Solid formation in simulated high level liquid waste of relatively low nitric acid concentration

Solid formation in a simulated high level liquid waste (HLLW) was experimentally examined at 2M and 0.5M nitric acid concentrations. The precipitation studies were conducted by refluxing the simulated HLLW around 100°C. Zr, Mo, Te and Ru were major precipitation elements in both 2M and 0.5M HNO₃ solutions. The amount of precipitate in 2M HNO₃ solution decreased with decreasing Zr concentration and no precipitation was found in the solution without Zr. Only about 10% of Zr, Mo and Te were precipitated, if the Mo/Zr ratio in the 0.5M HNO₃ solution was kept below 0.5. Complete removal of Zr and Mo was the most effective way to prevent solid formation in the solution with 2M and 0.5M HNO₃ concentrations.     

Formation of palladium precipitate by hydrazine in a simulated high level liquid waste

The formation of precipitates by hydrazine was experimentally examined in the simulated high level liquid waste (HLLW), which was composed of 9 elements (Nd, Fe, Ni, Mo, Zr, Pd, Ru, Cs, Sr). Palladium was precipitated over 90% above 0.05M of hydrazine concentration and at 2M HNO₃, while all of the other elements were hardly precipitated. The elements of Pd and Zr were precipitated 93% and 70% in the simulated solution in which the concentrations of Zr and Mo were decreased from 0.069M to 3.45·10^–3M and 6.9·10^–3M, respectively, and the acid concentration was decreased to about 0.5M after denitration. In a Pd solution of 0.5M and 2M HNO₃, the precipitation yield of Pd increased with hydrazine concentration and reached over 98% at 0.1M. The precipitation yield of Pd at 0.5M HNO₃ was higher than at 2M HNO₃. The Pd precipitate, formed by adding hydrazine to an acidified solution, was an amorphous compound consisting of Pd, hydrazine, nitrate and hydrate.     

New approaches to reprocessing of oxide nuclear fuel

Dissolution of UO₂, U₃O₈, and solid solutions of actinides in UO₂ in subacid aqueous solutions (pH 0.9–1.4) of Fe(III) nitrate was studied. Complete dissolution of the oxides is attained at a molar ratio of ferric nitrate to uranium of 1.6. During this process actinides pass into the solution in the form of U(VI), Np(V), Pu(III), and Am(III). In the solutions obtained U(VI) is stable both at room temperature and at elevated temperatures (60 °C), and at high U concentrations (up to 300 mg mL^?1). Behavior of fission products corresponding to spent nuclear fuel of a WWER-1000 reactor in the process of dissolution the simulated spent nuclear fuel in ferric nitrate solutions was studied. Cs, Sr, Ba, Y, La, and Ce together with U pass quantitatively from the fuel into the solution, whereas Mo, Tc, and Ru remain in the resulting insoluble precipitate of basic Fe salt and do not pass into the solution. Nd, Zr, and Pd pass into the solution by approximately 50 %. The recovery of U or jointly U + Pu from the dissolution solution of the oxide nuclear fuel is performed by precipitation of their peroxides, which allows efficient separation of actinides from residues of fission products and iron.     

Metal–metal bonding in biscycloheptatrienyl dimetal compounds of the second‐row transition metals

