Fundamental studies on extraction of actinides from spent fuels using liquefied gases – Conversion of copper into nitrate with NO2 and extraction of Nd(III) nitrate by CO2 with TBP

The nitrate conversion with liquefied NO₂ and the nitrate extraction with SC-CO₂ were demonstrated for copper powder and neodymium nitrate instead of actinide compounds. Copper contacted with NO₂ in an autoclave at 353 K changed to water-soluble compounds. By XRD analysis of the product in the atmospheric condition, the formation of copper nitrate hydrate (Cu(NO₃)₂·2.5H₂O) was confirmed. As for the extraction, neodymium nitrate loaded in an autoclave was successfully extracted with the fluid of TBP and SC-CO₂ at 15 MPa, 313 K.     

The stability boundary for supercritical flow in natural-convection loops: Part II: CO2 and H2

The universality of non-dimensional parameters that govern the stability boundary of supercritical flow in natural-convection loops is examined through 146 numerical experiments. Part I reported studies of supercritical H₂O. This part extends that study to CO₂ and H₂. The finding is that the derived non-dimensional parameters appear to be valid regardless of the fluid, the geometric dimensions or the flow conditions.     

Extraction behavior of Ga(III) and Pd(II) with 2-methyl-8-quinolinol derivatives into supercritical fluid CO2

The extraction behavior of gallium(III) and palladium(II) with 2-methyl-8-quinolinol (HMQ), 2-methyl-5-hexyloxymethyl-8-quinolinol (HMO₆Q) and 5-hexyloxymethyl-8-quinolinol (HO₆Q) from an acidic solution into supercritical fluid (SF) CO₂ were investigated. Furthermore, the pH of an acidic solution contacting with SF CO₂ was spectrophotometrically measured, and the distribution constants of HMO₆Q between SF CO₂ and water were also determined at I = 0.1 M (H, Na)NO₃, 45°C, and 8.6 – 20.4 MPa. Above pH 3, the pH of the aqueous phase in contact with SF CO₂ was levelled to about 3. On the other hand, below pH 3, the pH change is negligibly small. The distribution constant (K_{D,SF CO2} of HMO₆Q between SF CO₂ and water at 20.4 MPa was about one tenth of the K_D for heptane - water system, indicating that the solubility of HMO₆Q in SF CO₂ is remarkably smaller compared with that in heptane. The Ga(III)-HMO₆Q and Ga(III)-HO₆Q complex extracted into SF CO₂ were assigned to be Ga(OH)(MO₆Q)₂ and Ga(O₆Q)₃, respectively. Palladium(II) was extracted with HMQ as Pd(MQ)₂ from a weakly acidic solution. Even in the presence of HMQ, the Pd(II)-HMQ complex extracted from the higher HCl concentration should be H₂PdCl₄.     

Treatment of UO2 pellets used for preparing fuel elements of HTR-10 followed by supercritical fluid extraction

International interest in high temperature gas-cooled reactor (HTGR) has been increasing in recent years. It is important to study on reprocessing of spent nuclear fuel from HTGR for recovery of nuclear resource and reduction of nuclear waste. Treatment of UO₂ pellets used for preparing fuel elements of the 10 MW high temperature gas-cooled reactor (HTR-10) followed by supercritical fluid extraction was investigated. When UO₂ pellets were dissolved and extracted with tri-n-butyl phosphate (TBP)–HNO₃ complex in supercritical CO₂ (SC-CO₂), the extraction efficiency was less than 7% under experimental conditions. After UO₂ pellets were ground into UO₂ fine powders, the extraction efficiency of the UO₂ fine powders with TBP–HNO₃ complex in SC-CO₂ could reach 92%. After UO₂ pellets broke spontaneously into U₃O₈ powders under O₂ flow and 600 °C, the extraction efficiency of the U₃O₈ powder with TBP–HNO₃ complex in SC-CO₂ could reach more than 98%.     

