Solubility of Uranyl Nitrate Precipitates with N-Alkyl-2-pyrrolidone Derivatives (Alkyl = n-Propyl,n-Butyl,iso-Butyl,and Cyclohexyl)

The solubility of UO₂(NO₃)₂(NRP)₂ (NRP = N-alkyl-2-pyrrolidone) in aqueous solutions with HNO₃ (0–5.0 M) and the corresponding NRP (0–0.50M) has been studied. As a result, the solubility of each speciesof UO₂(NO₃)₂(NRP)₂ generally decreases with increasing concentrations of HNO₃ and the corresponding NRP (C _HNO3 and C _NRP, respectively) in the supernatant. The solubility of UO₂(NO₃)₂(NRP)₂ also depends on the type of NRP; a higher hydrophobicity of NRP generally leads to a lower solubility of UO₂(NO₃)₂(NRP)₂. The logarithms of effective solubility products (K _eff) of UO₂(NO₃)₂(NProP)₂, UO₂(NO₃)₂(NBP)₂, UO₂(NO₃)₂(NiBP)₂, and UO₂(NO₃)₂(NCP)₂ at different C_HNO3 values and 293K were evaluated. For instance, at C_HNO3 = 3:0 M, logK ^NProP _eff = ?1:07 ± 0:03, log K ^NBP _eff = ?2:23 ± 0:02, log K ^NiBP _eff = ?2:59 ± 0:03, and log K ^NCP _eff = ?3:80 ± 0:05. The solubility of UO₂(NO₃)₂(NRP)₂ is determined by the balance among the common-ligand effect, ionic strength, and variation of log K _eff with C _HNO3.     

Reactivity of Monochlorobenzene and Its Derivatives toward Solvated Electrons in Lower Aliphatic Alcohols

Monochlorobenzene and its para- or meta-substituted derivatives were irradiated with -γ-rays in methanol, ethanol and n-propanol containing nitrous oxide to elucidate the reactivities of these organic solutes toward solvated electrons, and also the effect of the substituent for the aromatic nucleus on the reactivities of these solutes. The value of G (N₂) is seen to decrease with increasing concentration of the organic solute. Relative rate constants of these organic solutes toward solvated electrons have been determined from the competition with nitrous oxide by observing the G(N₂) in there systems. Based on the results, the rate constants of the reactions of these derivatives of monochlorobenzene with solvated electrons relative to monochlorobenzene can be related to Hammett's σ function. The ρ value has been observed to be 3.3, 2.1 and 1.8 for methanol, ethanol and n-propanol respectively. The present data, together with that by Sherman⁽¹⁾ for 2-propanol, indicates that the ρ value is correlated linearly to the dielectric constant of the solvent. Some discussions are presented on the results thus obtained.     

The Uranium-Carbon-Nitrogen System

In the previous work⁽¹⁾ dealing with the equilibrium phase relations in the ternary system U-C-N, a qualitative phase diagram was constructed from thermodynamical calculations and experiments. In the thermodynamical calculations, it was assumed that the free energy of formation of the solid solution between UC and UN, i.e., UC_1-x N _x , is the sum of (1-x)ΔG ⁰(UC), xΔG ⁰ and a term for the entropy of mixing RT{x logx+(1-x)log(1-x)}, neglecting the heat of mixing.

The purpose of the present work is to consider the same U-C-N system statistico-thermodynamically, and to evaluate the heat of mixing from the results of several experiments. A value of about ?1.3 kcal/mole was obtained as the heat of mixing corresponding to {2φ(C-N)-φ(C-C)-φ(N-N)}N, where φ(C-N), φ(C-C) and φ(N-N) are the bond energies of C-N, C-C and N-N respectively.     

