RELAP5应用于液态燃料熔盐堆的扩展及验证

为将RELAP5程序应用于液态燃料熔盐堆的建模分析,需要对RELAP5的模型进行扩展。基于RELAP5原有的点堆模型和热工水力模型,新增了液态燃料熔盐堆点堆模型和相应的带有内热源的热工水力模型,并通过熔盐实验堆(MSRE)实验数据进行验证。结果表明,扩展后的RELAP5程序能够适用于液态燃料熔盐堆系统建模分析。     

几种典型熔盐冷却剂的热物性研究

熔盐是一种优异的传热介质。热物性数据是熔盐传热应用过程中的关键基础数据。按照制定的样品制备规范、样品测试操作流程和数据处理分析方法,采用差示扫描量热仪(Differential Scanning Calorimetry,DSC)、自主研制的阿基米德法密度仪和旋转柱体式粘度仪、改进的激光闪光法导热仪对FLi Na K、Clo Kmag和HTS熔盐的熔点、比热容、密度、导热系数、粘度系数进行了实验测量和数据评估。首次系统地提供了FLi Na K和HTS熔盐在熔点以上80 K温区的粘度系数、Clo Kmag盐的关键热物性数据。为这些熔盐的热工水力设计分析提供了准确可靠的基础数据。     

RELAP5/MOD3.3程序对非能动核电厂小破口失水事故的适用性研究

AP1000核电厂采用非能动堆芯冷却系统来缓解小破口失水事故(SBLOCA),缓解事故的理念是流动冷却。RELAP5/MOD3.3程序适用于传统核电厂SBLOCA研究,对于非能动电厂SBLOCA研究的适用性需重新研究与评估。本工作基于非能动电厂小破口失水事故的分析,结合RELAP5/MOD3.3的结构与模型,对其进行评估和改进。为验证改进后的RELAP5/MOD3.3的适用性,以AP1000小破口失水事故的验证试验台架APEX-1000为模拟对象,分析模拟DBA-02、NRC-05事故工况。分析结果表明,改进后的RELAP5/MOD3.3的计算结果与试验数据符合较好。     

RELAP5/FLUENT耦合程序的开发

热工水力数值模拟是反应堆系统设计和安全分析的重要内容,以RELAP5为代表的系统程序可对瞬态或事故工况进行快速分析,同时以FLUENT为代表的计算流体动力学(CFD)程序对堆芯局部三维现象的分析也越来越重要。为综合利用两者的优点,以RELAP5/FLUENT为基础,利用对RELAP5程序源代码的二次开发和FLUENT的用户自定义函数(UDF)进行编程,开发了RELAP5/FLUENT耦合程序。利用flibe熔盐在水平圆管流动问题验证了程序耦合的正确性;针对2 MW熔盐堆进行了稳态模拟,耦合程序能详细分析熔盐堆的热工水力行为;模拟了2 MW熔盐堆功率突变的瞬态热工水力行为,相对于单独的RELAP5,耦合程序能更好地揭示熔盐堆系统和堆芯的三维物理现象。该耦合程序可用于解决熔盐堆热工水力分析中存在的显著三维混合现象的问题。     

SCDAP/RELAP5分析UO2-Zr板型元件严重事故的方法研究

SCDAP/RELAP5是一种常见的机理性严重事故分析程序,能够分析多种类型的堆芯构件.通过对比分析SCDAP/RELAP5程序模拟棒形燃料元件与板型燃料元件堆芯在严重事故下行为的分析模型,结合UO2-Zr板型状元件堆芯的特性,提出了运用并改进SCDAP/RELAP5程序模拟UO2-Zr板型元件堆芯在严重事故下行为的研究方案.对程序结构的分析结果表明,SCDAP/RELAP5程序部分结构和模型适用于对UO2-Zr板型元件进行基本的严重事故分析,但需要通过创建新部件、研究新模型,并与已有模型的重新组合搭配才能较为精准地模拟UO2-Zr板型元件严重事故的实际行为.     

三维瞬态物理分析模型与RELAP5/mod3.2程序的耦合研究

在系统热工水力程序RELAP5/mod3.2的基础上,采用显式方法建立了堆芯三维时空中子动力学与一维热工水力计算的耦合模型,接入基于非线性迭代半解析节块法的三维瞬态物理分析模型(NLSANMT)后,形成了一个具有堆芯三维瞬态物理特性分析能力的系统计算程序NLSANMT/RELAP5(mod3.2).通过核动力反应堆温度反馈系数、堆芯功率分布参数的校算及单束控制棒失控抽出事故的模拟分析,验证了接口的正确性.验证结果表明,与RELAP5/mod3.2相比,所开发的NLSANMT/RELAP5(mod3.2)程序具有更强的堆芯物理瞬态分析能力.     

