and hypothetical isostructural UO. Both O solution and incorporation energies are negative, indicating that O penetration into UN fuel is the energetically favourable. The migration energy of the interstitial O ion is estimated as 2.8 eV.     

相干谐波辐射实验的测量和控制系统

电子束和种子激光一同通过光学速调管时,产生相干谐波辐射,这是获得短长波相干光的一种很有希望的途径。为产生相干辐射,光学速调管波荡器磁极间隙,种子激光波长和电子能量三者必须满足共振条件,电子束团和种子激光脉冲在时间上必须严格同步。为使某次相干谐波辐射达到极大值,光学速调色散段磁极间隙必须调节,介绍了相干谐波辐射的测量、种子激光与电子束的同步和光学速调管极间隙调节系统。     

High Energy Electron Accelerators

The Cambridge Electron Accelerator is now in full-scale operation for research at energies up to 6 Bev, five times higher than earlier electron accelerators. The machine, a synchrotron, uses a ring of 48 alternating gradient magnets in a circle 236 feet in diameter. Electrons are accelerated by RF fields produced in a set of sixteen resonant cavities spaced around the orbit. The frequency used is 476 Mc/s, the 360th harmonic of the orbital frequency. Injection of 30-Mev electrons is accomplished by using a linear accelerator operating at 2855 Mc/s. The main machine accepts and-accelerates to maximum energy beam currents of up to 1.2 x 1012 electrons/sec. The quality of the beam is fully as good as that from a linear accelerator. The CEA laboratory operates five days a week on a three-shift basis and has a staff of 160 people.     

Optical properties of uranium mononitride from 0 TO 74 eV

Optical constants have been obtained for polycrystalline UN from 0 to 74 eV. The lower energy data have been compared with band structure theory and higher energy data with X-ray emission data. The P_IIIn level of U in UN has been set at − 24 eV and the P_II level at −32 eV relative to the Fermi Energy by analysis of these data. The calculated energy loss functions —Im(ε+1)⁻¹ and — Im(1/ε) are interpreted in terms of a combination of single electron transitions and collective oscillations.     

HPuO分子激发态的外场效应

采用密度泛函(DFT)方法B3LYP/Gen,在Pu为相对论有效原子实势(RECP)基组水平上,优化计算得到了分子轴方向不同电偶极场（－0.005～0.005a.u.）作用下的HPuO的基态几何结构、偶极矩和分子总能量。在优化构型下,用同样的基组,采用含时密度泛函(TDDFT)方法(TD-B3LYP),研究了同样外电场条件下对HPuO的激发能的影响。计算结果表明,在外场作用下,对HPuO的前5个激发态电子跃迁光谱属于红外 远红外光谱,波长为1046.0～3038.7nm,这是钚原子的奇异特征。激发能与外电场的关系近似满足Grozema等提出的关系。     

Preparation of Uranium Nitrides from Uranium Tetrachloride

A study was made of UN preparation by two-step reactions with UCl₄, Al and N₂ gas. In the first step, an intermediate uranium nitride with an N/U ratio of 1.68 resulted from the reaction of UCl₄ with A1 under constant flow of N₂ at reaction temperatures higher than 800°C. The X-ray pattern of the intermediate nitride did not correspond to any previously known uranium nitride. A maximum conversion efficiency of about 70% was obtained at temperatures between 800° and 1,000°G for the first reaction. In the second reaction, the intermediate nitride was heat treated under vacuum. To obtain single phase UN from the intermediate nitride, the heat treatment required a temperature of at least 1,100°C, at which the minimum holding time was 60 min.     

Compressive creep of sintered UC-UN solid solutions

Compressive creep of slightly hypo-stoichiometric uranium carbonitrides sintered from UC and UN powder mixture was studied at temperatures of 1310 and 1500° C. The creep rate as a function of C/N mole fraction showed a maximum near the composition $\text{N/(C+N) =}\text{1}\text{4}$(in moles) and a minimum near $\text{N/(C+N) =}\text{3}\text{4}$. This behaviour was correlated with the recent experimental evidence of the anomalies in the elastic constant and melting point, and thermodynamic discussions on the deviation of uranium carbonitrides from the ideal solution of UC and UN.     

重屏蔽条件下铀材料丰度的时间关联测量分析

针对高原子序数物质屏蔽下的铀材料，提出了一种新的技术方法来估算其铀丰度。首先，用D-T中子发生器的14 MeV中子对铀材料及屏蔽层进行主动质询，同时利用裂变射线探测器得到裂变中子/γ射线时间关联测量谱。然后，利用成像探测器建立的断层扫描图像得到铀材料及屏蔽层的几何和材料参数，并调用不同的铀丰度参数进行蒙特卡罗模拟计算，得到时间关联计算谱。最后，寻找与测量谱最匹配的模拟谱，确定铀材料的实际铀丰度。通过对比裂变射线探测器实验测量得到的所有裂变中子/γ射线时间关联谱，结果发现在各种屏蔽层状态下，高浓铀材料与贫化铀材料的时间关联谱均存在显著差异，可用时间关联谱作为区分不同铀材料丰度的重要技术特征；对于相同铀丰度和屏蔽状态下的铀材料，模拟谱与测量谱吻合较好，表明时间关联谱的模拟与实验分析可为铀材料铀丰度的估算提供技术基础。