Sorption and Colloidal Behavior of Np(IV) in a Bentonite-Carbonate Solution System

Abstract

Sorption of Np(IV) on bentonite in the presence of carbonate was studied by a batch method. The sorption was considered mainly due to Np(OH)₂(CO₃)₂ ^2- and Np(OH)₄(CO₃)₂ ^4- The distribution coefficient (K_d of Np(OH)₂(CO₃)₂ ^2- and Np(OH)₄ (CO₃)₂ ^4- was determined to be 10^4.01±0.24 ml/g and 10^3.93±0.37 ml/g respectively. The increasing K_d at high pH was attributed to the sorption of NpO₂(OH)_-2 with the K_d of 10^5.82±0.39 ml/g

The formation of colloidal species was observed under a reducing condition. By assuming Np(OH)₄ as the colloidal species, the formation constant was evaluated to be β_c≤10^53.85 Under an oxidizing condition, the formation of the colloidal species was less observed possibly due to the transformation of Np(OH)₄ to NpO₂OH.     

Structural and Electrochemical Studies on Uranium(VI) Nitrato Complex with n-Octyl(phenyl)-N,N-Diisobutylcarbamoylmethylphosphine Oxide in Non-aqueous Solvents

The structure of uranyl nitrato complex with CMPO [n-Octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide] in solid state and in non-aqueous solvents without containing free CR/IPO has been studied by using IR spectrophotometer, ¹³C- and ³¹P-NMR. The carbonyl(vcO) and phosphoryl(vpO) stretching bands of coordinated CMPO were observed at lower wavenumber than the corresponding bands of free CMPO in both the states. The ¹³C and ³¹P peaks assigned to the carbonyl carbon and phosphoryl phosphine of coordinated CMPO was detected in the lower field than that of free CMPO. From these results, it was concluded that the uranyl nitrato complex with CMPO in both the states has the structure with two nitrate and one CMPO coordinated as bidentate in the equatorial plane of uranyl ion, i.e., UO₂(NO₃)₂·CMPO. Furthermore, the electrochemical studies of UO₂(NO₃)₂·CMPO complex in CH₃CN have been carried out using cyclic and normal pulse voltammetric methods. It was found that the UO₂(NO₃)₂·CMPO complex is reduced to U(V) complex at around ?1.22V vs. Fc/Fc⁺ (ferrocene/ferrocenium) and that the resulting reductant is oxidized to U(VI) at around +0.04V vs. Fc/Fc⁺.     

Solvent Extraction of Pentavalent Neptunium with n-Octyl(phenyl)-N,N-Diisobutyl- carbamoylmethylphosphine Oxide

Solvent extraction of Np(V) from HNO₃ solution was experimentally studied with n-octyl(phenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO) as an extractant mixed with TBP and n-dodecane. In the low HNO₃ concentration, the Np(V) is weakly extractable, but effectively extracted in the high HNO₃ concentration (>4M) due to the disproportionation of Np(V) to Np(IV)and Np(VI). The distribution ratio of Np was increased by use of H₂O₂as a reductant of Np(V). More than 95% of Np was extracted with 0.8 M H₂O² in 2.2 M HNO₃ solution. It was shown that most of the Np extracted is in tetravalent state as expected from redox mechanism. The Np(IV) extracted in the organic phase was effectively stripped to the aqueous phase with H₂C₂O₄.     

EPR Study of Uranium (V) Species in Photo-and Electrolytic Reduction Processes of UO2 NO3)2-2TBP

Abstract

Electron Paramagnetic Resonance (EPR) and optical spectra of uranium(V) species were observed in both processes of photo- and electrolytic reduction of UO₂(NO₃)₂-2tributylphosphate (TBP) in 80%TBP-n-dodecane solution. The formation of U(V) species was detected by an optical spectrum (λ_max: 770, 970 and 1,420 nm). EPR signal with the value of ff-factor –2.3 and a linewidth of approximately 1,100 Gs was observed during the electrolytic reduction. On the other hand, during the photoreduction the signal with the value of fil-factor –1.94 was observed and there was found a superhyperfine structure with the intensity ratio of 1:2:1, that is caused by the superhyperfine coupling with nuclear spin, I=1/2, of the strongly coordinated ³¹P to the central uranium through oxygen atom. The superhyperfine coupling constant was estimated to be 27 Gs. Moreover, the signal with the value of g-factor –2.00 due to an organic radical was observed. The residue after the thermo-gravimetric analysis of UO₂(NO₃)₂-2TBP was identified as α-UP₂O₇ by the powder X-ray diffraction analysis, indicating the strong coordination of TBP to the central uranium atom.     

