Surface desorption and bulk diffusion models of tritium release from Li2TiO3 and Li2ZrO3 pebbles

The release of tritium from Li₂TiO₃ and Li₂ZrO₃ pebbles, in batch experiments, is studied by means of temperature programmed desorption. Data reduction focuses on the analysis of the non-oxidized and oxidized tritium components in terms of release limited by diffusion from the bulk of ceramic grains, or by first or second order surface desorption. By analytical and numerical methods the in-furnace tritium release is deconvoluted from the ionization chamber transfer functions, for which a semi-empirical form is established. The release from Li₂TiO₃ follows second order desorption kinetics, requiring a temperature for a residence time of 1 day (T_1dRes) of 620 K, and 603 K, of the non-oxidized, and the oxidized components, respectively. The release from Li₂ZrO₃ appears as limited by either diffusion from the bulk of the ceramic grains, or by first order surface desorption, the first possibility being the more probable. The respective values of T_1dRes for the non-oxidized component are 661 K, according to the first order surface desorption model, and 735 K within the bulk diffusion limited model.     

Li4SiO4 pebbles reduction in He + 0.1% H2 purge gas and effects on tritium release properties

Lithium orthosilicate reduction was examined by Temperature Programmed Reaction (TPR) and Temperature Programmed Desorption (TPD) methods performed in He (or Ar) + H₂ purge gas flowing through pebble bed specimens. The parameters governing the kinetics and the steady-state of the reduction process to Li₄SiO_4−x were determined at 800°C. The level x of the O-vacancy concentration at steady-state (of the order of 1.5×10⁻³ mole fraction) was found to be compatible with the impurities content in the specimens. Pebble pre-annealing treatments were found to affect the microstructure and the reduction mechanism. Post-irradiation tritium release by TPD tests were performed on both stoichiometric and reduced pebbles with similar results. Tritium release properties of this breeder system seem to be independent from the material reduction state (x).     

Fabrication of Li2TiO3 pebbles by water-based sol-gel method

Fabrication of Li₂TiO₃ pebbles by wet process received great attention for their convenience to realize mass production and good performances. Li₂TiO₃ pebbles with about 1.4 mm in diameter were prepared by a water-based sol-gel method using Ti(C₄H₉O)₄ and LiNO₃ as raw materials. This process is simple and has not been reported previously. Phase analysis, thermal analysis and morphological observation were carried out with the pebbles. The experimental results showed that a large amount of pores were presented on the surface of the pebbles and the density of the pebbles was sensitive to the sintering temperature. The pebbles sintered at 1200 °C for 10 h reached a density of ∼68%T.D. The shape of the pebbles was favorable with an average sphericity of about 1.08.     

Investigation of Stable Al2O3 Scale on Fe-Al Aluminized Coating for Tritium Barrier

It is well known that α-Al₂O₃ phase has stablility performance, high permeation reduction factor and good resistance performance in liquid LiPb, which is considered as the reference tritium barrier coating in future fusion reactor. In order to study the formation mechanism of stable α-Al₂O₃ scales on fusion structure material, the oxidation behavior of Fe-Al aluminized coating on China Low Activated Martensitic （CLAM） steel was investigated under the oxygen partial pressure from 1 Pa to 20 kPa at the temperature of 940-980 ℃. The Al₂O₃ scales were analyzed by thermogravimetric analysis meter, grazing angle X-ray diffractometer, glow discharge spectrometer, focused ion beam and transmission electron microscope. A single continuous Al₂O₃ scales with the maximum thickness of about 2 000 nm was formed on the diffusion Fe-Al aluminized layer. Thermogravimetric analysis results show that the higher oxidation rate constant is achieved while increasing the oxygen partial pressure, and then oxidation rate constant decreases. The phase transformation of Al₂O₃ scales on the surface of Fe-Al aluminized coating was studied during different oxidation time ranges from 3 min to 180 min. The metastable γ-Al₂O₃ and α-（Al0.948Cr0.052）₂O₃ phases is formed in the earlier oxidation process and finally transformed to stable α-Al₂O₃ phase. The features of the transient α-（Al0.948Cr0.052）₂O₃（113） and α-Al₂O₃（113） were detected by GXRD and then confirmed by focused ion beam and transmission electron microscope.     

