新型锕系元素硼酸盐结构研究综述

近几年来,一系列新的锕系元素(钍、铀、镎、钚、镅、锔)硼酸盐化合物由硼酸熔融反应制备得到。这些化合物具有异常复杂的晶体结构以及非常优越的物理性质。硼酸钍具有纯无机多孔阳离子框架结构而拥有显著的阴离子交换性能,并能够选择性地将放射性核废液中的放射性核素99 Tc几乎完全提取出来,且保持高度的稳定性;硼酸铀化合物具有非常复杂的拓扑结构,且大部分结晶于非中心对称空间群;硼酸镎化合物经常显示出镎的混合价态,其中包含一个三重价态共存于同个化合物中的罕见例子,从而提供了一个崭新的轻锕系元素废料储放形式;硼酸钚提供了新奇的三价锕系元素配位环境;硼酸镅与硼酸锔同时显示出与硼酸钚与硼酸镧的显著差异,从而衍生出新的镧锕分离及锕系内部分离方略。迄今为止,关于超钚元素化合物的晶体结构与化学键的研究屈指可数,该系统研究具有非常显著的意义并且具有十足的挑战性。对此类化合物的进一步认识极有可能促进新一代核废料储放形式的探究及核燃料循环工艺的发展,进而阻止锕系放射性废物在环境中的扩散。     

铝合金化技术在乏燃料干法后处理中的应用研究进展

干法后处理在未来先进核燃料循环中将发挥关键作用。由美国开发的熔盐电精炼流程是目前最具应用前景的干法后处理流程之一,但是锕系元素(An)与镧系元素(Ln)的高效分离仍然是该流程目前亟待解决的关键科学与技术问题之一。研究表明,An与Ln形成铝合金时沉积电位差较大,采用固态铝电极电解有望实现An与Ln的有效分离,从而更好地服务于分离-嬗变策略。本文针对铝合金化技术在乏燃料干法后处理中的应用研究进展进行综合阐述,重点介绍铝合金化在熔盐电精炼中的应用研究,主要包括Ln和An的铝合金化行为、An和Ln的铝合金化分离等几个方面。     

Chromatographic Separation of Trivalent Actinides by Using Tertiary Pyridine Resin with Methanolic Nitric Acid Solutions

Chromatographic separation of trivalent actinides (Am, Cm and Cf) was performed by using a tertiary pyridine resin embedded in silica beads with methanolic nitric acid solutions. The trivalent actinides were eluted from the resin column in the reverse order of atomic numbers (Cf-Cm-Am). Higher concentration of methanol in the mixed solution accelerated both the adsorption of these elements on the resin and the separability for these elements. Americium was clearly separated from Cm and Cf by using a 1 cm-ø × 10 cm-height column with a 60vol% of methanol/40 vol% of concentrated nitric acid mixed solution at ambient temperature.     

The chemical reduction of neptunium to the trivalent state

It was established spectrometrically that 1–1.5 M nitric and hydrochloric acid solutions of sodium formaldehyde sulfoxylate (rongalite) reduce Np (IV) to Np (III). The reduction proceeds both in an atmosphere of nitrogen and in air, but the degree of reduction and the stability of Np (III) are increased in an atmosphere of nitrogen. It is known that an increase in the total amount of the reducing agent in the solution (hydrazine + rongalite) promotes the reduction of neptunium to the trivalent state; neptunium is reduced on the average by 70% in nitric acid solutions and by 95% in hydrochloric acid solutions.It was found that reduction of Np (V) with rongalite gave a mixture of Np (III) and Np (IV). In the Np (IV) and Np (III) mixture, the latter shows a noticeable stability to oxidation with aerobic oxygen.     

Selective adsorption of trivalent actinides from lanthanides onto activated carbons in acidic aqueous solution

Adsorption of trivalent actinides (An(III)) and lanthanides (Ln(III)) in acidic aqueous solution using activated carbons was investigated. Activated carbons exhibited significantly selective adsorption to An(III) over Ln(III) in acidic aqueous solution from about pH 1-4, independently of the starting materials, activation methods and specific surface areas.     

Sequential Ion-Exchange Separation of Heavy Elements and Selected Fission Products for Burnup Measurement

A sequential ion-exchange separation method was developed for use in burnup measurements of nuclear fuels. Group separation by anion-exchange resin column with hydrochloric acid solutions containing small amounts of nitric acid and hydrochloric acid was followed by various cation and anion- exchange processes. The heavy elements, such as U, Np and Pu, and some fission products selected as burnup monitors, such as Cs, Mo and Nd, could be sequentially and quantitatively separated from a sample taken from spent fuel. The recovery of these elements through the separation processes were examined. The sampling ratio of an aliquot in reference to the whole fuel specimen was determined by adding as sampling monitor a known amount of Cu to the sample during dissolution. The validity of the ion-exchange separation technique for routine analysis for burnup measurements is also discussed.     