Thermal decomposition kinetics of ammonium uranyl carbonate

The thermal decomposition kinetics of AUC [ammonium uranyl carbonate; (NH₄)₄UO₂(CO₃)₃] in an isothermal thermogravimetric (TG) reactor under N₂ atmosphere has been determined. The kinetic data can be represented by the two-dimensional nucleation and growth model. The reaction rate increases and activation energy decreases with increasing particle size and precipitation time which appears in the particle size larger than 30 μm in the mechano-chemical phenomena.     

A study on selective precipitation ability of cyclic urea to U(VI) for developing reprocessing system based on precipitation method

We have proposed a new reprocessing system based on precipitation method. In order to find out precipitants with high selectivity to U(VI) and to investigate factors controlling precipitation ability to U(VI) and U(IV), properties of 3,4,5,6-tetrahydro-1,3-dimethyl-2(1H)-pyrimidinone (DMPU) as a precipitant have been examined by using U(VI), U(IV) as a simulant of Pu(IV), and simulated fission products (FPs). We have evaluated precipitation ratios (P.R.) for U(VI) and U(IV), solubility of U(VI) precipitates to 3.0 mol dm^?3 (M) HNO₃ solution, melting points (MPs) of U(VI) precipitates, log P (distribution ratio of a substance in 1-octanol/water biphasic system, a measure of hydrophobicity) of precipitants, and decontamination factors (DFs) of FPs. The properties of DMPU were compared with those in systems using N-n-butyl-2-pyrrolidone (NBP), N-cyclohexyl-2-pyrrolidone (NCP), and other pyrrolidone derivatives as the precipitant. The P.R. values of DMPU to U(VI) and U(IV) in 3.0 M HNO₃ solutions were around 99% at [DMPU]/[U(VI)] = 2.0 and 0% at [DMPU]/[U(IV)] = 5.0, respectively. In DMPU system, the DF values of the most of simulated FPs [Rb(I), Cs(I), Sr(II), Ba(II), Ru(III), Rh(III), La(III), Ce(III), Pr(III), Nd(III), and Sm(III)] used in the present study were found to be more than 100. Even in U(VI)–U(IV) coexisting system, the selectivity of DMPU to U(VI) was higher than those of NBP and NCP. This selective precipitation ability of DMPU to U(VI) was evaluated by the solubility of U(VI) precipitates on the basis of their MPs and the log P values of precipitants. As a result, it was found that the precipitants having low hydrophobicity and forming the U(VI) precipitates with high MPs have highly selective precipitation ability to U(VI).     

Calculations of Reduced Partition Function Ratios of Hydrated Boric Acid Molecule by the ab initio Molecular Orbital Theory

Based on the ab initio molecular orbital theory at the HF/6-31G(d) level, the effect of hydration on the reduced partition function ratio (RPFR) of the boric acid molecule (B(OH)3) was evaluated in order to better understand boron isotope fractionation observed in aqueous systems. The B(OH)₃(H₂O) _n species with n up to 12 were considered and their geometry optimization and RPFR calculations were carried out. It was induced that hydration decreased the RPFR of B(OH)3 and the degree of decrease in ln(RPFR) was ca. 1.5%, which was nearly equivalent to that of B(OH)₄ ^-.     

Group Type Analysis of Carboxylic Acids Formed by Degradation of i-Dodecane and Kerosene with Nitric Acid

Quantitative analysis of carboxylic acids formed by diluent degradation with nitric acid was investigated by group type analysis.

Based on Beer-Lambert's law and alkaline titration, the apparent molar extinction coefficient (E^a _max) for C=0 stretching vibration (v _c=0: 1,694 cm^?1) of carboxylic acids in degraded diluents was determined to be 620±20 mole^?l·/·cm^?1. Using this value, the concentrations of carboxylic acids formed under various nitric acid concentrations, temperatures and contact times were determined, and some of the results were compared with the measured data from alkaline titration.

