液态锂铅合金中微量氚的回收

解决全球能源问题的聚变反应堆一直备受关注,其中由欧盟、俄罗斯、中、韩、印、日等多方合作的ITER(International Thermonuclear Experimental Reactor)计划便是一个代表性的进展标志.ITER实验包层工作组将液态锂铅实验包层模块列为重点开发对象,中国提出的双功能锂铅实验包层模块DFLL-TBM(Dual FunctionLithium Lead-Test Blanket Module)是主要研究方案之一,液态锂铅集氚增殖剂、冷却剂和中子倍增剂于一身,可采用鼓泡器方式实现氚的提取.有关含氚固体废物的回收早有报道,但主要集中于贮氢材料中氚的同位素交换和氘氚化锂残渣中的氚回收,而高温液态合金中氚的回收还未见报道.如果要将液相锂铅中的氚滞留量降低到包层设计的要求,则必须使其上方的氚分压不超过107Pa,采用单纯的氦吹洗或真空脱气难以满足要求,102Pa是它们所能达到的最低极限压力,这是因为在低氚浓度下,由液相转入气相的氚速率是受氚在液相、气相及气-液界面的扩散过程所限制.为了提高从锂铅合金中回收氚的效率,减小氚在液相和气相的分子扩散阻力及气体在液相的滞留时间,本文采用氦吹洗气以及其与氢、氘的混合气作为交换载带气,利用同位素效应(isotopic effect),对液态锂铅合金中的微量氚开展实验回收的预先研究,期望对今后包层氚提取系统(TES)的工程化设计与建造提供技术支持.研究结果显示:随着交换温度的升高,氚的回收率明显增加,并且温度越高,第一次解吸的氚量越大.623K时,同位素交换效果较差,氚回收率较低;723K时经过6次交换后氚的回收率为78.2%;823K时交换一次氚的回收率就可达到66.3%.在相同温度下,氚回收率随交换次数的增加而增加,但经过6次交换后,曲线趋于平坦,氚回收率似乎在接近80%左右形成最大值.此外,单独使用氦吹洗气,氚回收率不到30%;添加0.1%的氘比氢的回收率要略高一些,这是因为充氚结束后的锂铅合金处于平衡状态,并非饱和状态,要交换出合金内的氚,必须预先吸附一定量的载带气,使其达到交换温度下的气体平衡离解压力,方可将合金中的氚交换出来.在较高的交换温度下,氚比氘、氘比氢更容易从锂铅中解析出来,这与气相色谱法分离氢同位素的原理是一致的.但过度增加载带气中氘的比例,反而降低了氚回收率,这是因为随着氘分压的增大,吸附质之间的同位素效应将减弱.总之,采用氦与0.1%氘组成的混合吹洗气,利用同位素交换效应对锂铅合金中的微量氚进行回收是有效的,氚回收效率接近80%;交换温度和交换次数对氚回收率的影响显著,在载带气相同的情况下,温度越高,交换次数越多,氚回收率越高.     

低压催化氚化亮石松碱的定位效应的研究

近年来,中草药有效成分的研究引起国内外有关学者普遍关注。氚标记中草药有效成分是研究其相应的药代动力学和代谢产物的主要手段,它具有操作简便,条件温和等优点,但是一般氚化方法均不能明确给出氚化位置。而研究氚化定位效应又是药理工作者急待解决的重要课题,所以在很大程度上限制了该项技术的使用范围。最近,郑冬珠等人用FX—100型核磁共振谱仪给出了在PdO催化剂存在条件下,低压氚化亮石松碱的氚化位置及其相对含量。本文在前文基础上,以亮石松碱为底物,根据Fraser和Garnett等人提出的氢—氚同位素交换反应动力学理论,采用CNDO/2法,对PdO催化亮石松碱的立体构型讲行了计算,得出一些有意义的结果。     

铀床氚残留量的测量

分别采用直接测量法、同位素交换法和溶解法测量铀床中的氚残留量, 并分析了这三种测量方法在本实验条件下的误差. 直接测量法测量铀床的氚残留量的结果如下: 铀床的氚残留量为2.68%, 即每克铀含(0.0308±0.0003) mmol 氚气; 当压力读数在1500～133332 Pa之间时, 基于理想气体状态方程的测量方法(简称PVT法)的标准差小于0.95%. 同位素交换法测量铀床氚的结果如下: 加热充分解吸过的铀床经多次同位素交换后, 其交换效率仅为2.84%, 即不到3%(摩尔分数)的氚被氘气载带出来, 其同位素交换法测量的标准差为7.35%. 溶解法能够彻底地测量铀床中残留的氚, 其溶解法测量的标准差为6.49%.     