水合氧化锰用于90Y发生器的制备

为探讨水合氧化锰（HMD）用于制备色谱型⁹⁰Y发生器的可行性,研究了HMD在硝酸和盐酸溶液中对Sr和Y的吸附性能。结果表明,HMD在各浓度的盐酸和硝酸溶液中均不吸附Sr ;盐酸溶液和浓度高于1 mol/L的硝酸溶液中对Y的吸附性能都较差,但在0.001~0.1 mol/L硝酸溶液中对Y的吸附性能较好。因而在低酸度的硝酸溶液中可将Sr和Y进行分离。HMD色谱柱用于Sr和Y分离时最佳高径比为5∶1;溶液的硝酸浓度为0.1 mol/L时,Sr(NO₃)₂-Y(NO₃)₃-HNO₃混合溶液通过HMD色谱柱后,超过90%的Y吸附在色谱柱上,Sr仍然保留在溶液中;色谱柱经0.1 mol/L的硝酸溶液淋洗后,再用1 mol/L的硝酸溶液可以将Y从色谱柱上洗脱,得到纯化后的Y(NO₃)₃溶液。经HMD色谱柱分离纯化的Y溶液中Sr沾污量较低。因此,HMD有望用于90Y发生器的制备。     

Solvent Extraction of Americium(VI) by Tri-n-Butyl Phosphate

Solvent extraction of Am(VI) by tri-n-butyl phosphate (TBP) from nitric acid solutions was investigated to develop a novel method for partitioning americium from high level liquid waste generated through spent nuclear fuel reprocessing. Am(VI) was prepared using ammonium peroxodisulfate and silver nitrate. The distribution coefficients of Am(VI) were determined for extraction systems of various concentrations of nitric acid and TBP. Sufficiently stable Am(VI) could be extracted and the extraction reaction of Am(VI) was found to be the same as for other hexavalent actinides. The apparent equilibrium constant varied with the concentration of peroxodisulfate used for the valence control, which was ascribed to the competitive reaction of the extraction of Am(VI) and the complex formation of Am(VI) with sulfate ion produced by the decomposition of peroxodisulfate. A distribution coefficient of Am(VI) above 1 was obtained with undiluted TBP and the separation factor between Am(VI) and Nd(III) was 87±9. TBP extraction of Am(VI), after implementing valence control, was proved to be an effective method for the partitioning of americium from fission products such as rare earth elements.     

Separation of Antimony-125 in Fission Products

Most of the known radioactive nuclides of antimony produced by neutron irradiation of uranium have fission yields below 1% and have half-lives below 60 days. An exception is ¹²⁵Sb with a half-life of 2.7 yr, which raise its relative importance among the fission products with lapse of time after irradiation, and after 1 yr of cooling, its radioactivity is no longer negligible. This circumstance has led to its being separated from such sources as fall-out. No studies have so far been reported on using the nitrate system for this separation, though it is utilized in the reprocessing of spent fuel and in the dissolution of uranium samples. The present work describes a method of separating ¹²⁵Sb from fission products with use made of silica gel—nitric acid system, and an example of its application to the separation of ¹²⁵Sb from the spent fuel of JPDR-1. The fuel was irradiated from Oct. 1963 to Sep. 1969. The amount of ¹²⁵Sb measured after separation was (1.7± O.19)×10^?1Ci/gU at June 1972.     

逆流色谱去除无机酸中痕量铀的研究

本文主要研究了以0.25 mol/L三辛基氧化膦(TOPO)的正庚烷溶液作固定相,用高速逆流色谱(HSCCC)去除市售的几种硝酸和盐酸中的铀,制备了铀含量极低的盐酸和硝酸.结果表明,纯化后酸中铀的含量均小于1 pg/mL,与超纯水及采用等温蒸发和亚沸蒸馏制得超纯酸中铀的含量相当.     

Development of a simplified separation process of trivalent minor actinides from fission products using novel R-BTP/SiO2-P adsorbents

From a viewpoint of direct separation of trivalent minor actinides (MA: Am, Cm etc.) from fission products (FP) including rare earths (RE) in high level radioactive liquid waste, the authors have developed a simplified separation process using a single column packed with novel extraction adsorbents. Attention was paid to a new type of nitrogen-donor ligand, R-BTP (2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine, R: alkyl group) as an extractant because it has higher extraction selectivity for Am(III) than RE(III). Since the R-BTP ligands show different properties such as adsorbability and stability when they have different alkyl groups, several R-BTP extraction adsorbents were prepared by impregnating the R-BTP ligands with different alkyl groups (isohexyl-, isoheptyl- and cyheptyl-BTP) into a porous silica/polymer composite support (SiO₂-P particles). This work investigated: (1) fundamental properties of the synthesized R-BTP/SiO₂-P adsorbents, (2) adsorption and desorption properties of Am and FP in nitric acid solution and water using the adsorbents in a batch experiment, (3) radiolytic and chemical stabilities of the adsorbents, and (4) the possibility for developing a simplified separation process of MA using the most promising adsorbent (isohexyl-BTP/SiO₂-P) under temperature control between 25 and 50°C.     