The method might also be used to determine the concentration of carboxylic acids hydrogen-bonded with tri-n-butyl phosphate (TBP) in degraded solvent.     

Selectivity of Alkali Metal Ion and Lithium Isotopes on Ion Exchangers in H Form Prepared from LiTi x Zr2-x (PO4)3 (x=0, 1)

Inorganic metal (IV) phosphate-based ion exchanges in the hydrogen form, HTi _x Zr_2-x (PO₄)₃ (x =0, 1), have been prepared by leaching lithium ions from the precursors, LTi _x Zr_2-x (PO₄)₃ (x=0, 1), through ion exchange with protons. The degrees of leaching of lithium ion were more than 99%. Both ion exchangers showed high selectivity toward lithium and sodium ions and little affinity to rubidium and cesium ions among alkali metal ions. The lithium ion uptakes from aqueous solutions were monotonously increasing functions of pH. Isotopically, both ion exchangers were ⁶Li-specific like other inorganic ion exchangers so far examined. The ⁷Li-to-⁶Li isotopic single-stage separation factor, S, of HTiZr(PO₄)₃ was larger than that of HZr₂(PO₄)₃ at a given pH-value. The relatively large S-values of 1.022 and 1.042 were found for HZr₂ (PO₄)₃ for HTiZr(PO₄)₃, respectively, at 25°C when the pH of the solution phase was around 5.     

Carbonate Complexation of Np(VI) in Near-Neutral Solutions

Abstract

A spectroscopic study of Np(VI) was performed in carbonate solutions. The characteristic absorption bands were observed at 625, 670 and 703 nm and examined for the dependence on pH and carbonate concentration. The absorbances showed no dependence on pH but proportionally increased with the increasing carbonate concentration. From the observations, the result was analyzed by considering the reaction of NpO₂(OH)2_(s)+CO₃ ^2-=NpO₂ (OH)₂CO₃ ^2-. By measuring the solubility, the equilibrium reaction constant was calculated to be log K=- 2.49±0.15. The stability constant of NpO₂(OH)₂CO₂ ^2- was predicted to be log β= 20.21±0.15 by taking the literature value of solubility product of NpO₂ (OH) _2(s).     

Generalized Synthetic Kernel Approximation for Elastic Moderation of Fast Neutrons

A method of synthetic kernel approximation is examined in some detail with a view to simplifying the treatment of the elastic moderation of fast neutrons. A sequence of unified kernel {f _N } is introduced, which is then divided into two subsequences {W _n } and {G_n} according to whether N is odd (W _n =f _2n-1, n=1, 2,…) or even (G _n =f _2n , n=0,1, …). The W ₁ and G ₁ kernels correspond to the usual Wigner and GG kernels, respectively, and the W _n and G _n kernels for n ≧ represent generalizations thereof. It is shown that the W _n kernel solution with a relatively small n (≧2) is superior on the whole to the G_n kernel solution for the same index n, while both converge to the exact values with increasing n. To evaluate the collision density numerically and rapidly, a simple recurrence formula is derived. In the asymptotic region (except near resonances), this recurrence formula allows calculation with a relatively coarse mesh width whenever h_a ≧0.05 at least. For calculations in the transient lethargy region, a mesh width of order ?/10 is small enough to evaluate the approximate collision density φ _N with an accuracy comparable to that obtained analytically. It is shown that, with the present method, an order of approximation of about n=7 should yield a practically correct solution diviating not more than 1% in collision density.     

A Nuclear Magnetic Resonance Study on Ligand Exchange Reactions in La(III), Nd(III), and U(VI) Nitrato Complexes with n-Octyl(pheny1)-N,N-Diisobutylcarbamoylmethylphosphine Oxide in Non-aqueous Solvents