在高分子负载的钯催化剂上氢-氚交换反应的研究

气-液交换法制备氚标记化合物的实质是氢-氚同位素交换,近年来国内开始引用。该法具有操作方便、快速、比度高和杂质少等优点,尤其是可标记结构复杂的天然产物如中草药有效成份。改进和完善     

疏水催化剂用于水中氚回收的实验研究

本文简要介绍了自制的几种疏水催化剂的主要特性,采用这些催化剂进行了室温下的H—T同位素交换实验,初步考察了氢气流速对催化活性的影响。实验表明,催化剂的催化活性较高,能够用于室温下从氚水中回收氚。     

锆吸氘和氚的动力学同位素效应

应用反应速率分析方法,在高真空金属系统上测定了锆在恒容体系和450～630 ℃范围内吸收氘和氚的p-t曲线。由p-t曲线可知,在同一温度下,锆吸氚的速率低于锆吸氘的速率;而随着温度的升高,由于解吸逆反应的影响,锆吸氚(氘)的反应速率降低。根据p-t曲线计算了吸气反应在不同温度的速率常数,得到锆吸氘和氚的表观活化能分别为(-25.9±0.7)和(-16.8±0.8)kJ·mol^-1。从活化能数据可以看出     

锂陶瓷氚增殖剂的中子辐照性能与产氚行为

D-T聚变堆采用氚增殖剂与中子反应生成氚来保证其燃料的“自持”。Li₂O、LiAlO₂、Li₂ZrO₃、Li₂TiO₃和Li₄SiO₄等锂陶瓷材料由于具有良好的化学稳定性、机械力学性能和产氚性能等优点,是聚变堆主要的候选产氚材料,而其在中子辐照环境下的各种性能和行为是氚增殖包层模块设计所关心的重要内容。本文介绍了国际上锂陶瓷产氚增殖剂的辐照实验研究概况,对材料的辐照性能(材料稳定性、热导性、离子电导性和活化性能等)、堆内/堆外产氚行为、影响氚在陶瓷材料中扩散或释放的各种因素,以及近来关注较多的辐照缺陷与释氚行为的相互关系等方面进行了归纳、分析和总结,同时针对中国确定的氦冷固态球床包层模块的技术路线,提出了需要广泛而系统地开展锂陶瓷基础研究的建议,指出今后国际上氚增殖剂的研究重点是高燃耗(>10%)和高荷载破坏情况下锂陶瓷材料的辐照产氚性能,以及聚变堆氚增殖包层工程条件因素,如磁场、等离子体诱发电流和中子倍增剂等对锂陶瓷小球释氚行为的影响。     

金属氧化物催化剂在不同气氛中的除氚性能

建立了惰性气氛和含氧气氛的除氚模拟系统,通过三种金属氧化物催化剂(Cu O,Ag-X和H506-2)上除氢性能的考察来优化除氚系统的工艺参数。结果表明金属氧化物催化剂在两种不同气氛下均能够高效除氢,除氢效率99%以上。在此基础上,选用H506-02为除氚催化剂,工作温度为400℃时,建立的小型除氚器可使不同气氛的原气达到深度除氚的效果。     

氚化学与工艺

氚作为一种重要的资源,在国防科技和国民经济领域有着广泛的应用。伴随着国防科技发展需求的不断提高,中国工程物理研究院在氚化学与工艺研究方面取得了一定的成就,研究领域涉及到氚的整个生命周期,包括生产、分离、储存、应用及氚废物治理等。本文重点介绍了中国工程物理研究院近年来在金属氚化物、储氚材料、氢同位素分离技术、含氚重水提氚关键技术和ITER相关氚技术等方面的研究进展。     