Density functional theory has been used to examine the dimetallocene‐like dicycloheptatrienyl dimetal compounds of the second‐row transition metals (C₇H₇)₂M₂ (M = Ru, Tc, Mo, Nb, Zr). The lowest energy (C₇H₇)₂Mo₂ structure is a coaxial structure with terminal η⁷? C₇H₇ rings, whereas the lowest energy (C₇H₇)₂M₂ structures (M = Ru, Tc, Nb, Zr) are perpendicular structures with bridging η⁴,η⁴? C₇H₇ rings except for the perpendicular (η⁴,η³? C₇H₇)₂Ru₂ structure. The metal–metal bond orders in the (C₇H₇)₂M₂ structures (M = Ru, Tc, Mo, Nb), as determined by analysis of their frontier molecular orbitals, suggest preferred 16‐ rather than 18‐electron configurations for the central metal atoms. Thus, in the coaxial (η⁷? C₇H₇)₂M₂ structures the formal bond orders are two for M = Tc and three for M = Mo. For the perpendicular structures both (η⁴,η³? C₇H₇)₂Ru₂ and (η⁴,η⁴? C₇H₇)₂Tc₂ have 16‐electron configurations with metal–metal single bonds owing to the different modes of bonding of the bridging C₇H₇ rings in the two structures. For the (C₇H₇)₂Zr₂ system the perpendicular structure has a formal Zr?Zr double bond and the coaxial structure has a very long (～3.5 Å) Zr? Zr bond indicating only 12‐ to 14‐electron configurations for the zirconium atoms.     

Separation of fission produced 106Ru and 137Cs from aged uranium targets by sequential distillation and precipitation in nitrate media

Summary Ruthenium-106 and ¹³⁷Cs have been separated from thermal-neutron irradiated UO₃ targets aged for ~2.5 years by distillation and surface interactions in nitrate media of controlled chemical composition. After digestion of the aged targets with their aluminum wrapper in 2M NaOH solution, nitric acid was added to complete dissolution of the formed residue. The prepared fission product solution was separated from ¹²⁹I and 91.8% ¹⁰⁶Ru by sequential distillation from 20% and 40% HNO₃ solutions containing H₂O₂ and KMnO₄, as oxidants, and by boiling for 4 and 2.5 hours, respectively. The recovery yield of ¹⁰⁶Ru collected in 0.1M NaOH solution was ~68.2% with a radionuclidic purity of 399.99%. Thereafter, the fission product solution was brought to pH 9.5 by addition of NaOH solution to precipitate Al(OH)₃, MnO₂, and Na₂U₂O₇ which selectively retained the remaining fission products leaving, mainly, ¹³⁷Cs in the supernatant solution. The recovery yield of ¹³⁷Cs was ≥97.3% with ~99.75% radionuclidic purity. The gamma-ray emitter contaminants which could be detected and identified in the recovered ¹³⁷Cs solution, were ~0.25% ¹³⁴Cs and ~1.4 ^. 10^-3% ^152,155Eu.     

A new method for alkaline dissolution of uranium metal foil

In order to develop a production process of ⁹⁹Mo by fission of low-enriched uranium, the first purification step, which consists of dissolution of a uranium metal foil target, was studied. It was found that alkaline NaClO gave good results, reaching the dissolution of up to 300 m of uranium foil. The different conditions for the dissolution were studied and the optimum ones were found. The influence of NaClO and NaOH concentration, temperature, dissolving solution volume per unit of surface and dissolution time were investigated. During this step, a gas, identified as H₂, was generated, and a precipitate characterized as Na₂U₂O₇ was observed. A stoichiometric reaction for this uranium dissolution is proposed.     

Chemical and electrochemical behavior of metallic technetium in acidic media

The chemical and electrochemical properties of technetium metal were studied in 1–6 M HX and in 1 M NaX (pH 1 and 2.5), X = Cl, NO₃. The chemical dissolution rates of Tc metal were higher in HNO₃ than in HCl (i.e. 8.63 × 10^?5 mol cm^?2 h^?1 in 6 M HNO₃ versus 2.05 × 10^?9 mol cm^?2 h^?1 in 6 M HCl). The electrochemical dissolution rates in HNO₃ and HCl were similar and mainly depended on the electrochemical potential and the acid concentration. The optimum dissolution of Tc metal was obtained in 1 M HNO₃ at 1 V/AgAgCl (1.70 × 10^?3 mol cm^?2 h^?1). The dissolution potentials of Tc metal in nitric acid were in the range of 0.596–0.832 V/AgAgCl. Comparison of Tc behavior with Mo and Ru indicated that in HNO₃, the dissolution rate followed the order: Mo > Tc > Ru, and for dissolution potential the order: E _diss(Ru) > E _diss(Tc) > E _diss(Mo). The corrosion products of Tc metal were analyzed in HCl solution by UV–Visible spectroscopy and showed the presence of TcO₄ ^?. The surface of the electrode was characterized by microscopic techniques; it indicated that Tc metal preferentially corroded at the scratches formed during the polishing and no oxide layer was observed.     

