Molecular Dynamics Simulations of Thermal Properties of Solid Uranium Dioxide

Molecular dynamics simulations are performed with the recently developed empirical interaction potential by Morelon et al. Thermodynamics properties of solid UO2 that have been assessed include melt point, density, enthalpy, heat capacity, lattice parameter variation with temperature, mean-square-displacement and diffusion coefficients of oxygen ion. The results are compared with the data in literature and it is suggested that the rigid ionic potential provides perfect results below the superionic range. The data showing thermodynamics properties will become unacceptable when the temperature is higher than 2500 K. Compared with the previous empirical potentials, the empirical potential developed by Morelon et al. improves the agreement of these data with the recommend ones.     

UO2分子的多体项展式势能函数

采用Ｇａｕｓｓｉａｎ９４ Ｗ 程序和相对论有效原子实理论模型优化出ＵＯ２ 分子稳定构型为线性Ｏ—Ｕ—Ｏ（ Ｄ∞ｈ） ,亚稳定构型为Ｕ—Ｏ—Ｏ（ Ｃ∞ｖ） ,计算出平衡核间距和振动频率．然后根据微观可逆性原则,准确地判断了ＵＯ２ 分子的离解极限．运用多体项展式理论方法,导出了基态ＵＯ２ 分子的分析势能函数,绘出其势能面等值图,准确地展现了Ｏ—Ｕ—Ｏ（ Ｄ∞ｈ） 稳定结构和Ｕ—Ｏ—Ｏ（ Ｃ∞ｖ） 亚稳定结构,根据势能面等值图讨论了Ｏ（３Ｐｇ） ＋ ＵＯ 反应和Ｕ＋ Ｏ２（ Ｘ３Σ－ｇ ） 反应的势能面静态特征     

火焰原子吸收光谱法测定含钆二氧化铀芯块中微量铯

本文报道了用火焰原子吸收光谱法测定含钆二氧化铀芯块中微量铯的方法。试样经硝酸、氢氟酸分解，其体铀用聚偏氟乙烯－磷酸三丁酯（（TBP）色层术上萃取而分离除去，在氯化钾存在下的1.6mol/L硝酸介质和60％甲基异丙基丁酮－甲醇混合溶剂中，在空气－乙炔火焰下测其铯的原子吸收强度，而得出铯的含量。方法简便、快速、灵敏。测定范围0.2-1.6μg/mL，回收率为96％－102％，精密度优于±10％。     

U^＋＋的能级与UO^＋＋2的电子状态

用全相对论量子力学方法计算了电子组态为［Ｒｎ］５ｆ２６ｄ１７ｓ１的Ｕ的全部２１４个电子状态的能级，基态为５Ｋ５。设ＵＯ２为线型（Ｒ∞ｈ），Ｕ和Ｏ２均为基态，则ＵＯ２的可能电子状态有３，５，７Σ－ｇ，３，５，７πｇ，…。ＵＯ２的基态不大可能为１Σ＋ｇ。     

ICP—AES法测定陶瓷二氧化铀芯块粉末标准物质中铝,钡,钴,钽,钛和钒

随着大型核电事业的发展,对核纯陶瓷二氧化铀芯块的质量控制、质量保证及对测试方法的校准和确认等方面,迫切需要研制核纯陶瓷二氧化铀芯块的杂质标准物质.测定铀及其化合物中痕量杂质元素,需预先将铀与杂质元素分离,国外大多采用萃取法,国内都采用萃取色谱法.所用萃取剂有TBP、TOPO以及TEHP等.本文用我院合成的237季铵萃取树脂进行分离富集,并用ICP-AES法同时测定陶瓷二氧化铀芯块粉末标准物质中铝、钡、钴、钽、钛和钒.     

锆掺杂二氧化铀中氧缺陷扩散机制的密度泛函计算研究

应用基于量子力学的密度泛函计算和过渡态搜寻的CI-NEB方法,研究了锆掺杂前后二氧化铀晶格中氧空位和氧间隙本征缺陷的扩散机理,计算了扩散路径和扩散能垒。计算结果表明,锆掺杂使得氧空位缺陷<100>方向的扩散能垒降低了0.40 eV,氧间隙交换机制的扩散能垒降低了0.07 eV。锆掺杂后,氧空位远低于氧间隙缺陷的扩散能垒。最后分析了扩散过程中氧原子和金属原子之间的键长,说明锆掺杂导致点缺陷扩散能垒降低与晶格畸变密切相关。Oxygen vacancy and interstitial diffusion mechanisms in uranium dioxide doped with zirconium are investigated by the density functional theory calculations. The migration pathways and barriers are identified using the climbing-image nudge elastic band (CI-NEB) method. It is found that the vacancy migration barrier along the <100> direction decreases by about 0.40 eV, while the indirect interstitial migration barrier decreases by about 0.07 eV in the zirconium doped uranium dioxide. The oxygen vacancy migration barrier is far lower than the oxygen interstitial migration barrier in the uranium dioxide doped with zirconium. Based on the analysis of bond length of local structures during the migration of oxygen atoms, it is concluded that the lattice distortion may be responsible for the reduction of oxygen migration barrier.     

库仑法测定二氧化铀粉末中水分含量

随着科学研究的发展和生产技术的进步,水分的定量分析已被列为各类物质理化分析的基本项目之一,成为各类物质的一项重要的质量指标。对于物料中水分含量的测定,现阶段的测试手段可分为两类:一是使用绝对法测定,可直接获得含水量(例如通过干燥计算失重)。这些方法包括常压干燥法、红外干燥、微波干燥和真空器干燥法等[1-7]。以上4种方法都属于热重法。二是采用推理法,间接测定水分含量。可推测样品中与物理特性相关的水分     

ICP-AES法测定二氧化铀中16种杂质元素

前言国内外有关UO_2中金属杂质的分析方法,除用化学法及原子吸收法单独测定一些单个杂质元素外,主要是采用一般电弧或火花光源激发的载体分馏发射光谱法,或化学光谱法。近年来随着ICP光源的发展,国内外已逐步开展了用ICP—AES法测定铀化合物中杂质元素的研究。从分离方法看,国外多采用萃取法,而国内近年来多采用萃取色层法,只是所用的     

Improvement of a Fission-Like Model for Nuclear α Decay

Theα decay constant is the product of the penetrability P and assault frequency vo in the fission-like model. An effective assault frequency Pv replacing the previous assault frequency uo is introduced for improvement of a fission-like model named the generalized liquid drop model （GLDM） to describe the nuclear α decay process more accurately. Two analytical formulae are proposed for the effective assault frequency due to experimental data within the GLDM. The improved model can be used to give accurate calculations for α decay half-lives.