LiCl-KCl共晶熔盐中氧离子的去除

采用NH₄Cl和HCl气体进行LiCl-KCl共晶熔盐中氧离子的去除。在使用NH₄Cl和HCl气体去除LiCl-KCl共晶熔盐中的氧离子过程中，用钇稳定氧化锆测氧电极对熔盐中的氧离子浓度变化进行测定。结果表明，HCl与熔盐中氧离子反应生成H₂O，并将反应产物水通过HCl载带出去。NH₄Cl去除氧离子的过程也是通过NH₄Cl分解的HCl与氧离子反应除去熔盐中氧离子。NH₄Cl和HCl均能有效地去除LiCl-KCl熔盐中的氧离子，使氧离子浓度降低至10^-5～10^-4 mol/kg。     

LiCl-KCl共晶熔盐中氧离子的去除

采用NH₄Cl和HCl气体进行LiCl-KCl共晶熔盐中氧离子的去除。在使用NH₄Cl和HCl气体去除LiCl-KCl共晶熔盐中的氧离子过程中，用钇稳定氧化锆测氧电极对熔盐中的氧离子浓度变化进行测定。结果表明，HCl与熔盐中氧离子反应生成H₂O，并将反应产物水通过HCl载带出去。NH₄Cl去除氧离子的过程也是通过NH₄Cl分解的HCl与氧离子反应除去熔盐中氧离子。NH₄Cl和HCl均能有效地去除LiCl-KCl熔盐中的氧离子，使氧离子浓度降低至10^-5～10^-4 mol/kg。     

LiCl-KCl共晶熔盐的纯化

氯化锂-氯化钾共晶熔盐是电解精炼干法后处理中最常用的电解质,其含有的杂质直接影响电流效率和产物纯度。本研究分别采用高温处理、HCl气体鼓泡和恒电位电解等方法依次去除了熔盐中的易挥发物质、氧离子和金属离子等杂质,获得了较高纯度的熔盐。采用热重分析(TGA)、电化学和电感耦合等离子体原子发射光谱(ICP-AES)等方法对比了纯化前后熔盐中各杂质的含量。研究结果表明:去除易挥发杂质的最佳处理温度范围为450～650℃;去除杂质金属离子时最佳电解电位为-2.3Vvs.Ag/AgCl(摩尔分数2%),恒电位电解800s后杂质金属离子总量低于1.5×10-6 g/g(盐)。以上研究结果表明,采用高温处理、HCl气体鼓入和恒电位电解可获得纯度较高的LiCl-KCl共晶熔盐。     

LiCl-KCl体系中液态Zn阴极熔盐电解提取镨北大核心CSCD

利用液态金属作为阴极分离、提取稀土元素有很多优点。以液态金属Zn为阴极,研究Pr(Ⅲ)离子在液态Zn阴极上还原的电化学机理。在LiCl-KCl-PrCl_(3)熔盐中,分别采用循环伏安法、半积分法研究W电极和液态Zn电极上Pr(Ⅲ)的电化学还原过程。结果表明,在该实验温度下,只有一种富锌的Pr_(x)Zn_(y)金属间化合物生成。通过循环伏安法和半微分法计算了LiCl-KCl熔盐中Pr(Ⅲ)的扩散系数。根据电化学机理研究,采用液态金属Zn为阴极恒电位电解提取稀土Pr。电感耦合等离子体发射光谱仪(ICP)结果表明,随着电解时间的增长,熔盐中Pr(Ⅲ)离子的浓度逐渐降低。电解2 h后,提取效率为45.38%,当电解时间达到40 h时,提取效率为99.48%。X射线衍射(XRD)和扫描电镜-能谱(SEM-EDS)点分析结果表明,恒电位电解2 h得到的沉积物为Zn_(11)Pr_(3)。     