Preparation of 99Mo/99mTc generator based on alumina 99Mo-molybdate (VI) gel

In this work alumina ⁹⁹Mo-molybdate (VI) gel is evaluated as a column matrix for use in the preparation of small chromatographic column type ^99mTc generator. Alumina molybdate (VI) gel is prepared by dissolving inactive MoO₃ with aluminum foil in 5 M NaOH solution containing ⁹⁹Mo radiotracer. After complete dissolution, 0.5 H₂O₂ was added to the reaction mixture solution and acidified to pH 5.5 with concentrated HNO₃. The formed AlMo precipitate was washed with NaNO₃ solution, dried at 50 °C for 24 h and then packed in the form of a chromatographic column for elution of the generated ^99mTc radionuclide with physiological saline solution (0.9 % NaCl). Greater than 86 % of the generated ^99mTc activity is immediately and reproducibly eluted with passing 10 mL of the saline solution through 2.0 g of alumina ⁹⁹Mo-molybdate column bed at a flow rate of about 1.0 mL/min. The high radiochemical ≥98.6 % TcO₄ ^?, radionuclidic ≥99.90 % ^99mTc and chemical purities of the eluates satisfy the specifications for use in nuclear medicine.     

Sequential distillation of fission-produced radioiodine and radioruthenium from sulfuric acid solutions

Fission-produced ¹³¹I and ¹⁰³Ru radionuclides have been separated sequentially by distillation from H₂SO₄ of controlled chemical composition. The thermal-neutron irradiated uranium trioxide targets were digested in 2M NaOH solution and then, the supernatant solution was acidified to 20% H₂SO₄ with addition of a few drops of H₂O₂ solution. On boiling for 3.5 hours, ≥99.99%¹³¹I was volatilized, passed through 3M H₂SO₄ traps, and then collected in 0.1M NaOH + 0.01% Na₂S₂O₃ solution with a recovery yield of 73.6%. The product radionuclide had high radiochemical and radionuclidic purities. After separation of ¹³¹I, the fission-product solution was acidified to 40% H₂SO₄ acid containing KMnO₄ as an oxidant and boiled for 40 minutes. Ruthenium nuclides were volatilized and collected in 0.1M NaOH solution. Gamma-ray spectrometry showed that the separation and the recovery yields of ¹⁰³Ru were ≥99.99 and 65%, respectively, with ~92% radionuclidic purity, measured immediately after separation. The radionuclides of ¹³²I and ¹⁰⁶Rh were the main contaminants detected in the obtained ¹⁰³Ru product solution. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heterobimetallische phosphanido-verbrückte Zweikern-Komplexe - Synthese von cis-rac-[(η-C5H4R)2Zr{μ-PH(2,4,6−iPr3C6H2)}2M(CO)4] (RMe,MCr,Mo; RH,MMo)

Heterobimetallic Phosphanido-bridged Dinuclear Complexes - Syntheses of cis-rac-[(η-C₅H₄R)₂Zr{μ-PH(2,4,6-ⁱPr₃C₆H₂)}₂M(CO)₄] (R?Me, M?Cr, Mo; R?H, M?Mo) The zirconocene bisphosphanido complexes [(η-C₅H₄R)₂Zr{PH(2,4,6-ⁱPr₃C₆H₂)}₂] (R?Me, H) react with [(NBD)M(CO)₄] (NBD?norbornadiene, M?Cr, Mo) to give only one diastereomer of the phosphanido-bridged heterobimetallic dinuclear complexes cis-rac-[(η-C₅H₄R)₂Zr{μ-PH(2,4,6-ⁱPr₃C₆H₂)}₂M(CO)₄] [R?Me, M?Cr ( 1 ), Mo ( 2 ); R?H, M?Mo ( 3 )]. However, no reaction was observed between [(η-C₅H₅)₂Zr{PH(2,4,6-^tBu₃ C₆H₂)}₂] and [Pt(PPh₃)₄]. 1—3 were characterised spectroscopically. For 1—3 , the presence of the racemic isomer was shown by NMR spectroscopy. No reaction was observed at room temperature for 3 and CS₂, (NO)BF₄, Me₃NO or PH(2,4,6-Me₃C₆H₂)₂. With Et₂AlH or PhC?CH decomposition of 3 was observed.     