RELAP5与CFX程序耦合研究

以RELAP5与CFX程序为基础,利用并行虚拟机技术和CFX用户函数进行编程,开发了RELAP5/CFX耦合程序。在单相范围内,首先利用水平圆管喷放问题验证了程序间耦合的正确性。然后,针对双T型接管混合实验进行了模拟,相对于单独的RELAP5程序,耦合程序能更好地揭示真实的物理现象。通过后续的开发完善,耦合程序可用于反应堆安全分析中存在着显著三维混合现象的问题。     

RELAP5程序应用于二次侧非能动余热排出系统设计的初步评价

应用实验数据对RELAP5/MOD3.3程序应用于二次侧非能动余热排出系统设计进行初步评价,结果表明,系统投入初期,由于RELAP5程序的一维流动假设,针对事故冷却水池早期的内部三维对流传热模拟存在不足;系统投入后期,冷却水池内部传热为泡核沸腾,池式沸腾换热占主导地位,程序计算结果与实验结果较吻合,RELAP5/MOD3.3程序基本适用于二次侧非能动余热排出系统的稳态运行特性分析。     

低压自然循环间歇泉流动不稳定性实验研究与RELAP5程序验证

对低压条件下自然循环回路内的两相间歇泉流动不稳定性进行了实验研究。同时,对RELAP5/MOD3.2程序计算低压自然循环间歇泉流动不稳定的可行性进行了验证分析。实验结果表明,低压条件下,间歇泉流动不稳定产生的根本原因在于有效驱动压头的周期性变化,与加热段内气液两相流动的形成-消失周期密切相关。下降段内流体温度越高,波动周期越短。实验数据与RELAP5/MOD3.2程序模拟计算结果符合较好,说明RELAP5/MOD3.2程序对模拟计算低压条件下自然循环间歇泉流动不定稳性具有较好的适用性。     

基于RELAP5的氦氙流动换热计算模块开发与验证

反应堆热工系统分析程序是开展热工水力计算与安全评价的重要工具。为开发适用于氦氙气冷空间堆的热工系统分析程序,本文在RELAP5/MOD40程序中拓展了氦氙混合气体（He Xe）物性计算模块,添加了适用于He Xe的传热关系式,将拓展后程序计算值与实验值进行对比。结果表明：程序默认的Sutherlands定律用于He Xe物性计算时将引入较大误差;Dittus Bolter公式对He Xe对流换热时的Nu预测偏高,将导致不保守的壁温计算结果。拓展后的程序对He Xe压降和换热计算结果均与实验值吻合较好,验证了程序开发的正确性以及程序用于He Xe流动换热计算的功能。本研究可为系统层面程序开发奠定基础。     

Transport properties of U0.7Ce0.3O2 − x

We have determined a number of transport properties of $\text{U}{}_{0.7}\text{Ce}{}_{0.3}\text{O}{}_{\mathrm{2-x}}$ at 1273 K for various deviations from stoichiometry and compared them with available results on $\text{(UPu)O}{}_{\mathrm{2\; ?\; x}}$. They are: the electrical conductivity, Seebeck coefficient, effective charge number and chemical diffusion coefficient.A very characteristic behaviour is observed for the electronic properties of $\text{(UCe)O}{}_{\mathrm{2\; ?\; x}}$. A p-type conduction for all the studied deviations from stoichiometry (up to $\text{x = 3 × 10}{}^{\mathrm{?2}}$) is interpreted in terms of a high electronic disorder in the stoichiometric compound. Electronic disorder at stoichiometry is probably less important in $\text{(UPu)O}{}_{\mathrm{2\; ?\; x}}$, which presents a sharp p-n transition at $\text{x = 5 × 10}{}^{\mathrm{?3}}$.Ionic transport properties obtained on $\text{(UCe)O}{}_{\mathrm{2\; ?\; x}}$ indicate an approximate proportionality between the ionic conductivity resulting from oxygen ions transport and the deviation from stoichiometry. Results available on $\text{(UPu)O}{}_{\mathrm{2\; ?\; x}}$ do not appear to be compatible with ours and some arguments are presented which cast doubt on their validity.     