LiCl-KCl熔盐中Pu^(3+)在Al阴极上的电化学行为北大核心CSCD

基于固体Al阴极分离锕系元素(An)与裂变产物(FP)的电解精炼技术是极具前景的干法后处理流程之一。本研究采用暂态电化学法系统研究了Pu^(3+)在固体Al阴极上的电化学行为。循环伏安法(CV)和方波伏安法(SWV)研究结果表明,Pu^(3+)在Al阴极上可一步还原为合金,且该反应为不可逆,Pu^(3+)与Al形成合金的电位与温度的关系式为E^(θ,*)(Pu^(3+)/PuAl n)(vs.Cl-/Cl_(2))=-2.944+9.84×10^(-4)T。开路计时电位法(OCP)结合相图表明,Pu^(3+)在固体Al阴极上可生成Pu_(3)Al、PuAl、PuAl_(2)、PuAl_(3)和PuAl_(4)五种合金化合物,且计算得到了不同温度时PuAl_(4)的Gibbs生成自由能。     

LiCl-KCl熔盐中Zr(Ⅳ)于Mo电极上的电化学行为

通过循环伏安法、方波伏安法和计时电位法等研究了LiCl-KCl共晶熔盐中ZrCl_4于Mo电极上的电化学行为。探究Zr(Ⅳ)于Mo阴极的还原机理,并计算Zr(Ⅱ)的扩散系数及Zr(Ⅱ)/Zr(0)的表观标准电势。结果表明:Zr(Ⅳ)在Mo阴极还原机理为:Zr(Ⅳ)+2e=Zr(Ⅱ);Zr(Ⅱ)+2e=Zr(0)或Zr(Ⅱ)+e+Cl~-=ZrCl;ZrCl+e=Zr(0)+Cl~-;金属Zr在阳极的氧化过程为:Zr(0)-2e=Zr(Ⅱ)和Zr(Ⅱ)-2e=Zr(Ⅳ)。Zr(Ⅳ)还原为Zr(Ⅱ)和Zr(Ⅱ)还原为Zr(0)均为可逆反应,且还原过程均为扩散控制。LiCl-KCl熔盐中Zr(Ⅱ)于Mo阴极上的扩散系数与温度的关系为:ln D=-6 724/T-2.95,扩散的活化能Ea=55.9kJ/mol。Zr(Ⅱ)/Zr(0)的表观标准电位与温度的关系为:E_(Zr(Ⅱ)/Zr(0))~(Θ*)=-2.695+9.33×10~(-4) T。     

液态燃料钍基熔盐实验堆主体装置厂房总体布置研究

为实现2 MW液态燃料钍基熔盐实验堆（TMSR）主体装置厂房的合理紧凑型总体布置设计,本研究根据熔盐堆堆型特征、顶层设计和系统功能需求,确定了主体装置厂房总体设计特征,探讨了TMSR关键设备及物项的相对位置特点;同时通过合理规划厂房功能分区和设备布置,最终得到了该厂房的总体布置方案。通过本项目的实施,为实现TMSR的系统集成以及验证提供了基础平台,为小型模块化钍基熔盐示范堆的设计和建设提供技术支持及经验。     

用于熔盐体系的莫来石隔膜Ag/AgCl 参比电极的性能研究

以莫来石为隔膜材料,制备了用于高温氯化物(LiCl-KCl)熔盐体系的封闭式Ag/AgCl参比电极。采用LCR法分别测定了参比电极隔膜的电阻。同时,系统研究了参比电极的稳定性和重复使用性及平行性,重点研究了AgCl浓度对参比电极稳定性的影响。表征结果表明隔膜的组成为3Al₂O₃•2SiO₂,具有良好的离子导通性。电化学研究结果表明,AgCl摩尔分数为2.0%时,参比电极可连续稳定使用40 h以上,电位差稳定在±2 mV以内;重复使用4次后(约100 h),电位变化±5 mV;±5 mA的极化电流5 s后可于15 s内恢复初始开路电位。上述研究结果表明,莫来石隔膜Ag/AgCl具有良好的稳定性、重复使用性、可逆性,可用于熔盐电化学研究及电解工艺中电极电位的控制中。     