The exchange reactions of n-octyl(pheny1)-N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in La(III), Nd(III), and U(VI) nitrate complexes with CMPO (La(III)-, Nd(III)-, and U(VI)-CMPO complexes) have been studied in CD₃COCD₃ by means of ³¹P NMR method. The number of CMPO coordinated to the first coordination sphere of La(III) ion was directly determined to be 3 by the area integrations of ³¹P NMR signals of free and coordinated CMPO molecules. The same coordination number of 3 was also obtained for the U(VI)-CMPO complex. The coordination number was not determined for the Nd(III)-CMPO complex, because of its paramagnetic behavior. The exchange rate constants of CMPO in La(III)- and U(VI)- CMPO complexes were obtained by the two-site exchange model. Paramagnetic line broadening was observed in the Nd(III)-CMPO complex and the rate constant for the exchange of CMPO was determined by the line-broadening method. The exchange rates of CMPO in La(III)- and Nd(III)-CMPO complexes depend on the free CMPO concentration ([CMPO]), while that in U(VI)-CMPO complex is independent of [CMPO]. The dissociative (D) and dissociative interchange (I_d ) mechanisms were proposed for the exchange reactions in the La(III)- and Nd(III)-CMPO complexes, and dissociative (D) or I_d mechanism was proposed for the U(VI)-CMPO complex. The dissociative rate constants (s^?1) at 25°C and activation parameters ΔH^# (kJ·mol^?1) and ΔS^# (J·K^?1·mol^?1) are 4.76x10³, 28.7±0.1, ?78.4±0.2 for La(III)-CMPO complex, 4.72x10³, 42.6±0.4, ?31.7±1.3 for Nd(III)-CMPO complex, and 3.20x10³, 46.9±0.6, ?20.5±2.2 for U(VI)-CMPO complex, respectively.     

Research of Radioisotope Production with Fast Neutrons, (VII)

Production of radioisotopes of high specific activity was studied in the JRR-1 reactor using several (n,p) and (n,α) reactions, such as ²⁴Mg(n,p)²⁴Na, ²⁷A1(n,α)²⁴N_a, ³⁵Cl(n,p)³⁵S, ³⁵C1(n,α)³²P, ⁵⁸Ni(n,p)⁵⁸Co, ⁶⁴Z_n (n,p) ⁶⁴C_u and ⁶⁷Z_n(n,p) ⁶⁷Cu. The target materials for these reactions were irradiated in several experimental holes of JRR-1 and the radioisotopes formed in the target materials were separated. The amount of the radioisotopes produced and the specific activity were determined, and the possibility of producing high specific activity radioisotopes by these reactions was investigated. The specific activity of the radioisotopes produced by the (n,p) and (n,γ) reactions was more than several hundreds times higher than when produced by the corresponding (n,γ)reactions. Although the yield of the radioisotopes by the former two reactions was fairly small, practical production of high specific activity radioisotopes by this method was thought to be possible, at least for elements of lower atomic number such as those studied in the present work.

For each experimental hole, the thermal and the fast neutron fluxes were determined respectively by the reactions ¹⁹⁷Au(n,γ)¹⁹⁸Au and ⁵⁸Ni(n,p)⁵⁸Co. In order to apply these (n,p) and (n,α) reactions effectively to radioisotope production, such basic informations as the dependence of the reactions on neutron energy and the effect of irradiation position on the reaction yield were studied on the basis of the neutron flux distribution, and the cross section of the reactions for fast neutrons in JRR-1 was estimated.     

Enhancement of the Mutual Separation of Lanthanide Elements in the Solvent Extraction Based on the CMPO-TBP Mixed Solvent by Using a DTPA-Nitrate Solution

The mutual separation behavior of rare earth elements was studied in the system based on the neutral extractant CMPO (n-octyl(phenyl)-N,N-diisobutylcarbamoyl methylphosphine oxide) and aminopolyacetic acid DTPA (diethylenetriamine pentaacetic acid). The extractability of lanthanides decreased monotonously with increasing of atomic number in the system of 0.2 M CMPO-1.0 M TBP-n-dodecane (TRUEX solvent) and 0.05 M DTPA-NaNCO₃ or hydroxylamine nitrate (HAN) solution. The separation factor of La/Lu was 6,600 using 0.05 M DTPA-3M NaNO₃ solution (initial pH=2.0). The mutual separation of lanthanides in the CMPO/DTPA system was greatly improved when compared with the general TRUEX system. The separation factor was not affected by the initial pH of the solution (1.8–2.2), the salting out reagent (NaNO₃ and HAN), or its concentration (2, 3 M). The experimentally obtained separation factors of lanthanide elements were reproduced by a simple model based on the distribution ratios in the TRUEX extraction system and the stability constants of DTPA-metal complex. The mutual separation between light lanthanides is attributed to the selectivity of DTPA, while CMPO mainly influences the separation of heavy lanthanides.     