氚的发现及在自然界的分布

最轻的放射性核素——氚的历史,美国化学家利比(W.F.Libby)在诺贝尔奖金获得者的回忆录中,把它分为两个时期,以人类进行的第一次热核武器试验作为分界线。但合理的划分应为三个时期:第一个时期——氚的发现和物理化学特性的测定(1934—     

Synthesis of Tritium and Deuterium Labelled Agmatine

Agmatine is a promising anti-opioid dependence and relapse drug1~2 discovered and developed by Beijing Institute of Pharmacology and Toxicology, but the physiological role of agmatine in inhibition of tolerance to and dependence on opioid are not well est…     

Tritium labeling: A unique tool for studying the behavior of humic substances in living systems

A range of labeled humic substances was obtained by the tritium thermal activation method. The high specific radioactivity and radiochemical purity allowed direct determination of the hydrophobicity and surface activity of humic substances, and investigation of the behavior of humic substances in bacteria and plants.     

Efficient synthesis of acridinediones in aqueous media

An efficient synthesis of acridinediones in two steps have been achieved using water as a reaction media without chromatographic purification. First step involves the reaction of dimedone with ammonium acetate to yield enaminone in water which on further reaction with various aldehydes yields acridinedione in aqueous media. The reaction merits the use of water as solvent, no additive catalyst and provides high yield of products with good purity.     

A Simple Synthesis of Some New Arylsulfonylnitromethanes

Arylsulfonylnitromethanes were obtained by a nucleophilic substitution reaction. The suggested method of obtaining arylsulfonylnitromethanes has some important advantages over the methods known so far: It is a relatively short, one-stage process; no byproducts are obtained, so there is no need for further procedures to separate the main products from the reaction mixture; and the final compounds possess a good degree of purity. The structure of the new products were confirmed by ¹H NMR, IR, and elemental analysis. The solid state structure of 6 was established by X-ray analysis.     

Preparative synthesis of palladium(II) acetate: Reactions, intermediates, and by-products

Comparison of various laboratory procedures for the synthesis of palladium acetate demonstrated that the purest product containing no nitrite or nitrate impurities is formed in up to 90% yields upon the reaction of palladium nitrate with alkali metal acetates in aqueous acetic acid. Other laboratory syntheses are more labor-consuming and do not ensure high purity of the product. The synthesis by-products are described and possible reaction schemes are proposed.     

Efficient Procedure for Preparing Salicyl Alcohols

A new convenient procedure was developed for selective ortho-hydroxymethylation of phenols by reaction of paraformaldehyde with a mixture of phenol and orthoboric acid. The method is general for phenols containing no strong electron-withdrawing substituents; it allows preparation of o-hydroxybenzyl alcohols of high purity in a high yield.     

O-N intramolecular alkoxycarbonyl migration of typical protective groups in hydroxyamino acids

O-N Intramolecular alkoxycarbonyl (carbonate-carbamate) migration was found to occur as a common reaction of hydroxyamino acids under mild basic aqueous conditions with no formation of side products. Carbonate protective groups migrate to produce amino-protected carbamate derivatives of hydroxyamino acids with high efficiency and purity.     

Tritium in foods

The qualities of selected scintillation systems for the measurement of very low tritium content in water samples from foods were investigated in the liquid scintillation spectrometer. The influence of the parameters of the measuring method on the detection limit was defined by figures of merit. Optimum values were obtained with an emulsion system, which consists of PPO, bis-MSB, p-xylene and Triton N-101, and which takes up 40% water. 0.16 to 0.18 pCi/ml water are detectable with this system. Reference water, which is poor in tritium, was produced by combustion of propane.     

`Watching' lipase-catalyzed acylations using 1H NMR: competing hydrolysis of vinyl acetate in dry organic solvents

Lipase-catalyzed acetylations of 1-phenylethanol with vinyl acetate were monitored in situ by ¹H NMR spectroscopy. Surprisingly, even under dry conditions (no added water) the major reaction was hydrolysis of the vinyl acetate, not acetylation of the substrate. Because this competing hydrolysis consumes water and releases acetic acid, the reaction conditions in lipase-catalyzed acylations are not constant, but vary with the reaction time. Addition of a chiral shift reagent reveals the enantiomeric purity of the starting alcohol and allows calculation of the enantiomeric ratio, E, for the reaction.