LiF对LiCl-KCl熔盐中电解精炼钆的影响

研究了LiF加入LiCl-KCl熔盐对钆电化学及络合行为的影响,发现LiF加入LiCl-KCl熔盐后,钆、铽的还原电位差由原来的6mV变为67mV。利用电化学方法和光谱方法研究了熔盐中钆离子和铽离子的配位结构,发现LiCl-KCl-GdCl_3(5mol%)/TbCl_3(5mol%)熔盐中存在[GdCl_6]~(3-)、[TbCl_6]~(3-)的正八面体结构;考察了LiF加入LiCl-KCl熔盐对钆、铽离子结构的影响,在LiCl-KCl-GdCl_3/TbCl_3中加入LiF后,钆离子和铽离子配位结构均为络合了3个F~-和3个Cl~-的八面体结构[GdF_3Cl_3]~(3-)和[TbF_3Cl_3]~(3-),计算得到两种八面体结构的相对累积稳定常数分别为10.98和6.38。以此为理论基础,进行了LiF对LiCl-KCl熔盐中钆电解精炼的影响研究,发现将LiF加入LiCl-KCl熔盐后进行钆电解精炼时,能以更高的去污系数分离钆。     

LiCl-KCl熔盐体系中Ce（Ⅲ）在液态Ga电极上的电化学行为

采用循环伏安法（CV）、方波伏安法（SWV）和计时电位法（CP）等暂态电化学方法研究了LiCl-KCl熔盐体系中Ce（Ⅲ）在液池Ga和液膜Ga电极上的电化学行为。以高纯Al₂O₃包覆的石墨棒作对电极，以Ag/AgCl(x=2%)为参比电极，结果表明，在液池Ga电极上，Ce（Ⅲ）可一步还原为αGa₆Ce：Ce（Ⅲ）+3e+6Ga=αGa₆Ce，该反应为不可逆过程，并受扩散控制；Ce（Ⅲ）的扩散系数与温度的关系式为：ln D=2.88-10 118.4/T；Ce（Ⅲ）/αGa₆Ce的半波电位与温度的关系式为：E=-1.701+5.472×10^-4T。此外，在Ga液膜电极上，Ce（Ⅲ）可发生欠电位沉积，形成至少三种金属间化合物。     

Recovery of Neptunium by Electrolysis of NpN in LiCl-KCl Eutectic Melts

The electrochemical behavior of neptunium nitride, NpN, in the LiCl-KCl eutectic melt containing NpCl₃ at 450, 500 and 550°C was investigated from the viewpoint of the application of electrochemical refining in a fused salt to nitride fuel cycle. The electrochemical dissolution of NpN began nearly at the potential theoretically evaluated, though this reaction was irreversible owing to small partial pressure of N₂ in the salt and the reaction rate was slow. Under the electrolysis in the NpCl₃-LiCl-KCl eutectic melt, NpN was dissolved into the salt as Np³⁺ at the anode, and Np metal was deposited at the cathode. About 0.5 g of Np metal was obtained by heating the deposit containing the salt at 800°C for 3.6 ks.     

Separation of Pure LiCl-KCl Eutectic Salt from a Mixture of LiCl-KCl Eutectic Salt and Rare-Earth Precipitates by Vacuum Distillation

In this study, the vacuum distillation of LiCl-KCl eutectic salt in a mixture of LiCl-KCl eutectic salt and rare-earth precipitates was carried out to evaluate the vaporization characteristics of LiCl-KCl eutectic salt. It was confirmed that the required time for salt vaporization was reduced by a reduction in the pressure. It appeared that the vaporization of LiCl-KCl eutectic salt containing rare-earth precipitates was decreased in comparison with that of pure salt because the salt adhered to the fine particles of the rare-earth precipitates. However, the distillation of the salt was almost achieved by elevating the surface area and further reducing the pressure. The distilled salt from the mixture consisted of 43.7 wt% LiCl and 56.3 wt% KCl. It is thought that the recovered salt can be reused because its composition is similar to the mixed ratio (44.2 wt% LiCl: 55.8 wt% KCl) of the salt used in an electrorefining process.     

Experimental Study on Fluoride Volatility Process for Thorium Fuels

Selective removal of uranium from (Th/U)O₂ by fluorination with fluorine was studied experimentally. The fluorination was performed both in a small boat and in a 2 inch inner diameter fluid-bed reactor.