Photochemical Reaction of Bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato) (tetrahydrofuran)dioxouranium(VI) in Supercritical Carbon Dioxide

The emission lifetime of bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)(teterahydrofuran)dioxouranium(VI) complex, UO₂(hfac)₂thf, has been measured in sub and supercritical carbon dioxide (sc-CO₂) under the conditions of 10 to 60 MPa and 293.2 to 340.2 K. It was found that the decay rate constants of excited UO₂(hfac)₂thf species (*UO₂(hfac)₂thf) decrease with increasing the pressure of sc-CO₂. The rate constants for quenching reactions of *UO₂(hfac)₂thf with alkenes in sc-CO₂ were determined as 4.32×10⁹(for cyclohexene), 3.04×10⁹(for cycloheptene), 2.13×10⁹(for 1-octene), and 3.801×10⁸mol^-1·dms^-1·s^-(for 1-hexene). The activation volumes for the quenching reactions of *UO₂(hfac)₂thf with cyclohexene, cycloheptene, 1-octene, and 1-hexene at 308.2 K were determined to be 16.7, 28.7, 16.7, and 24.7cm³.mol^-1, respectively.     

Flow in Low Pressure Impactor and Collection Efficiency of Particles

An effect of specimen size on the Charpy impact property was evaluated in the ferritic-martensitic 11Cr-0.5Mo-2W, Nb, V stainless steel (PNC-FMS). The upper shelf energy (USE) is expressed by the power law equation as USE[J]=m(Bb) ⁿ where m is the material constant (m=0.277 in PNC-FMS), B[mm] is the specimen thickness and b[mm] is the ligament size. The normalizing exponent n was empirically derived using the USE of the full size specimen as n=1.38×10^–3USE_full+1.20. The n value varies in the range of 1.2 to 1.7, which is affected by the fracture volume below the notch. The PNC-FMS wrapper takes n=1.42. The ductile-to-brittle transition temperature (DBTT) of PNC-FMS is correlated as DBTT=115(log₁₀ BKt)—158 using an elastic stress concentration factor Kt that represents the effects of notch size, e.g. notch depth, notch root radius and notch angle.     

Investigation of the infinite medium integral neutronic data for incident fusion source neutrons

In the present work, the physical behavior of integral data in infinite medium has been evaluated for incident fusion neutrons with the help to the 3-D Monte Carlo code. In a fusion reactor blanket with finite dimension, the integral quantities will be more or less different from the infinitive medium results, depending on the neutron leakage fraction. Design studies foresee the reduction of the neutron leakage out of the blanket as possible in order to prevent the nuclear heating in super conducting fusion magnets and to keep all neutrons primarily in the coolant. The most important materials in fusion technology, namely tritium, beryllium, lead, thorium, and uranium have been investigated in infinitive medium. The main purpose of this work is to calculate the integral tritium breeding ratio, ²³³U breeding rate, ²³⁹Pu breeding rate, heat release, neutron multiplication ratio through (n,x) and fission (when applicable) reactions in those mixtures which are composed when first UO₂ and ThO₂ are mixed with natural lithium (Nat.Li) or ⁶Li for a volume fraction from 0 to 100%. Then the variable UO₂-Nat.Li (UO₂ mixed with Nat.Li) and UO₂-⁶Li (UO₂ mixed with ⁶Li) compositions will be mixed with Beryllium (Be) and Lead (Pb) for a volume fraction from 0 to 100%. However, the variable TO₂-Nat.Li (ThO₂ mixed with Nat.Li) and ThO₂-⁶Li (ThO₂ mixed with ⁶Li) compositions will be mixed with Be and Pb for a volume fraction mentioned above.