Sound speeds in and mechanical properties of (U,Pu)O2−x

The sound speeds of longitudinal and transverse waves in the uranium–plutonium mixed oxide pellets were measured as functions of porosity, oxygen-to-metal ratio, and plutonium content. The effect of each parameter was well fitted by a linear function and the equations were obtained to calculate the sound speeds. Mechanical properties were evaluated with the sound speeds and the result of Young's modulus showed that porosity was the most important factor to decrease Young's modulus. Temperature dependence on Young's modulus was also evaluated with previously reported thermal expansion. Decrease of Young's modulus with increasing temperature was in good agreement with available literature.     

Fabrication and characterization of (U,Am)O2−x transmutation targets

A novel dust-free route for the preparation of (U, Am)O_2?x targets has been demonstrated using a combined sol–gel and single- or double Am-infiltration process at the Minor Actinide Laboratory (MALAB) of the Institute for Transuranium Elements (ITU). Samples with 10 and 20 mol% of Am were prepared. For both Am concentrations, a single cubic phase material with a fluorite structure was observed by X-ray diffraction. X-ray absorption spectroscopy was carried out to characterize the chemical state of the metal atoms and their local crystallographic environment. The U(IV) and Am(III) valence states are predominant and the O/Am ratio is ～1.6 for both Am contents. For the 20 mol% Am, EXAFS reveals an expansion of the Am–O (2.43 Å) bond length beyond the metal–oxygen bond length in both AmO₂ (2.31 Å) and UO₂ (2.35 Å).     

Measurements of O/U Ratio and Oxygen Potential for UO2+x (0≤x≲0.1)

The 0/U ratios of UO_2+x (0≤x?0.1) were determined at 1,000 and 1,200°C, using a thermobalance in atmospheres of controlled oxygen pressures set by CO/CO₂ gases. The oxygen potentials corresponding to the x values were measured in situ with a solid electrolyte oxygen sensor. For x?0.015 the present δG _{O 2} data agree well with the previously published data. In the range of 0≤x?0.015, the increasing disagreement at smaller values of x was indicated; the present δG _{O 2} values are 2 to 15 kcal/mol more negative than the prior thermogravimetric data. The results also showed that a reverse in δG _{O 2} at 1,000 and 1,200°C occurs in the range of 2.003≤O/U≤2.015. The maximum in the plot of the partial molar entropy δS _{O 2} vs. O/U ratio has consequently been found near δS _{O 2}=11 e.u. for O/U = 2.007. This δS _{O 2} value is considerably high in comparison with Markin & Bones' EMF data, suggesting a characteristic configuration of oxygen in the lattice near UO_2.007.     

Oxygen potential measurement of (Pu0.928Am0.072)O2–x at high temperatures

The oxygen potentials of (Pu_0.928Am_0.072)O_2–x were measured as a function of oxygen to metal ratio (O/M) in the temperature range from 1473 to 1873 K by the gas equilibrium method using thermogravimetry. The measured data were about 200 kJ/mol higher in the O/M ratio range from 2.00 to 1.96 and about 50 kJ/mol higher in the reducing region (below O/M ratio = 1.94) compared with those of PuO_2–x. The measured oxygen potentials were analyzed by the point defect chemistry method. From this analysis, the oxygen potential of (Pu_0.928Am_0.072)O_2–x was represented as a function of O/M ratio and temperature and calculated results were consistent with the measured data.     

共沉淀法制备(Th,U)O_(2+x)粉末工艺研究

采用共沉淀工艺制得钍铀共沉淀物(AUTh C),AUTh C经分解还原得到(Th,U)O2+x粉末。采用差热-热重分析仪分析AUTh C分解过程,多分子层吸附理论(BET)法测定(Th,U)O2+x粉末比表面积。研究p H值、氨水加入量等共沉淀反应条件对钍铀共沉淀反应影响,以及无水乙醇处理AUTh C对(Th,U)O2+x粉末比表面积影响。实验结果表明:缓慢加入碳酸铵使p H值为5.5时,钍铀均具有较高沉淀率。加入氨水使p H升至7.5以上时,能明显提高钍铀共沉淀性能,母液中残余铀浓度为89 mg/L,残余钍浓度为105 mg/L。使用无水乙醇处理AUTh C能防止分解过程中(Th,U)O2+x粉末出现硬团聚;分解终点温度为600℃下保温2 h,(Th,U)O2+x粉末比表面积达15 m2/g。     

Astrophysical S_(E2) Factor of ~(12)C(α,γ)~(16)O Reaction through ~(12)C(~(11)B,~7Li)~(16)O Transfer Reaction