Hydrogen production from water decomposition by redox of Fe2O3 modified with single- or double-metal additives

Iron oxide modified with single- or double-metal additives (Cr, Ni, Zr, Ag, Mo, Mo-Cr, Mo-Ni, Mo-Zr and Mo-Ag), which can store and supply pure hydrogen by reduction of iron oxide with hydrogen and subsequent oxidation of reduced iron oxide with steam (Fe₃O₄ (initial Fe₂O₃)+4H₂↔3Fe+4H₂O), were prepared by impregnation. Effects of various metal additives in the samples on hydrogen production were investigated by the above-repeated redox. All the samples with Mo additive exhibited a better redox performance than those without Mo, and the Mo-Zr additive in iron oxide was the best effective one enhancing hydrogen production from water decomposition. For Fe₂O₃-Mo-Zr, the average H₂ production temperature could be significantly decreased to 276 °C, the average H₂ formation rate could be increased to 360.9-461.1 μmol min⁻¹ Fe-g⁻¹ at operating temperature of 300 °C and the average storage capacity was up to 4.73 wt% in four cycles, an amount close to the IEA target.     

Desorption of99Mo from spent99Mo/99mTc generator

A simple method for desorption and purification of⁹⁹Mo from spent⁹⁹Mo/^99mTc generators is described. The alumina column was washed successively with 0.9% saline water, 35% H₂O₂, and then the⁹⁹Mo was eluted with 2M NH₄OH. Ammonia and residual H₂O₂ were removed by heating the eluate. Finally,⁹⁹Mo solution was passed through a 0.2 m membrane filter to remove precipitated aluminium hydroxide.     

Dissolution of Al-Fe materials and analysis by inductively coupled plasma – atomic emission spectrometry

A technique was developed for the dissolution of Al-Fe materials containing difficult to dissolve Al₂O₃. The developed procedure uses HCl and HNO₃ for initial sample attack followed by digestion with a mixture of H₃PO₄ and H₂SO₄ at 200 °C. This procedure was employe to dissolve Al-Fe material samples before the determination of Al and Fe. Minor and trace elements (B, Cr, Cu, Mo, Si, Zr) were determined after dissolution in HCl and HNO₃. Results of a round robin study verified the procedure accuracy. The developed methods have the required accuracy and precision to be used as a quality control procedure for Al-Fe materials analysis. Received: 9 February 1998 / Revised: 1 April 1998 / Accepted: 4 April 1998     

Dissolution of Al-Fe materials and analysis by inductively coupled plasma – atomic emission spectrometry

A technique was developed for the dissolution of Al-Fe materials containing difficult to dissolve Al₂O₃. The developed procedure uses HCl and HNO₃ for initial sample attack followed by digestion with a mixture of H₃PO₄ and H₂SO₄ at 200?°C. This procedure was employe to dissolve Al-Fe material samples before the determination of Al and Fe. Minor and trace elements (B, Cr, Cu, Mo, Si, Zr) were determined after dissolution in HCl and HNO₃. Results of a round robin study verified the procedure accuracy. The developed methods have the required accuracy and precision to be used as a quality control procedure for Al-Fe materials analysis.     

