[en] This paper reports that when a 1 mM Np(V) solution of 3 M nitric acid was irradiated by a xenon lamp with n-SiC (5 mg dm^-3) as photocatalyst and hydrazine (0.1 M) as donor, 100% of the Np(V) was reduced to Np(IV) within 30 min at room temperature. Electrochemical investigations suggested that Np(V) is reduced by the atomic hydrogen adsorbed on the photocatalyst surface. According to this mechanism, platinum group metals can act as reducing catalysts for Np(V) reduction because of their low hydrogen overvoltage. The proposed mechanism was experimentally confirmed by using platinum black (5 mg dm^-3) as catalyst and hydroxylammonium nitrate (0.9 M) as reducing agent

[en] This paper reports on homogeneous oxalate precipitation using diethyl oxalate which was compared to precipitating Pu(III) oxalate with solid oxalic acid. The diethyl oxalate technique at 75 degrees C is better because it gives 50% less plutonium in the filtrate with a reasonable filtering time. Also, the procedure for the homogeneous precipitation is easier to automate because the liquid diethyl oxalate is simpler to introduce into the precipitator than solid oxalic acid. It also provides flexibility because the hydrolysis rate and therefore the precipitation rate can be controlled by varying the temperature

[en] The dynamic behavior of carbonate ion as a ligand that interacts with the hexavalent actinyl ions of U, Np, and Pu was examined by ¹³C NMR spectroscopy. The first-order rate parameter, k, that describes the exchange between bulk solution and bound carbonate decreases with increasing pH. At a pH of 10.0, and 25 degrees C, the respective values of k for the U(VI), Np(VI) complexes are 27.1 ± 0.3, 64.7 ± 3.3, and 706 ± 29. The variation of k with temperature was used to calculate the values of activation enthalpy ΔH double-dagger = 53 and 42 kJ mol^-1; and activation entropy ΔS double-dagger = - 40 and - 71 J mol^-1 K^-1 for the uranyl and neptunyl systems, respectively. In this paper a plausible reaction scheme for the exchange reaction is considered. The influence of these slow carbonate-exchange reactions on selected electron-transfer reactions is noted

[en] Until recently plutonium dioxide was known to be among the metallic oxides most difficult to dissolve. This property is understandable given the free energy of the dissolution reaction (ΔG⁰) in acidic noncomplexing media (ΔG⁰ = 32.04 kJ/mol). Thermodynamic calculations predict that PuO₂ will dissolve under oxidizing or reducing conditions. The oxidizing dissolution, leading to Pu(VI) ion in solution, is easy to perform with a strong oxidant like Ag(II). The mechanism of the oxidizing dissolution of PuO₂ was investigated by using carbon paste electrochemistry (CPE) and ¹⁸O labeling. PuO₂ can also be dissolved in acidic solution if the redox potential of the mixture is low (e.g., Cr²⁺, V²⁺, or U³⁺ as reducing agents). The kinetics of the heterogeneous reducing dissolution of PuO₂ with Cr²⁺ were investigated and the reaction mechanism was determined by ¹⁸O labeling. In this paper all the results are presented and discussed in the context of minimizing the amount of plutonium-contaminated solid wastes in the nuclear fuel cycle

[en] The first stability constant of NpO₂⁺ with nitrilotriacetic acid (NTA) was determined at four ionic strengths (I = 0.5, 1.0, 2.0, 3.0 M) by using spectrophotometry. Nonlinear least-squares data fitting identified the complex as NpO₂NTA^2-. The specific ion interaction (SIT) theory approximation method was used to determine the stability constants at infinite dilution. In this paper first results on Pu⁴⁺ and PuO₂²⁺ complexation with NTA are reported. The stability constant for the Pu(NTA)⁺ complex at I = 0.1 M is given. From results for PuO₂²⁺ complexation with NTA (I = 1 M) at pH < 3, the stability constant was derived for PuO_2-NTA^-. At pH > 3, NTA partially reduced PuO₂²⁺ to PuO₂⁺

[en] This paper reports that abundant U⁺ ions were generated by Nd:YAG laser desorption from a uranium metal sample made by the splat technique. The stepwise reaction of U⁺ ions with 2, 4, 6,-tri-t-butylphenol (Ph'OH) initially produced a series of hydroxphenoxy-uranium ions. However, after an 800-ms reaction period at 3 x 10^-7 torr, the predominant species was the uranium triphenoxide ion, U(OPh')₃⁺. Reaction of U⁺ ions with 1, 3, 5,-tri-t-butylbenzene (Bz') showed, among other species, the molecular ion of the U(Bz')₂ sandwich compound