<正>The ~(12)C(α,γ)~(16)O reaction is believed to be one of the most crucial reactions in nuclear astrophysics.Following the production of ~(12)C by the triple-αprocess,it strongly influences the ratio of the abundances for the main isotopes of carbon     

通过~(12)C(~(11)B,~7Li)~(16)O反应研究~(12)C(α,γ)~(16)O天体物理S_(E2)因子

正~(12)C(α,γ)~(16)O被认为是最重要的核天体物理反应之一。作为3α反应合成~(12)C后的后续反应,该反应强烈影响着宇宙中碳氧同位素(主要为~(12)C和~(16)O)的丰度比,而这两种同位素是可观测宇宙中丰度第4和第3高的同位素。本工作通过测量~(12)C(~(11)B,~7Li)~(16)O反应,导出6.917MeV 2~+阈下共振的约化α宽度,并根据约化α宽度,导出~(12)C(α,γ)~(16)O在伽莫夫窗口内的天体物理S_(E2)因子。本实验在中国原子能科学研究院的HI-13串列加速器上进行。采用束流能量为50 MeV的~(11)B束流,对~(12)C(~(11)B,~7Li)~(16)O反应~(16)O 6.917 MeV激     

Investigation of the PuO2F2 - HF - H2O system (20°C isotherm)

The PuO₂F₂ — HF — H₂O system was investigated by using the method of isomermic solubility at 20 °C. It was established that there are three phases in the sytem: plutonyl fluoride dihydrate PuO₂F₂ · 2H₂O, tetrafluoroxyplutonic acid H₂PuO₂F₄ · 4H₂O, and plutonium oxyfluoride PuO₂F₂, the composition of which was determined by chemical analysis and by using the Schreinmacher method. The chemical individuality of the phases was confirmed by electron absorption spectra. The existence of the H₂PuO₂ F₄ · 4H₂O acid was proved by using the electromigration and the potentiometric titration methods.     

ASTM C1854-17 采用惰性气体熔融-热导检测的方法测定混合氧化物((U,Pu)O_2)中氢(全部来源)的标准试验方法

<正>该试验方法包括用含铀和钚((U,Pu)O_2)的核级混合氧化物的烧结芯块测定氢含量。该试验方法是C698试验方法的一种替代方法,用于测定核级混合氧化物(MOX)烧结芯块的水分含量。试验方法C698用库仑、电解水分分析仪对混合氧化物中的水分进行检测。虽然燃料芯块中H2的主要来源是水分,但也可能有其他来源。MOX芯块C833规范对所有氢的来源进行了限     

Production of (Th,U)O2 Microspheres with Uranium Content of 0–35% by Sol-Gel Process Using CC14 as Gelation Media

Microspheres of (Th, U)O₂ with 0–40% U and with 0.3–1.3 mm diameter are produced through gelling source-sol drops in CCl₄-ammonia media, and also their characteristics are measured.

Their sphericity becomes worse with increasing U content or with decreasing colloid fraction of source sols; this is due to greater shrinkage which occurs anisotropically on the gelation. So, acceptable microspheres are obtained for U content up to 35% but not for 40% U. The shrinkage also makes microsphere surface rougher for higher U content; this is clarified by comparing their BET and geometrical surface areas and by observing them with a microscope. Their apparent and hulk densities are measured and compared. Microspheres are easily sintered up to 98% T.D. for mixed oxides but not for ThO₂; densities of the latter are scattered from 87 to 99% T.D. For all including ThO₂ with such low densities, open porosity is less than 1% T. D.     

U(NO_3)_4-HNO_3-H_2O和U(NO_3)_4-HNO_3-30%TBP-煤油体系中U(NO_3)_4,HNO_3摩尔体积的测定

为了计算U(NO_3)_4-HNO_3/30%TBP-煤油体系在萃取过程中的相体积变化,必需要有U(NO_3)_4、HNO_3在两相中的偏摩尔体积的数据。但以往人们对这个萃取体系研究得不够充分,尚无U(NO_3)_4的偏摩尔体积可供利用。     

ASTM C1853-17 采用直接燃烧红外探测法测定混合氧化物((U、Pu)O_2)烧芯块中碳(总)含量的标准试验方法

<正>该试验方法是试验方法C698的一种代替方法,用于测定核级混合氧化物燃料(MOX)烧结芯块的碳含量。在试验方法C698中碳测定方法包括在高频感应炉中用氧气燃烧MOX芯块中的碳,并通过热导池检测所产生的二氧化碳。该试验方法中碳测定包括在高频感应炉中用氧气燃烧MOX块中的碳,并利用不分散红外探测器(NDIR)对产生的二氧化碳(CO_2)进行检测。