Radiochemical separation of99Mo from natural uranium irradiated with thermal neutrons

⁹⁹Mo was separated from uranium and insoluble fission product hydroxides. More than 98% of⁹⁹Mo radioactivity was extracted with bis (2-ethylhexyl)phosphoric acid. The organic phase was washed and⁹⁹Mo was back-extracted from the organic phase with NH₄OH solution. The percent recovery from the organic phase was 91% and the purity of⁹⁹Mo was more than 99%. Pure^99mTc was also extracted from the organic phase with a saline solution. Reversed-phase partition chromatography was used for the purification of⁹⁹Mo from¹³¹I and other fission products (10% HDEHP on kieselguhr bed).¹³¹I and other isotopes were quantitatively eluted with 0.1M H₂SO₄,⁹⁹Mo was eluted using a mixture of 0.5 M HCl and 30% H₂O₂.     

Oxygen evolution on Ru and RuO2 electrodes studied using isotope labelling and on-line mass spectrometry

Oxide layer formation and O₂ evolution on Ru and RuO₂ films have been studied in sulphuric acid using ¹⁸O labelling together with differential electrochemical mass spectrometry (DEMS). It was shown that ¹⁶O¹⁸O is evolved from a H₂¹⁶O solution on a Ru oxide layer previously formed in H₂¹⁸O. ¹⁶O¹⁸O was also observed when oxygen is evolved on Ru¹⁶O₂ in H₂¹⁸O solution. Consequently, the oxide layer takes part in the oxygen evolution process on both types of electrode. In the case of Ru, formation of RuO₄ was observed when oxygen evolution takes place.     

The oxidative-dissolution behaviors of fission products in a Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O<Subscript>2</Subscript> solution

This study was carried out to investigate the characteristics of an oxidative-dissolution of fission products (FP) when uranium (U) is dissolved in a Na₂CO₃–H₂O₂ carbonate solution. Simulated FP-oxides which contained 12 components were added to the solution to examine their dissolution behaviors. It was found that H₂O₂ was an effective oxidant to minimize the dissolution of FP. For the 0.5 M Na₂CO₃–0.5 M H₂O₂ solution, such elements as Re, Te, Cs, and MoO₂ were dissolved with yields of 98 ± 2%, 98 ± 2%, 93 ± 2%, and 26 ± 3%, respectively, for 2 h. Among these components, Re, Te, and Cs were completely dissolved within 10–20 min without regard to the concentrations of Na₂CO₃, and H₂O₂ due to their high solubility in the carbonate solution with and without H₂O₂. However, MoO₂ was very slowly dissolved and its yield was 29 ± 3% for 4 h. The pH of the dissolved solution revealed the greatest influence on the dissolution yields of the FP, exhibiting the most effective pH condition in the range of 10–12 in order to create a considerable suppression of the co-dissolution of FP during the oxidative-dissolution of U.     

Studies on a New Material for Hydrogen Storage and Supply by Modified Fe and Fe2O3 Powder

Modified iron oxide, a new material for hydrogen storage and supply to polymer electrolyte fuel cell （PEFC）, was prepared by impregnating Fe or Fe2O3 powder with an aqueous solution containing metal cation additives （Al, Cr, Ni, Co, Zr and Mo）. Hydrogen storage properties of the samples were investigated. The results show that both Fe and Fe2O3 powder with additive Mo presented excellent catalytic activity and cyclic stability, and their hydrogen producing temperature could be surprisingly decreased. The temperature of forming hydrogen for the Fe2O3-Mo at the rate of 250 μmol·min^-1·Fe-g^-1 could be dramatically decreased from 527 ℃ before addition of Mo to 283 ℃ after addition of Mo in the fourth cycle. The cause for it was probably related to preventing the sinter of the sample particles. In addition, hydrogen storage capacity of the Fe2O3-Mo can reach w=4.5% （72 kg H2/m^3）, close to International Energy Agency （IEA） criterion. These show the value of practical application of the Fe2O3-Mo as the promising hydrogen storage material.     