Equi-chemical-potential curves in ternary uranium oxides MyU1−yO2+x

Using Schuhmann's method the chemical potentials of three components in nonstoichiometric ternary uranium oxides $\text{M}{}_{\mathrm{y}}\text{U}{}_{\mathrm{1?y}}\text{O}{}_{\mathrm{2+x}}$(M = Mg and Pu) have been calculated. The obtained results are shown in the form of equi-chemical-potential curves (surface of partial molar free energy) in the composition triangle. In the hypostoichiometric region the contour lines of the surface are dense and run parallel with each other. Taking account of this fact the difficulty in attainment of homogeneity in the fabrication of mixed oxide fuel is discussed.     

Structural characterization of Nd-doped Hf-zirconolite Ca1−xNdxHfTi2−xAlxO7 ceramics

Because of its high incorporation capacity and of the high thermal neutron capture cross-section of hafnium, Hf-zirconolite (CaHfTi₂O₇) ceramic can be envisaged as a potential waste form for minor actinides (Np, Am, Cm) and plutonium immobilization. In this work, Nd-doped Hf-zirconolite Ca_1−xNd_xHfTi_2−xAl_xO₇ (x = 0; 0.01 and 0.2) ceramics have been prepared by solid state reaction. Neodymium has been used as trivalent actinide surrogate. The ceramic samples structure has been studied by X-ray diffraction and refined by the Rietveld method. This revealed that Nd³⁺ ions only enter the Ca site, whereas part of Hf⁴⁺ ions substitute titanium into Ti(1) sites and Al³⁺ ions mainly occupy the Ti(2) split sites and Ti(3) sites of the zirconolite structure. Using various spectroscopic techniques (electron spin resonance, optical absorption and fluorescence), the environment of Nd³⁺ cations in Hf-zirconolite has been studied and compared with that of Nd³⁺ cations in Zr-zirconolite (CaZrTi₂O₇). Different local environments of Nd³⁺ cations have been detected in Hf-zirconolite that can be attributed to the existence of an important disorder around Nd in the Ca site probably due to the statistical occupancy of the next nearest cationic site of neodymium (a split Ti site) by Ti⁴⁺, Al³⁺ cations and vacancies. No significant differences were observed concerning Nd³⁺ cations environment and distribution in Hf- and Zr-zirconolite ceramics.     

Phase relation and defect structures of nonstoichiometric U4O9±y and UO2+x at high temperatures

Phase relations in the composition range from $\text{UO}{}_{\mathrm{2+x}}$ to $\text{U}{}_3\text{O}{}_{\mathrm{8?z}}$ were studied by electrical-conductivity measurements and X-ray diffraction in the ranges $\text{1025°C ? T ? 1140°C}$ and . The plot of log σ versus log showed straight lines with distinct slopes, which corresponded to four regions ($\text{UO}{}_{\mathrm{2+x}}$, $\text{U}{}_4\text{O}{}_{\mathrm{9?y}}$, $\text{U}{}_4\text{O}{}_{\mathrm{9+y}}$ and $\text{U}{}_3\text{O}{}_{\mathrm{8?z}}$). The existence of the hyperstoichiometric $\text{U}{}_4\text{O}{}_{\mathrm{9+y}}$ phase was suggested in the temperature range from 1025 to 1126°C. The peritectoid temperature ($\text{U}{}_4\text{O}{}_{\mathrm{9\pm y}}\text{= UO}{}_{\mathrm{2+x}}\text{+ U}{}_3\text{O}{}_{\mathrm{8?z}}$) was estimated to be present between 1126 and 1131°C. The partial free enthalpies and entropies for the two-phase equilibrium ($\text{U}{}_4\text{O}{}_{\mathrm{9+y}}\text{+ U}{}_3\text{O}{}_{\mathrm{8?z}}$, and $\text{U}{}_4\text{O}{}_{\mathrm{9?y}}\text{+ UO}{}_{\mathrm{2+x}}$) were calculated and compared with previous results. From the dependence of the electrical conductivity on the oxygen partial pressure the nonstoichiometric defect structures of $\text{UO}{}_{\mathrm{2+x}}$ and $\text{U}{}_4\text{O}{}_{\mathrm{9\pm y}}$ were interpreted as consisting of doubly charged oxygen interstitials (O_i'') and doubly charged oxygen vacancies (V_O''). At room temperature, the homogeneity range of the U₄O₉ phase was investigated with a Debye-Scherrer camera.     