Measurement of tritium production rate distribution in natural LiAlO2/HDPE assembly irradiated by D-T neutrons

A neutronics experiment was performed to measure the tritium production rate (TPR) profile in the breeder assembly with LiAlO₂ as breeder and high density polyethylene (HDPE) as neutron reflector. The breeder assembly was irradiated with 14 MeV neutrons from DT neutron generator at IPR Neutronics Laboratory. The objective of the experiment was to validate the tritium production prediction capability of the Monte-Carlo code MCNP and FENDL 2.1 data library. The tritium production rate profile in the breeding assembly was measured by irradiating Li₂CO₃ pellets kept at various locations and then tritium counting liquid scintillation technique. Experiment was analyzed with 3D Monte-Carlo code MCNP with FENDL 2.1 cross-section data library. The calculation results were found to agree with the measured tritium production rates except one point near to the source. This experiment is a starting experiment in the series of benchmark experiments for the Indian Demo breeding blanket.     

Fabrication and improvement of the density of Li2TiO3 pebbles by the optimization of a sol-gel method

Li₂TiO₃ is regarded as a promising candidate breeder in solid blanket concepts. Pebble configuration has been a preferred option due to its potential advantages in blanket design. Li₂TiO₃ pebbles were successfully fabricated by a water-based sol-gel method previously. However, the sintered density of the pebbles was very low (less than 70% theoretical density). The process parameters were optimized and the sintered density of the pebbles was improved significantly in this work. Li₂TiO₃ pebbles with density as high as 85% were obtained at a relatively lower sintering temperature (1100 °C) and shorter sintering time (4 h). The experimental results showed that the viscosity of the sol was influential to the sphericity of the gel-spheres and thus the sintered pebbles. The variety of lithium source, the pH value of the solution and the sintering conditions demonstrated significant influences on the microstructure and density of the sintered Li₂TiO₃ pebbles.     

Molecular-sieving effect of zeolite 3A on adsorption of H2, HD and D2

Synthetic zeolite 3A has the molecular-sieving windows of nominal diameter 0.3 nm in its crystal lattice framework, which obstruct the crystalline adsorption of molecules of diameter larger than 0.3 nm, except water, hydrogen and helium. The window's diameter slightly varies with temperature, however, that is endorsed in experimental results that hydrogen cannot be adsorbed at the liquid-nitrogen temperature. Authors measured the range of temperature where zeolite 3A permits hydrogen adsorption, and revealed the temperature difference of several degrees in appearance of molecular sieving for H₂ and D₂. This difference is important because from a H₂–D₂ mixture one isotope could be isolated by adsorption if operated at a temperature regulated between the molecular-sieving appearance temperatures. We have reported large values of D₂/H₂ separation factor obtained from molecular-sieving experiments. In this study, the effect of sieving for the hybrid-atomic isotope HD is examined using a H₂–HD–D₂ mixture. We here report the experimental HD/H₂ separation factor evaluated between the D₂/H₂ factor and unity. This result is significant because where the effective molecular diameter concerning the sieving mechanism is suggested. From this knowledge, the isotopic effect of sieving for HT and DT can be predicted.     

Artificial neural network modeling for fission gas release in LWR UO2 fuel under RIA conditions

A fission gas release (FGR) model was developed by using an artificial neural network method to predict fission gas release in UO₂ fuel under reactivity initiated accident (RIA) conditions. Based on the test data obtained in the CABRI test reactor and nuclear safety research reactor, the model takes into account the effect of the five parameters: pellet average burnup, peak fuel enthalpy, the ratio of peak fuel enthalpy to pulse width, fission gas release during base-irradiation, and grain size of a fuel pellet. The parametric study of the model, producing a physically reasonable trend of FGR for each parameter, shows that the pellet average burnup and the ratio of peak fuel enthalpy to pulse width are two of the most important parameters. Depending on the combination of input values for the five parameters, the application of the model to a fuel rod under typical RIA conditions of light water reactor produces 1.7-14.0% of FGR for the pellet average burnup ranging from 20 to 70 MW d/kg U.     

掺杂Cr2O3对UO2芯块烧结行为的影响

提高燃料燃耗的一个有效手段是通过增大UO₂晶粒尺寸来减少元件内部气体压力,在大晶粒UO₂芯块中,裂变气体到达晶界表面的距离增加,因而裂变气体的释放速率降低,元件内部气体压力的增高缓慢。本文研究了添加Cr₂O₃对UO₂晶粒尺寸的影响。对纯UO₂、添加0.5% Cr₂O₃及5% Cr₂O₃ 3种配方的芯块进行了试验,在5%H₂Ar保护下,以10 ℃/min和5 ℃/min的升温速率升温至1 700 ℃,然后烧结2 h或4 h,对比纯UO₂芯块与添加Cr₂O₃的芯块发现,添加Cr₂O₃可有效增大晶粒尺寸;较长的烧结时间可促进晶粒长大;较低的升温速率也使晶粒长大。烧结过程产生液相烧结,液相浸润晶粒边界,促进晶粒长大。     