Adsorption mechanism of silica/polymer-based 2,6-bis(5,6-diisohexyl-1,2,4-triazin-3-yl)pyridine adsorbent towards Ln(III) from nitric acid solution

2,6-Bis(5,6-diisohexyl-1,2,4-triazin-3-yl)pyridine (isoHexyl-BTP) is a nitrogen-donor chelating ligand which shows high extraction selectivity for minor actinides (MA) over lanthanides (Ln). We synthesized a macroporous sillica/polymer-based isoHexyl-BTP adsorbent (isoHexyl-BTP/SiO₂-P) for the separation of MA(III) from Ln(III) in high-level liquid waste. The work focused on the isoHexyl-BTP/SiO₂-P adsorption mechanism towards Ln(III) in nitric acid solution and the coordination chemistry between Ln(III) and isoHexyl-BTP/SiO₂-P through batch adsorption experiments, extended X-ray absorption fine spectroscopy, acid-base titration and ion chromatography. It was found that both H⁺ and NO₃^? directly participated in the adsorption reaction. For the middle and heavy Ln(III), Ln(isoHexyl-BTP/SiO₂-P)₃(NO₃)₃·3HNO₃ was supposed as the main product of the adsorption. The Ln(III)-N (Ln(isoHexyl-BTP/SiO₂-P)₃³⁺) bond length of the first coordination layer decreased as the atomic number of Ln(III) increased, which explains the increased adsorption affinity of isoHexyl-BTP/SiO₂-P towards middle and heavy Ln(III) in relatively high concentration nitric acid as the Ln(III) atomic number increased.     

Nuclide separation from spent nuclear fuels by using tertiary pyridine resin

The newly nuclide separation system from spent nuclear fuels is proposed. The proposed separation system consists of recovery of nuclear fuel elements, separation of trivalent minor actinide from lanthanide, and separation of some fission products such as strontium. This separation system is based on the chromatographic technique using the tertiary pyridine resin. Separation experiments using mixed oxide fuel highly irradiated in fast reactor “Joyo” were carried out. The recovery of plutonium, the separation of minor actinide from fission products including lanthanides, and the separation of americium and curium were achieved. The recovery or removal of platinum group elements and technetium was also investigated, and the removal of these elements prior to the main reprocessing process has been proposed.     

裂变产物中锑的色层分离方法研究

为测定127Sb的裂变产额及衰变γ射线分支比,需研究裂变产物中锑的放化分离方法。本文研究了盐酸及硝酸溶液中Sb(Ⅲ)及Sb(Ⅴ)在Dowex 1×4、TEVA、TRU、UTEVA、硅胶等5种固相分离材料上的吸附性能,探讨了主要干扰金属离子的吸附行为,随后优化了与相关上柱、洗涤、洗脱等操作的工艺条件。依据实验结果,提出了一个硅胶和TEVA树脂联用的色层分离流程,并采用辐照铀靶溶解液进行了流程检验。结果表明,该流程对锑的化学收率大于80%,对高产额核素及干扰127Sb γ能谱测量的主要核素的去污因子均在10×103以上。该流程便于实现远程自动化操作,避免了价态调节和介质转换,且无需大量同位素载体的加入,适用于127Sb裂变产额测定中锑的放化分离,以及放化纯级127Sb制备过程中锑的初步分离。     

Evaluation study on properties of a macroporous silica-based CMPO extraction resin to be used forminor actinides separation from high level liquid waste

Basic properties of a silica-based octyl(phenyl)-N,N-diisobutylcarbamoyl-methylphosphine oxide (CMPO) extraction resin (CMPO/SiO2-P) was investigated.Adsorption behavior for some rare earth elements (RE) which are constituents of high level liquid waste (HLLW) and the long-term stability of the extraction resin in nitric acid solution were examined.The CMPO extraction resin was significantly stable in 3 mol·L?1 HNO3 solution at 50oC.Furthermore,the RE(III) were efficiently separated from non-adsorptive fission product (FP) elements such as Sr(II) in a column experiment using a highly nitric acid solution.The separation behaviors of the elements are considered to result from the difference in their adsorption and elution selectivity based on the complex formation with CMPO.There was no strong dependency of RE(III) separation efficiency on feed solution flow rate.Only from the perspectives of the acid-resistant behavior of CMPO extraction resin and the elution kinetics for the metal ions with the extraction resin,the CMPO extraction resin can be used in the modified MAREC process for HLLW partitioning.     