Effects of ion irradiation on the mechanical properties of SiNawOxCyHz sol-gel derived thin films

A study of the effects of ion irradiation of hybrid organic/inorganic modified silicate thin films on their mechanical properties is presented. NaOH catalyzed SiNa_wO_xC_yH_z thin films were synthesized by sol-gel processing from tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) precursors and spin-coated onto Si substrates. After drying at 300 °C, the films were irradiated with 125 keV H⁺ or 250 keV N²⁺ at fluences ranging from 1 × 10¹⁴ to 2.5 × 10¹⁶ ions/cm². Nanoindentation was used to characterize the films. Changes in hardness and reduced elastic modulus were examined as a function of ion fluence and irradiating species. The resulting increases in hardness and reduced elastic modulus are compared to similarly processed acid catalyzed silicate thin films.     

Neutron production cross sections and energies for the reactions 7Li(p,n)7Be and 7Li(p,n)7Be1

Center-of-mass best values for the normalized Legendre coefficients and the 0° differential cross sections as functions of input energy have been derived from various experimental results for the reactions ⁷Li(p,n)⁷Be and ${}^7\text{Li}\text{(p,n)}{}^7\text{Be}{}^1$ (431 keV). This information has been used to calculate laboratory differential cross sections as functions of the laboratory proton energy and neutron emission angle which are given in tabular form together with the corresponding neutron energies.     

Investigations on UAlx-Al dispersion fuels for high-flux reactors

The paper outlines the preparation of $\text{UAl}{}_{\mathrm{x}}\text{-Al}$ dispersion fuel plates for thermal high-flux reactors. The work described includes the preparation of UAl₂, UAl₃ and UAl₄ compounds by induction melting and their processing to Al-clad fuel plates using the picture-frame technique. Induction melting in alumina crucibles and subsequent homogenisation can be used to produce relatively homogeneous $\text{UAl}{}_{\mathrm{x}}$ compounds. After comminution to a predetermined size range and blending with Al, the pressed compacts can be rolled into Al-clad fuel plates. UAl₃ and UAl₂ compounds react with Al forming UAl₄. The reactions begin at about 673 K, and have an activation energy of 52.6 and 42.6 kcal/mol, respectively. The measured properties of the dispersions and UAl-phases such as thermal expansion, thermal and electrical conductivity, tensile strength, microhardness and hot hardness are affected by the concentration of the dispersed phase and can be explained in the light of existing theoretical models. Due to its potential as a high-flux reactor fuel with higher uranium content the preparation and properties of UAl₂-Al dispersions as well as the preliminary data about their stability under irradiation may be of particular interest.     

Wavelengths and classifications of emission lines due to 2s22pn−2s2pn + 1 and 2s2pn−2pn + 1 transitions, Z ≤ 28

Tables of wavelengths and classifications of observed emission lines due to 2s²2pⁿ?2s2p^{n + 1} and 2s2pⁿ?2p^{n + 1} transitions are presented. The accuracy of data derived from different experimental methods is discussed. Revised and predicted wavelengths are added. Energy levels are derived from the wavelength data.     

Damage creation in ion irradiated Si1−xGex/Si structures

Strained SiGe/Si structures have been proposed as substrates for fabrication of high speed metal oxide semiconductor transistors. However, influence of strain and/or presence of Ge atoms on damage creation during ion irradiation have not been explored to a significant extent. In this study, Rutherford backscattering spectrometry (RBS) was used to characterize Si_1−xGe_x/Si structures irradiated by 140 keV He⁺ ions at room temperature. When compared with pure Si, strained samples show enhanced damage accumulation as a function of He fluence. Channeling angular scans did not reveal any specific configuration of displacements. Possible mechanisms for enhanced damage in strained Si are discussed.     

Statistical thermodynamic study of the ternary compounds ThXyHx (X = C,N;y < 1;x < 2)

The stability and the nature of bonding in hypostoichiometric ThH₂, hcp ThC_0.46H_x and fcc ThN_yH_x (y = 0.486 and 0.692) are studied on the basis of statistical thermodynamics. The discussions are made in terms of the atomic partition function of H in these condensed phases and of the interaction energy terms. It is concluded that the nature of bonding in ThN_yH_x is approximately the same as that in ThH₂. On the other hand, the nature of bonding in ThC_yH_x is found to be significantly different from that in ThH₂.