Comparison of oxidation of cast and sintered magnesium materials in CO2

Properties of oxide films formed on cast and sintered magnesium materials during oxidation in CO₂ at 793 K were examined. The compactness and the strength of oxide films were determined from film resistance to magnesium evaporation from the basic metal matrix by means of thermogravimetric measurements. The oxide films are thick, porous on Mg-Mg_O and Mg-MgF₂ materials and thin and protective on Magnox Al2 and Mg 99.99. Incompact oxide films of Mg-Zr alloys facilitate the oxygen diffusion into the underlying layer of samples. The addition of dispersed beryllium into sintered materials results in the creation of two-component films with an inner protective BeO layer. The compact oxide films are resistant to evaporation of magnesium as well as to oxidation in CO₂. The incompact and less protective oxide films are characterized by the low temperature of the beginning of magnesium evaporation.The character of oxide films was influenced by the initial surface finishing and by the dispersed phase morphology.     

Measurement of supercritical CO2 critical flow: Effects of L/D and surface roughness

The use of supercritical fluids (SCF) has been proposed for advanced power systems including advanced sodium reactors, since these fluids can provide higher thermal efficiency and reduced system component size. Data characterizing the behavior of SCF during a blowdown or rapid depressurization are essential to validate certain aspects of safety analyses. This paper describes the results of an experiment to measure the critical mass flux for numerous stagnation thermodynamic conditions, geometry and outlet tube roughness. It was found that a 1D homogeneous equilibrium model (HEM) was capable of relatively good (less than 10% error) prediction of the test data.     

Carbon deposition from a γ-irradiated CO2/CO/CH4/C2H6 gas mixture on the manganese oxides MnO, Mn3O4 and Mn2O3

The composition of oxides formed on steel surfaces within power reactors may influence heat transfer efficiency. Previous studies have indicated that carbon is deposited on spinal-type oxides containing manganese, iron, cobalt, nickel and chromium. In this investigation, characterised manganese oxides have been subjected to γ-irradiation under conditions similar to those experienced in reactors in an effort to understand the catalytic processes involved in deposit initiation and growth. Mn₃O₄ and Mn₂O₃, under the conditions present in the γ-cell, were reduced to MnO during the time of exposure. Relative carbon deposition rates were observed to follow the trend MnO>Mn₃O₄≈Mn₂O₃.     

CO2和O2地浸铀矿原液中SO2-4的快速测定

为改良现有硫酸钡比浊法测定含铀浸出液中SO^2-₄不能长时间稳定均匀地形成硫酸钡悬浊液的缺点,采用吸光比浊法研究不同波长、酸度、稳定剂、无水乙醇用量对硫酸钡分散体系稳定性的影响以提高测量准确度。实验结果表明,改良比浊法测定SO^2-₄浓度体系中的最佳实验条件为1.0 mL HCl（3 mol/L）、5.0 mL聚乙烯醇溶液(含w=10%BaCl₂•2H₂O)、3.0 mL 无水乙醇。在最佳波长440 nm处,SO^2-₄质量浓度在0.2~1.5 g/L范围内符合比尔定律。该方法的检出限为 0.003 6 mg/L,定量限为 0.012 0 mg/L（n=20）。该方法样品测量回收率为99.0%~99.8%,加标相对标准偏差为 0.63%~2.44%(n=2)。与 GB/T 5750.5-2006 国标法比较,该方法操作简便、快捷,结果准确度高,在CO₂和O₂地浸采铀浸出原液SO^2-₄浓度的测定中有广阔的应用前景。     

Study of steam, helium and supercritical CO2 turbine power generations in prototype fusion power reactor

Power generation systems such as steam turbine cycle, helium turbine cycle and supercritical CO₂ (S-CO₂) turbine cycle are examined for the prototype nuclear fusion reactor. Their achievable cycle thermal efficiencies are revealed to be 40%, 34% and 42% levels for the heat source outlet coolant temperature of 480 °C, respectively, if no other restriction is imposed. In the current technology, however, low temperature divertor heat source is included. In this actual case, the steam turbine system and the S-CO₂ turbine system were compared in the light of cycle efficiency and plant cost. The values of cycle efficiency were 37.7% and 36.4% for the steam cycle and S-CO₂ cycle, respectively. The construction cost was estimated by means of component volume. The volume became 16,590 m³ and 7240 m³ for the steam turbine system and S-CO₂ turbine system, respectively. In addition, separation of permeated tritium from the coolant is much easier in S-CO₂ than in H₂O. Therefore, the S-CO₂ turbine system is recommended to the fusion reactor system than the steam turbine system.     