Extraction separation of trivalent minor actinides from lanthanides with hydrophobic derivatives of TPEN

We are developing a new MA/Ln separation process with TPEN (N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine) and its derivatives for P&T technology of HLW from spent nuclear fuel reprocessing plants. TPEN is a hexadentate ligand that has six soft-donor sites as a kind of podand type molecule and can encapsulate a metal ion. TPEN has good selectivity of Am(III) from Ln(III) and has potential to establish partitioning of MA. However, there is a serious problem for the practical application. This is to the dissolution of a slight amount of TPEN (about 10⁻⁴ mol/L) to water. High enrichment of Am(III) will be restricted by the dissolution of TPEN to water. In this study, the hydrophobicity of TPEN is improved by introducing alkyl groups and the effect of the introduction of alkyl groups on the separation of Am(III) and Eu(III) is examined. We tried to synthesize four hydrophobic derivatives of TPEN, and three derivatives were synthesized successfully. The derivatives were examined both the extractability and selectivity of Am(III) and Eu(III). One of them, tpdben, showed good selectivity and the maximum separation factor, SF_Am/Eu, was 34 at pH 5.06. A hydrophobic derivative of TPEN that has potential of application to the MA/Ln separation process was synthesized successfully.     

Separation of Precipitate-forming Elements during High Level Waste Treatment Using Acidic Zirconium Salt of Dibutyl Phosphoric Acid

Iron extraction and the limits of iron dibutyl phosphate precipitation were investigated for use in TPE/RE recovery and partitioning with the use of the acidic Zr salt of dibutyl phosphoric acid (ZS HDBP, Zr:HDBP = 1:9), dissolved in 30% TBP with Isopar-L. The presence of Mo and the solvent loading with RE affected the Fe extraction in the opposite ways. Slow kinetics and process irreversibility were found for the Fe extraction with the ZS HDBP solution. To increase acceptable Fe concentration in a HLW, reduction of Fe(III) by ascorbic acid (AA) was studied to be carried out continuously in the feed flow, just before entering the head contactor of the partitioning extraction cycle. The Mo extraction is of the same order as that of TPE and RE; so its selective stripping prior to the TPE/RE separation is required. This can be done using the DTPA or H₂O₂ solution in diluted nitric acid. The effectiveness of the process was verified by laboratory scale trials on the centrifugal contactor rig using simulated HLW. The Zr-to-HDBP ratio of 1:6 was found to be useful to decrease the Fe and Mo extractability for their better backwashing with complexants.     

ICP-MS测量超痕量钚时质谱干扰的消除及水中钚的测定

研究了感应耦合等离子体质谱(ICP-MS)测定超痕量钚时的质谱干扰及干扰元素的去除;建立了环境水样中超痕量钚的测定方法。方法所用的解吸液适于ICP-MS直接进样,并有效地消除铅等元素形成的多原子离子干扰。测量了溶液中的m／z238和2％HNO3空白液中的^239Pu和^242Pu计数率,对测量结果进行校正。方法的本底为20fg,方法对^239Pu的检出限为43fg,测定限为88fg。所分析的水样中,井水中的^239Pu含量低于检出限,地表水中^239Pu的含量高于检出限,湖水和河水中的^239Pu高于测定限,但属于全球沉降引起的本底,不会对公众造成辐射危害。     

双-丁二酰胺萃取剂对硝酸体系中Th(Ⅳ)的萃取

研究了双-丁二酰胺萃取剂的合成及其对硝酸介质中Th(Ⅳ)离子的萃取行为。从简单的原料出发,合成了新型的多官能团的双-丁二酰胺萃取剂,并以其为萃取剂、二甲苯为稀释剂,考察了水相中硝酸浓度、萃取剂浓度、盐析剂浓度等因素对Th(Ⅳ)离子分配比的影响。利用斜率分析方法提出了双-丁二酰胺萃取剂萃取Th(Ⅳ)的萃取机理。利用该萃取剂对比萃取了钍及铕离子,得到了高达166.6的分离因子。     

双-丁二酰胺萃取剂对硝酸体系中Th(Ⅳ)的萃取

研究了双-丁二酰胺萃取剂的合成及其对硝酸介质中Th(Ⅳ)离子的萃取行为。从简单的原料出发，合成了新型的多官能团的双-丁二酰胺萃取剂，并以其为萃取剂、二甲苯为稀释剂，考察了水相中硝酸浓度、萃取剂浓度、盐析剂浓度等因素对Th(Ⅳ)离子分配比的影响。利用斜率分析方法提出了双-丁二酰胺萃取剂萃取Th(Ⅳ)的萃取机理。利用该萃取剂对比萃取了钍及铕离子，得到了高达166.6的分离因子。