[en] This paper reports that neptunium and plutonium metal react cleanly with 1.5 equiv of I₂ in aprotic ligating solvents, L, to give the triiodide complexes as tetrasolvates, AnI₃L₄ [An is Np, L is tetrahydrofuran (THF) (1); An is Pu, L is THF (2a), pyridine (Py) (2b), and dimethyl sulfoxide (DMSO) (2c)]. These complexes are convenient precursors to both new and existing transuranium compounds. Reaction of the triiodide complexes 1 and 2a in hexane with 3 equiv of sodium bis(trimethylsilyl)amide provides the volatile, solvate-free tris (silylamide) complexes, An[N(SiMe₃)₂]₃ (An is Np, 3; An is Pu, 4). Hexan solutions of 3 and 4 react rapidly with 3 equiv of HO-2,6-(t-C₄H₉)₂C₆H₃ to give the aryloxide complexes An[O-26-(t-C₄H₉)₂C₆H₃]₃ (An is Np 5; An is Pu, 6). Preliminary investigations indicate that complexes 5 and 6 react with lithium bis(trimethylsilyl)methanide, Li[CH(SiMe₃)₂], in hexane to give the alkyl complexes An[CH(SiME₃)₂]₃ (An is Np, 7; An is PU, 8). Plutonium triiodide complex 2a readily reacts with LiC₅H₅ to give the known (n⁵-C₅H₅)₃Pu(THF). The homoleptic silylamide, aryloxide, and alkyl complexes are the first reported examples for transuranium elements

[en] Catalyzed electrolytic plutonium oxide dissolution (CEPOD) was first demonstrated at Pacific Northwest Laboratory (PNL) in early 1974 in work funded by the Exxon Corporation. The work, aimed at dissolution of Pu-containing residues remaining after the dissolution of spent mixed-oxide reactor fuels, was first publicly disclosed in 1981. The process dissolves PuO₂ in an anolyte containing small (catalytic) amounts of elements that form kinetically fast, strongly oxidizing ions. These are continuously regenerated at the anode. Catalysts used, in their oxidized form, include Ag²⁺, Ce⁴⁺, Co³⁺, and AmO₂²⁺. This paper reviews the chemistry involved in CEPOD and the results of its application to the dissolution of the Pu content of a variety of PuO₂-containing materials such as off-standard oxide, fuels dissolution residues, incinerator ash, contaminated soils, and other scraps or wastes. Results are presented for both laboratory-scale and plant-scale dissolves

[en] This paper reports on a study of the structural and thermal aspects of alkali metal double sulfates of plutonium has led to a new chemical assay standard for plutonium, K₄Pu(SO₄)₄. The compound is obtained by dehydration of the dihydrate, K₄Pu(SO₄)₄ · 2H₂O. Anhydrous K₄Pu(SO₄)₄ was evaluated for its purity, solubility, stoichiometry, and stability for a 2-year period. Chemical analyses for plutonium and sulfate and emission spectrographic and mass spectrometric analyses for impurity elements showed that the compound is stoichiometric, with a total impurity content of less than 250 ppm. Analysis for plutonium in store samples confirmed that the product is stable to α-radiolytic and atmospheric conditions and that it decomposes only above 700 degrees C. The evaluations done on preparations of up to 100 g per batch favor its selection as a better chemical assay standard for plutonium than Pu(SO₄)₂·4H₂O

[en] This paper reports that laser resonance ionization mass spectrometry has been investigated as a method for the detection of trace amounts of neptunium and plutonium. The instrument consists of three tunable pulsed dye lasers pumped by one or two copper vapor lasers and a time-of-flight spectrometer. High selectivity can be achieved by three-step photoionization. Measurements of the isotopic ratios of plutonium yielded a good agreement with mass spectrometric data. By saturating the excitation steps and by using autoionizing states for the ionization step, a detection efficiency of 4 x 10^-6 has been determined for plutonium, corresponding to a detection limit of less than 10⁷ atoms. Electrophoretic ion focusing enable s the separation of oxidation states of neptumiun and plutonium. The combination of this analytical technique with radiometric detection method or laser resonance ionization mass spectrometry allows the speciation of neptunium and plutonium at very low concentrations