Study on effects of swift heavy ion irradiation on the crystal structure in CeO2 doped with Gd2O3

To simulate the effects of Gd₂O₃-doping and high-energy fission products in UO₂, Gd₂O₃-doped CeO₂ pellets were irradiated with 200-MeV Xe¹⁴⁺ ions. Doping and irradiation effects were analyzed using X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). The lattice constant of CeO₂ decreases and the local structure is disordered with increased doping levels. However, the irradiation induces an expansion of the lattice and a disordering of atomic arrangement near the Gd atoms. The effects of the irradiation become more pronounced with increasing Gd₂O₃-dopant levels. Our results are compared with those of a study involving Er₂O₃-doped CeO₂.     

Th(NO_3)_4-UO_2(NO_3)_2-HNO_3-H_2O/30%TBP-正十二烷萃取体系主要组分分配比模型

利用文献报道的Th(NO3)4-UO2(NO3)2-HNO3-H2O/30%TBP-正十二烷体系各组分的分配比实验数据对现有的分配比模型进行分析和比对,提出了一个计算该体系各组分分配比的新模型。利用34组实验数据对新模型进行了验证,符合情况良好。计算结果表明,本文提出的模型明显优于原模型,可作为Th(NO3)4-UO2(NO3)2-HNO3-H2O/30%TBP-正十二烷萃取体系中Th(Ⅳ)、U(Ⅵ)和HNO3萃取行为计算机模拟的基础。模型建立的条件为:温度,25℃;U(Ⅵ)浓度,0~100g/L;Th(Ⅳ)浓度,0~232g/L;硝酸浓度,0~4.5mol/L。     

含TBP-HNO3超临界CO2流体静态络合萃取U3O8

建立了一种快速降低萃取系统压力的静态络合萃取实验装置。在此装置上研究了含TBP-HNO₃超临界CO₂静态络合U₃O₈的快速气化测量方法,探索了含TBP-HNO₃超临界CO₂静态络合萃取U₃O₈的行为规律。     

Blue luminescence from poly(methyl methacrylate) modified ZnO and anatase TiO2 nanocrystals prepared using γ radiation

The surface of ZnO and anatase TiO₂ nanocrystals was modified by PMMA through γ radiation. The modified nanocrystals were investigated with photoluminescence (PL) and Fourier transform infrared (FTIR) spectra. A stable blue luminescence peak (420 nm) can be observed for the modified ZnO and anatase TiO₂ nanocrystals. The intensities of luminescence of the modified ZnO and anatase TiO₂ in aqueous solution are very stable, even unchanged after storage time of one month.     

TiO2/SFP铀吸附材料的制备及其吸附性能

本工作旨在合成一种高吸附性能、高选择性的吸附材料,实现重金属离子的去除和海水中铀资源的提取。将天然葵花粉(SFP)通过溶胶凝胶法与TiO₂颗粒进行复合,得到TiO₂/SFP复合材料。将合成材料进行扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、能谱分析(EDS)、X射线光电子能谱(XPS)等表征和吸附测试;在pH值为6.0时,材料最大吸附容量可达到215.7 mg/g。复合材料对于溶液中铀的吸附符合准二级动力学模型,是一个吸热、可自发的过程,其吸附等温线符合Langmuir模型,在模拟海水中材料对铀的去除率超过90%。     

Interactions of I2 and CH3I with reactive metals under BWR severe-accident conditions

I₂ released from fuel in the event of a severe nuclear reactor accident has the ability to deposit on surfaces in the containment building. This study has focused on the reactions of I₂ with reactive metals available in the containment. The experiments have been performed under conditions similar to those in a boiling water reactor at an accident situation. Copper, zinc and aluminium showed extensive uptake of gaseous I₂ under humid conditions. Reaction rates were determined at 25, 50 and 70 °C and could be used for quantifying the effect of reactions between gaseous I₂ and copper, zinc and aluminium.Experiments with the metals placed in water showed lower I₂ uptake. Zinc iodide and aluminium iodide rapidly dissolves in water and no uptake of I₂ on these surfaces could be verified. Copper iodide has low solubility and I₂ was adsorbed on the surface.Experiments performed with reactive metals and methyl iodide showed a minor uptake of methyl iodide on zinc and aluminium in the gas phase for temperatures up to 80 °C. A continuous uptake of methyl iodide on copper was measured at 80 °C.     