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。     

Chlorination of UO2, PuO2 and rare earth oxides using ZrCl4 in LiCl-KCl eutectic melt

A new chlorination method using ZrCl₄ in a molten salt bath has been investigated for the pyrometallurgical reprocessing of nuclear fuels. ZrCl₄ has a high reactivity with oxygen but is not corrosive to refractory metals such as steel. Rare earth oxides (La₂O₃, CeO₂, Nd₂O₃ and Y₂O₃) and actinide oxides (UO₂ and PuO₂) were allowed to react with ZrCl₄ in a LiCl-KCl eutectic salt at 773 K to give a metal chloride solution and a precipitate of ZrO₂. An addition of zirconium metal as a reductant was effective in chlorinating the dioxides. When the oxides were in powder form, the reaction was observed to progress rapidly. Cyclic voltammetry provided a convenient way of establishing when the reaction was completed. It was demonstrated that the ZrCl₄ chlorination method, free from corrosive gas, was very simple and useful.     

Study on borate glass system containing with Bi2O3 and BaO for gamma-rays shielding materials: Comparison with PbO

In this work, the mass attenuation coefficients and shielding parameters of borate glass matrices containing with Bi₂O₃ and BaO have been investigated at 662 keV, and compare with PbO in same glass structure. The theoretical values were calculated by WinXCom software and compare with experiential data. The results found that the mass attenuation coefficients were increased with increasing of Bi₂O₃, BaO and PbO concentration, due to increase photoelectric absorption of all glass samples. However, Compton scattering gives dominant contribution to the total mass attenuation coefficients for studied glass samples. Moreover the half value layers (HVL) of glass samples were also better than ordinary concretes and commercial window glass. These results reflecting that the Bi-based glass can use replace Pb in radiation shielding glass. In the case of Ba, may be can use at appropriate energy such as X-rays or lower.     

Graphitization of free carbon precipitating through the reaction of UC or UC2 with N2

It has been found by X-ray diffraction that free carbon produced from reaction of UC or UC₂ with nitrogen gas is not graphite but an amorphous carbon. The degree of graphitization increases with increasing temperature and with decreasing pressure of nitrogen gas. Thermodynamic treatment of these amorphous carbons is discussed in terms of the degree of graphitization. The free energies of the amorphous carbons are calculated to be higher by about 500 cal/mol than that of graphite. Furthermore, the influence of the crystal structure of UC or UC₂ on the degree of graphitization is considered qualitatively.     

CO2+O2地浸采铀饱和树脂酸化技术与应用

介绍了CO₂+O₂地浸采铀和酸法地浸采铀的水冶回收工艺,依据新疆某地浸铀矿山的铀矿水冶工艺现状,提出将CO₂+O₂地浸采铀工艺下饱和树脂纳入酸法地浸水冶回收系统进行处理的酸化工艺。分析了CO₂+O₂浸出工艺下碳酸铀酰型饱和树脂的酸化转化机理,开展了以酸法水冶系统中淋洗剂、转型剂、洗涤合格液为酸化剂的搅拌浸泡试验。结果表明,酸法水冶系统中的洗涤合格液是符合工艺要求的酸化剂,可充分利用洗涤合格液中的剩余酸度对碳酸铀酰型饱和树脂进行转化,并将转化后树脂对铀的吸附容量由74.71 g/L提高至76.73 g/L,实现了与酸法水冶系统再饱和树脂的共同淋洗和转型。     

The stability boundary for supercritical flow in natural-convection loops: Part II: CO2 and H2

The universality of non-dimensional parameters that govern the stability boundary of supercritical flow in natural-convection loops is examined through 146 numerical experiments. Part I reported studies of supercritical H₂O. This part extends that study to CO₂ and H₂. The finding is that the derived non-dimensional parameters appear to be valid regardless of the fluid, the geometric dimensions or the flow conditions.     

