隔膜电解还原法制备四价铀的研究

研究了在ＵＯ２（ＮＯ３）２－ＨＮＯ３－Ｎ２Ｈ５ＮＯ３体系中，采用阳离子交换膜作隔膜，钛板为阴极、镀铂钛网为阳极的电解还原制备价铀的方法，探讨了阴极电位，电流密度，硝酸浓度、肼浓度、Ｕ浓度、温度等对Ｕ（Ⅵ）的电解还原的影响，在最佳工艺条件下，可定量将Ｕ（Ⅵ）还原，制备得到四价铀浓度大于１５０ｇ／Ｌ的溶液。     

动态膜电解制备四价铀中电流效率的讨论

进行了不同电流密度（40～160 mA/cm²）下电解制备四价铀的研究。研究结果表明,采用动态膜电解制备四价铀,能在保证六价铀转化率的前提下维持较高的电流效率,最终保证了四价铀制备过程的高效率。但在电解过程后期（大部分六价铀已转化为四价铀）,若采用高电流密度,电流效率迅速下降,而采用低电流密度时仍能维持较高的电流效率。为进一步提高四价铀制备过程的电流效率,研究了程序控制电流密度阶梯减小的电解方式对电解过程后期的电流效率的影响。研究结果表明,与恒定电流密度电解方式相比,采用阶梯形减小电流密度的电解方式,可有效地提高电解过程的电流效率,有助于减少副反应的发生。     

电解还原制备U（IV）过程中的阳极材料腐蚀研究

用间歇电解还原法研究了在有机玻璃电解槽中阳极镀铂钛网在ＵＯ２（ＮＯ３）２－ＨＮＯ３－Ｎ２Ｈ５ＮＯ３－Ｈ２Ｏ体系中的耐腐蚀情况。研究结果表明：在无隔膜电解还原时，镀铂钛网上的Ｐｔ的腐蚀速率极低（〈２．５×１０＾－２μｍ／ａ），而在以阳离子交换膜作隔膜的电解还原中，镀铂钛网上的Ｐｔ有明显的腐蚀，其腐蚀速率为５．７μｍ／ａ。对这两种情况下Ｐｔ的腐蚀速率明显差别的原因进行了分析讨论。     

氯化锂熔盐中八氧化三铀电解还原基础研究

将氧化物乏燃料直接电解还原为粗金属的过程是目前以电解还原-电解精炼为特征的主流干法后处理流程的重要步骤。二氧化铀（UO₂）是乏燃料的最主要成分,将致密的UO₂芯块转化为八氧化三铀（U₃O₈）粉末后,再进行电化学还原能有效提高还原速率。因此,以U₃O₈为研究对象,开展其在氯化锂（LiCl）熔盐中的电解还原机理研究,对后处理干法流程的开发具有重要的现实意义。本文在650 ℃的LiCl熔盐中,采用循环伏安法和恒电位电解法,研究U₃O₈的电解还原行为;对电解后的样品,运用XRD、SEM等手段分析其组成和形貌,并推测相应的还原机理。     

单甲基肼还原Np（Ⅵ）：Ⅰ.反应动力学研究

用分光光度法研究了ｃ（ＣＨ３Ｎ２Ｈ３）、ｃ（ＨＮＯ３）、ｃ（ＵＯ２＋２）、ｃ（ＨＮＯ２）、离子强度和温度等因素对Ｎｐ（Ⅵ）还原速率的影响。求出了Ｎｐ（Ⅵ）还原反应级数和不同反应条件下的表观反应速率常数，建立了反应速率方程式。温度为２４℃时，还原反应的表观反应速率常数ｋ２＝６１．３ｍｉｎ－１。反应的活化能为（５９．６２±１．１２）ｋＪ·ｍｏｌ－１。提高单甲基肼浓度，降低ＨＮＯ３浓度和升高温度有利于加快Ｎｐ（Ⅵ）的还原；离子强度和ＵＯ２＋２浓度对反应速率无明显影响；当反应体系中有ＨＮＯ２存在时，Ｎｐ（Ⅵ）还原速率明显提高。     

硝酸铀酰在电还原脉冲筛板柱中的电解还原

在直径5cm的电解还原脉冲筛板柱中,用30%TBP(煤油)-UO_2(NO_3)_2-HNO_3/N_2H_5NO_3-HNO_3(H_2O)体系,研究了诸因素下U(Ⅵ)电解还原性能。结果表明:在Purex过程1BX柱工艺条件下,阴极电位、有机相U(Ⅵ)浓度、温度、阴/阳极面积比及柱子的特征几何系数等对U(Ⅵ)电解还原有显著的影响。柱内有合适的铀、硝酸及肼的浓度剖面。电解过程中产生的气体对工艺过程无干扰,生成的氢气及叠氮酸远低于规定的安全浓度限。通过调整某些工艺参数,可以有效地控制U(Ⅵ)浓度,以满足铀/钚分离的要求。     

电解还原制备U(Ⅳ)过程中的阳极材料腐蚀研究

用间歇电解还原法研究了在有机玻璃电解槽中阳极镀铂钛网在ＵＯ２（ＮＯ３）２－ＨＮＯ３－Ｎ２Ｈ５ＮＯ３－Ｈ２Ｏ体系中的耐腐蚀情况。研究结果表明：在无隔膜电解还原时，镀铂钛网上的Ｐｔ的腐蚀速率极低（＜２．５×１０－２μｍ／ａ），而在以阳离子交换膜作隔膜的电解还原中，镀铂钛网上的Ｐｔ有明显的腐蚀，其腐蚀速率为５．７μｍ／ａ。对这两种情况下Ｐｔ的腐蚀速率明显差别的原因进行了分析讨论。     