α/γ相比率调控对超音速等离子喷涂Al2O3阻氚涂层微结构及性能的影响

采用超音速等离子喷涂技术在中国低活化马氏体钢表面制备不同α/γ相比率的Al₂O₃阻氚涂层,研究了α/γ相比率调控对Al₂O₃涂层微观结构、力学性能和耐电化学腐蚀性能的影响。利用掠入射X射线衍射（GIXRD）和扫描电子显微镜（SEM）表征Al₂O₃涂层的微观结构、粘结拉伸试验法和纳米压痕仪表征涂层的力学性能、动电位极化曲线法测试涂层的耐电化学腐蚀性能。研究结果显示：通过调控特征喷涂参数（CPSP）,Al₂O₃涂层中α相含量从78.6%至24.4%可控调节,且孔隙率从2.8%降低至1.5%;α相含量为78.6%的Al₂O₃涂层硬度为(11.500±0.575) GPa,约为高γ相含量(75.6%)涂层的2倍;且高α相含量(78.6%)涂层的腐蚀电流密度较高γ相含量(75.6%)涂层的腐蚀电流密度低1个数量级。以上结果表明,高α相含量(78.6%)的Al₂O₃涂层具有更优异的力学性能、耐电化学腐蚀性能以及耐Cl^-扩散穿透能力,具有应用于聚变堆结构材料表面阻氚涂层的潜能。     

The transfer of fission gas between grain faces and edges in UO2

A simple diffusion model is used to investigate the preferential motion of grain-boundary bubbles in UO₂ during high-temperature irradiation, caused by bubble-to-bubble variations in fission-gas pressure. The results are used to explain the observed development of grain-boundary porosity as irradiation proceeds, and a simple but realistic model of this process is suggested.     

Room temperature ferromagnetism of Co doped TiO2 using ion implantation and defect engineering

Ferromagnetic (FM) semiconductors obtained by doping ferromagnetic elements into a nonmagnetic semiconductor matrix are essential for the second generation of spintronics devices. In this study, we investigate Co doping behavior and subsequent magnetic properties in Co implanted and thermally annealed TiO₂. In TiO₂ single crystals, a decrease in the oxygen partial pressure during thermal annealing is found to enhance the Co substitutional fraction by increasing the concentration of oxygen vacancies. Magnetic properties determined from superconducting quantum interference device magnetometer (SQUID) measurements show that TiO₂ crystals with a large fraction of substitutional Co are ferromagnetic at room temperature. In addition to single crystals, the feasibility of Co doping via ion implantation is studied in sol–gel synthesized TiO₂ thin films. Results from grazing incidence X-ray diffraction (GIXRD) show that the implantation can produce Co doped TiO₂ thin films and that the Co incorporation into Ti lattice site accompanies the transition from rutile to anatase phase. These results show that ion beam synthesis is a useful tool for producing ferromagnetic TiO₂ with a high Curie temperature (T_C).     

离子液体中UO2(CMPO)3(NO3)2的组装及CMPO萃取铀的机理

离子液体具有独特的物理化学性质,可以参与或影响两亲分子自组装。离子液体介质中的自组装研究所涉及的两亲分子多为有机化合物,而金属配合物在离子液体中的组装鲜有报道。另外,萃取剂正辛基苯基-N,N-二异丁基胺基甲酰基甲基氧化膦(CMPO)在1-乙基-3-甲基咪唑双三氟甲基磺酰亚胺盐(C₂mimNTf²)中萃取UO₂⁺²时形成的萃合物结构组成有待深入研究。本工作探究了UO₂(CMPO)₃(NO₃)₂在C₂mimNTf²中的组装行为。原位透射电镜(原位TEM)研究表明:UO₂(CMPO)₃(NO₃)₂在C₂mimNTf²(含70μL水)中形成聚集体,冷冻刻蚀电镜(FF-TEM)显示该聚集体是胶束。此外,研究了CMPO-C₂mimNTf²体系萃取UO₂⁺²时形成的萃合物组成。离子色谱结果表明:萃取前后水相中NO^-₃浓度变化不大,电喷雾质谱(ESI-MS)上均为UO₂(CMPO)₃(NTf₂)₂的碎片离子峰,这些结果说明:CMPO-C₂mimNTf²体系萃取UO₂⁺²时形成的萃合物组成为UO₂(CMPO)₃(NTf₂)₂而非UO₂(CMPO)₃(NO₃)₂。这有助于深入了解金属配合物在离子液体中的组装行为,并对理解CMPO-C₂mimNTf²体系萃取UO₂⁺²的机理提供了重要参考。