Phosphido- und arsenido-verbrückte Zweikernkomplexe: Synthese und Struktur von (η5-C5H4R)2Zr{μ-P(SiMe3)2}2M(CO)4 (R = Me,M = Cr; R = H,M = Mo) sowie die Synthese von (η5-C5H5)2Zr{μ-As(SiMe3)2}2Cr(CO)4

Phosphido- and Arsenido-bridged Dinuclear Complexes. Synthesis and Molecular Structure of (η⁵-C₅H₄R)₂Zr{μ-P(SiMe₃)₂}₂M(CO)₄ (R = Me, M = Cr; R = H, M = Mo) and Synthesis of (η⁵-C₅H₅)₂Zr{μ-As(SiMe₃)₂}₂Cr(CO)₄ The reaction of (η⁵-C₅H₄R)₂Zr{E(SiMe₃)₂}₂ with M(CO)₄(NBD) (NBD = norbornadiene) yields the dinuclear phosphido- or arsenido-bridged complexes (η⁵-C₅H₄R)₂Zr{μ-E(SiMe₃)₂}₂M(CO)₄ (R = Me, E = P, M = Cr ( 1 ); R = H, E = P, M = Mo ( 2 ); R = H, E = As, M = Cr ( 3 )). No formation of dinuclear complexes was observed in the reaction of (η⁵-C₅H₄Me)₂Zr{P(SiMe₃)₂}₂ with Ni(PEt₃)₄, Ni(CO)₂(PPh₃)₂ or with NiCl₂(PPh₃)₂ in the presence of Mg. Complexes 1 – 3 were characterised spectroscopically (i. r., n. m. r., m. s.), and X-ray structure investigations were carried out on 1 and 2 . The central four-membered ZrP₂M ring is slightly puckered (dihedral angle between planes ZrP₂/CrP₂ 14.7°, ZrP₂/MoP₂ 14.2°). The Zr? P bond lengths are equivalent ( 1 : Zr? P1 2.654(4), Zr? P2 2.657(4) Å; 2 : Zr? P1 2.6711(9), Zr? P2 2.6585(7) Å), as are the M? P bond lengths (M = Cr ( 1 ): Cr? P1 2.513(4), Cr? P2 2.502(4) Å; M = Mo ( 2 ): Mo? P1 2.6263(7), Mo? P2 2.6311(10) Å). The long Zr ··· M distances of 3.414 Å (M = Cr ( 1 )) and 3.461 Å (M = Mo ( 2 )) indicate the absence of a metal-metal bond.     

EQCM Study of Ru and RuO2 Surface Electrochemistry

The present study represents comparative analysis of voltammetric and microgravimetric behavior of active ruthenium (Ru), electrochemically passivated ruthenium (Ru/RuO₂) and thermally formed RuO₂ electrodes in the solutions of 0.5 M H₂SO₄ and 0.1 M KOH. It has been found that cycling the potential of active Ru electrode within E ranges 0 V–0.8 V and 0 V–1.2 V in 0.5 M H₂SO₄ and 0.1 M KOH solutions, respectively, leads to continuous electrode mass increase, while mass changes observed in alkaline medium are considerably smaller than those in acidic one. Microgravimetric response of active Ru electrode in 0.5 M H₂SO₄ within 0.2 V–0.8 V has revealed reversible character of anodic and cathodic processes. The experimentally found anodic mass gain and cathodic mass loss within 0.2–0.8 V make 2.2–2.7 g F^?1, instead of 17 g F^?1, which is the theoretically predicted value for Ru(OH)₃ formation according to equation: Ru+3H₂O?Ru(OH)₃+3H⁺+3e^?. In the case of Ru/RuO₂ electrode relatively small changes in mass have been found to accompany the anodic and cathodic processes within E range between 0.4 V and 1.2 V in the solution of 0.5 M H₂SO₄. Meanwhile cycling the potential of thermally formed RuO₂ electrode under the same conditions has lead to continuous decrease in electrode mass, which has been attributed to irreversible dehydration of RuO₂ layer. On the basis of microgravimetric and voltammetric study as well as the coulometric analysis of the results conclusions are presented regarding the nature of surface processes taking place on Ru and RuO₂ electrodes.