Corrosion behavior of ceramic structural materials in an electrolytic reduction process

The electrolytic reduction of spent oxide fuel involves the liberation of oxygen in a molten LiCl electrolyte, which results in a chemically aggressive environment that is too corrosive for typical alloying structural materials. Therefore, the choice of the optimum material for the processing equipment that handles molten salt is critical. We investigated the corrosion behaviors of CaO-stabilized ZrO₂ (CSZ) and mullite (Al₆Si₂O₁₃) at 650°C for 168 h in molten (1, 3) wt% Li₂O–LiCl. The as-received and tested specimens were examined by scanning electron microscopy/X-ray energy dispersive spectrometry and X-ray diffraction. CSZ showed a much better hot-corrosion resistance in the presence of Li₂O–LiCl molten salt than mullite. The surface corrosion layers of mullite consisted of LiAlSiO₄ in 1 wt% Li₂O–LiCl, and a LiAlO₂ phase appeared as the Li₂O concentration increased to 3 wt%. Furthermore, Li₂SiO₃ was the only corrosion product observed at 3 wt% Li₂O–LiCl. The surface corrosion layers of CSZ were composed mainly of tetragonal-ZrO₂ with partial monoclinic-ZrO₂ in 1 wt% Li₂O–LiCl, and a Li₂ZrO₃ phase appeared at 3 wt% Li₂O–LiCl. There was no corrosion product detached from the surface for those specimens. CSZ was beneficial for increasing the hot-corrosion resistance of the structural materials that handle high-temperature molten salts containing Li₂O.     

同位素金属氧化物的还原技术研究

系统研究了同位素金属氧化物的3种常用还原技术,即高温还原、氢气还原和电解还原,并利用这3种还原技术成功将大量金属同位素氧化物还原成相应的金属同位素单质,它们的平均还原收集效率分别为93.1%、98.9%和94.2%。最后,在扫描电子显微镜上分析了所还原金属的纯度,结果显示,氢气还原的金属纯度最好,均在99%以上;其次是高温还原的金属纯度,在98%以上;电解还原的金属中杂质含量相对最高,其纯度在92%～97%之间不等。     

Formation mechanism of Al_2O_3/MoS_2 nanocomposite coating by plasma electrolytic oxidation(PEO)

In this study, an Al_2O_3/MoS_2 nanocomposite coating was created on an aluminum 1050 substrate using the plasma electrolytic oxidation method. The zeta potential measurements showed that small MoS_2 particles have negative potential and move toward the anode electrode.The nanoparticles of MoS_2 were found to have a zeta potential of-25 mV, which prevents suspension in the solution. Thus, to produce an Al_2O_3/MoS_2 nanocomposite, one has to use the microparticles of MoS_2. The X-ray diffraction analyses showed that the produced coatings contained α-Al_2O_3, γ-Al_2O_3, and MoS_2, and that the size of MoS_2 particles can be reduced to 30 nm. It was observed that prolonged suspension in the electrolyte results in an enhanced formation of an Al_2O_3/MoS_2 nanocomposite. Using the results, it was hypothesized that the mechanism of the formation of the Al_2O_3/MoS_2 nanocomposite coating on the aluminum 1050 substrate is based on electrical energy discharge.     

在UO_2(NO_3)_2-TBP-CCI_4有机相中光化还原制备铀(Ⅳ)的研究

本文的目的是研究在TBP有机相中光化还原铀(Ⅵ)以制备铀(Ⅳ)。选用了高压汞灯作为激发光源,CCl_4为TBP的稀释剂。研究了反应温度、原始水相溶液组成等因素对铀(Ⅳ)产额和亚硝酸生成量的影响。推荐了制备铀(Ⅳ)的适宜条件。     

Nuclear and thermal effects during electrolytic reduction of deuterium at palladium cathode

In a galvanostatic experiment of charging deuterium in a palladium cathode, nuclear and thermal effects were found. A sintered palladium electrode shaped as parallelepiped was used. After 6 days of electolysis at 200 mA/cm², a simultaneous emission of neutrons, tritium excess in the electrolytic solution, and temperature rapid increase was observed. During the event which lasted 4 minutes, we counted 7.2×10⁵ neutrons while the electrode temperature reached 150°C. Electrochemical procedure for charging the palladium electrode by deuterium using galvanostatic pulses as well as the associated electrode temperature trends are shown.     

用TBP溶剂萃取法制备核电纯二氧化铀

研究了以粗制铀化学浓缩物为原料、采用TBP溶剂萃取法制备核电纯UO2的工艺.铀浓缩物经过预处理,有效地降低了水分含量,去除了有机杂质,改变了易于生成胶体的杂质形态,消除了其对后续工序的影响,然后以φ＝30％TBP-煤油溶液作萃取剂,从300～400 g/L高浓度铀溶液中萃取铀,负载有机相以酸、水两段联合洗涤去除杂质,用...     

Thermogravimetric study of the kinetics of lithium titanate reduction by hydrogen

The lithium titanate powder was synthesized by gel-combustion route. The mechanism and the kinetics of hydrogen interaction with lithium titanate powder were studied using non-isothermal thermogravimetric technique. Lithium titanate underwent reduction in hydrogen atmosphere which led to the formation of oxygen deficient non-stoichiometric compound in lithium titanate. One-dimensional diffusion appeared to be the most probable reaction mechanism. The activation energy for reduction of lithium titanate under hydrogen atmosphere was found to be 27.4 kJ/mol/K. Structural changes after hydrogen reduction in lithium titanate were observed in X-ray diffraction analysis.