Gamma irradiation effects on ZnO-based scintillating glasses containing CeO2 and/or TiO2

Irradiation resistance of as-studied scintillating glass samples were tested under the ⁶⁰Co γ-ray radiation at doses between 60 and 700 Gy. Photoluminescence properties of glasses with and without cerium ions were investigated to show the effect of cerium (III) on the luminescence of ZnO. Ultraviolet and visible optical transmittance spectra were compared before and after irradiation treatment. The so-called radiation-induced absorption coefficient (RIAC) was introduced to compare more effectively the radiation damage on glass samples. The much reduced transmittance change and decreased RIAC value in UV-Vis region indicate that the density of electron centers and hole centers caused by radiation decreased, which helps to confirm that the reduction and oxidation reaction of cerium ions took place in radiation process. From RIAC curves, it can be seen that TiO₂ enhances the irradiation resistance of sample in UV region. However, high TiO₂ content has negative effect on visible transmittance of glasses after the higher dose irradiation (700 Gy).     

Potential improvements of supercritical recompression CO2 Brayton cycle by mixing other gases for power conversion system of a SFR

A sodium-cooled fast reactor (SFR) is one of the strongest candidates for the next generation nuclear reactor. However, the conventional design of a SFR concept with an indirect Rankine cycle is subjected to a possible sodium-water reaction. To prevent any hazards from sodium-water reaction, a SFR with the Brayton cycle using Supercritical Carbon dioxide (S-CO₂) as the working fluid can be an alternative approach to improve the current SFR design. However, the S-CO₂ Brayton cycle is more sensitive to the critical point of working fluids than other Brayton cycles. This is because compressor work is significantly decreased slightly above the critical point due to high density of CO₂ near the boundary between the supercritical state and the subcritical state. For this reason, the minimum temperature and pressure of cycle are just above the CO₂ critical point. In other words, the critical point acts as a limitation of the lowest operating condition of the cycle. In general, lowering the rejection temperature of a thermodynamic cycle can increase the efficiency. Therefore, changing the critical point of CO₂ can result in an improvement of the total cycle efficiency with the same cycle layout. A small amount of other gases can be added in order to change the critical point of CO₂. The direction and range of the critical point variation of CO₂ depends on the mixed component and its amount. Several gases that show chemical stability with sodium within the interested range of cycle operating condition were chosen as candidates for the mixture; CO₂ was mixed with N₂, O₂, He, and Ar. To evaluate the effect of shifting the critical point and changes in the properties of the S-CO₂ Brayton cycle, a supercritical Brayton cycle analysis code with a properties program, which has the most accurate mixture models, was developed. The CO₂-He binary mixture shows the highest cycle efficiency increase. Unlike the CO₂-He binary mixture, the cycle efficiencies of CO₂-Ar, CO₂-N₂, and CO₂-O₂ binary mixtures decreased compared to the pure S-CO₂ cycle. It was found that the increment of critical pressure led to a decrease in cycle operating pressure ratio which resulted in a negative effect on total cycle efficiency. In addition, the effects from changed minimum operating condition and property variations of multi-component working fluid changed the recuperated heat in the cycle which was closely related to the cycle performances.     

Formation of U2C3 in the reaction of UC2 with UO2

The formation of U₂C₃ by the reaction of UC₂ with UO₂ has been studied by chemical and X-ray analyses at temperatures between 1400 and 1700 °C in vacuo. The reaction is represented by 7 UC₂ + UO₂ → 4 U₂C₃ + 2 CO.     

Compatibility of Ti3SiC2 with liquid Pb and PbBi containing oxygen

Ti₃SiC₂ is considered as a possible pump material for heavy liquid metal (HLM) cooled nuclear systems because it resists oxygen and has high temperature strength. Therefore the material was tested in stagnant lead and lead bismuth containing oxygen at temperatures between 550 and 750 °C up to 4000 h in the Karlsruher COSTA facilities. Two different oxygen concentrations (10⁻⁶ and 10⁻⁸ wt%) were chosen. During the exposure a thin TiO_x-layer was formed at the surface of the specimens. No dissolution attack was observed under these conditions.