Fuel particles tend to agglomerate in the reactor due to the large amount of reaction heat and the comparatively low melting point of ThF⁴. The fluorinated fuels produced in the fluid-bed reactor were found to be partially agglomerated. Fractional retention of uranium was smaller in the agglomerated parts than in the un-agglomerated, and smaller in the outer layers of the cakes than in the core.

On the other hand, it was also established beyond doubt from the results of the small boat fluorination experiment that heavy agglomeration inhibits the volatilization of uranium in the form of UF₆. Inhibition of the violet exothermic reaction by lowering the fluorine pressure in the early stage of fluorination was found to be a very effective method of obtaining high uranium recovery. It was demonstrated that more than 99% of the uranium could be volatilized within 4 to 5 hr at a temperature of 580°C.

The experimental results on the effects of temperature, particle size and fluorine concentration are presented. The variations of reaction rate observed in the course of fluorination are also discussed.     

四氟化铀和四氟化钍的高温水解

为适应钍基熔盐堆核燃料水法后处理的需求,需将乏燃料中难溶的氟化物转化为相应的氧化物形式,因此提出了高温水解的方法来实现这一目的。研究了UF4、ThF4在不同反应温度和反应时间下的高温水解行为,对其水解产物进行了结构表征和溶解实验的研究。结果表明,UF4、ThF4分别在300℃和350℃即可全部转化为相应的氧化物UO2.25和ThO2。溶解实验结果表明,二者的高温水解产物较易溶解在3mol/L HNO3和Thorex试剂中。     

Electrolysis of Burnup-Simulated Uranium Nitride Fuels in LiCl-KCl Eutectic Melts

The electrochemical behavior of burnup-simulated uranium nitride fuels containing representative solid fission product elements, UN+Mo (Mo = 2.84 wt%), UN+Pd (Pd = 4.6 wt%) and (U, Nd)N (NdN = 8.0 wt%), was investigated in the molten LiCl-KCl eutectic salt with 0.54 wt% UCl₃ in order to clarify the effects of fission products on the dissolution of actinide nitrides and the behavior of FPs in the electrorefining of spent nitride fuel. The rest potentials of burnup-simulated UN pellets were similar to that of pure UN. The electrochemical dissolution of UN began at about _0:75V vs Ag/AgCl reference electrode in all samples as well as that of pure UN. After the electrolyses at the constant anodic potential of ?0:65––0:60V vs Ag/AgCl, most of UN was dissolved into LiCl-KCl as UCl₃ at the anode, and U was recovered in the liquid Cd cathode in all samples. Furthermore, Nd was dissolved at the anode and accumulated into LiCl-KCl as NdCl₃, while Mo and Pd were not dissolved but remained at the anode.     

自动电位滴定法精密测定硝酸钍溶液中的钍

采用氧化还原电对Fe(Ⅲ)/Fe(Ⅱ)指示滴定终点,建立了钍的精密络合滴定方法。对影响测量的主要因素：自动滴定仪的滴定体积的重现性、酸度、滴定剂EDTA浓度、缓冲液加入量、Fe(Ⅲ)用量等进行了研究,确定了最佳测量条件。建立了以电位指示滴定终点的钍的精密测定方法。结果表明,钍取样量为5 mg时,相对标准偏差达到了0.1%（n=6）。     

氟碳铈-独居石混合矿中钍的分离

以氟碳铈矿-独居石混合稀土矿为研究对象,采用分步选择性碳热氯化-化学气相传输反应（SC-CVT）,实现钍与其它稀土元素的分离。当氯化反应温度为500 ℃,以活性炭为还原剂、SiCl₄为脱氟剂,在Cl₂气氛下稀土矿反应2 h时,钍的氯化产物(ThCl₄)挥发量小于1 %;继而以AlCl₃作配位体,800 ℃、Cl₂气氛下传输反应0.5 h,ThCl₄与配位体反应形成气态配合物ThAlCl₇;温度降低时,ThAlCl₇分解并沉积在600 ℃左右的温区内,AlCl₃沉积在温度低于200℃的温区内,FeCl₃主要沉积在200~350℃的温区内,从而实现放射性元素Th的分离和回收。 〖HT5”