Use of redox reagents for stabilization of Pu and Np valence forms in aqueous reprocessing of spent nuclear fuel: Chemical and technological aspects

Marchenko, V. I.; Dvoeglazov, K. N.; Volk, V. I.

doi:10.1134/s1066362209040018

Cited by 35 publications

(28 citation statements)

References 39 publications

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“…The rate of this reaction is comparable with the rate of the reduction with the most kinetically effective reductants of the class of organic derivatives of hydrazine, hydroxylamine, and oximes, which are considered as alternatives to traditional reagents for Pu stripping [1]. Calculation based on the results of this study and on data of [10,11] shows that, at [HNO 3 ] = 1 M and 35°С, the time of 99% reduction of Pu(IV) is 1.3, 3.7, 1.3, and 1.1 min with carbohydrazide, hydroxyethylhydrazine, acetaldoxime, and dimethylhydroxylamine, respectively (at reductant concentration of 0.5 M).…”

Section: Use Of Carbohydrazide For Stabilizing Desired Combinations Omentioning

confidence: 99%

“…1 We attempted to stabilize the Pu(III)-Np(V) couple at 35°C in a 1.1 M HNO 3 solution containing (M) 0.012 Pu(IV), 2.1 × 10 -3 Np(VI), and 0.2 (NH 2 NH) 2 CO. As seen from Fig. 6, Pu(IV) is very rapidly (within less than 1 min) reduced to Pu(III), whereas Np(VI) is reduced to Np(V) more slowly that it was expected from the results of experiments without Pu and does not remain in this valence state, gradually transforming into Np(IV) (to ~30% within 5.5 h).…”

Section: Use Of Carbohydrazide For Stabilizing Desired Combinations Omentioning

confidence: 99%

“…Organic compounds show promise for this purpose. Their use allows the amount of salt-containing radioactive wastes to be sharply reduced [1]. Carbohydrazide (NH 2 NH) 2 CO can be one of such reagents.…”

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Reduction of Pu(IV) and Np(VI) with carbohydrazide in nitric acid solution

et al. 2012

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The reduction of Pu(IV) and Np(VI) with carbohydrazide (NH 2 NH) 2 CO in 1-6 M HNO 3 solutions was studied. The Pu(IV) reduction is described by a first-order rate equation with respect to Pu(IV). At [HNO 3 ] ≥ 3 M, the reaction becomes reversible. The rate constants of the forward and reverse reactions were determined, and their activation energies were estimated. Neptunium(VI) is reduced to Np(V) at a high rate, whereas the subsequent reduction of Np(V) to Np(IV) is considerably slower and is catalyzed by Fe and Tc ions. The possibility of using carbohydrazide for stabilizing desired combinations of Pu and Np valence states was examined.One of important lines of improving aqueous technology for reprocessing irradiated fuel, primarily highburn-up spent nuclear fuel, is search for new reagents, more convenient for performing redox operations involving Pu and Np ions. Organic compounds show promise for this purpose. Their use allows the amount of salt-containing radioactive wastes to be sharply reduced [1]. Carbohydrazide (NH 2 NH) 2 CO can be one of such reagents. Preliminary experiments showed that it rapidly reduces Pu(IV) and Np(VI) in nitric acid solutions at ambient temperature.In the literature, carbohydrazide was mainly examined as ligand for bi-and trivalent element ions [2][3][4][5]. Its reducing properties have been studied in considerably less detail. It is known that carbohydrazide reduces the Cu 2+ and Fe 3+ ions to Cu + and Fe 2+ , respectively. Both reactions occur at high rate and are accompanied by the evolution of gases: CO 2 and N 2 [6]. We found no data in the literature on interaction of actinide ions with carbohydrazide in nitric acid solutions. In this study we measured the rate of reduction of Pu(IV) and Np(VI) with carbohydrazide in HNO 3 solutions and examined the possibility of stabilizing Pu and Np in desirable valence state combinations using this reagent. Procedure.A temperature-controlled cell of a spectrophotometer was charged with the calculated amounts of stock solutions of HNO 3 and carbohydrazide and kept to attain the preset temperature. After that, a small aliquot of a Pu(IV) or Np(VI) solution was added, and the absorption spectra of the working solution were recorded at definite time intervals in the wavelength (λ) range 350-1100 nm. The concentration of the Pu and Np valence forms was calculated from the optical density (D) at λ = 475, 602, 980, and 710 nm, corresponding to the absorption maxima of the Pu 4+ , Pu 3+ , NpO 2 + , and Np 4+ ions, respectively.Chemicals and analysis. The Pu stock solution was prepared by dissolving PuO 2 in a boiling mixture of HNO 3 and HF. After the complete dissolution of PuO 2 , Al(NO 3 ) 3 was added to bind F -anions in a complex. The resulting solution was acidified with HNO 3 to a concentration of 7 M and purified by sorption on VP-1Ap anion exchanger. The desorbate was evaporated, and Pu was stabilized in the tetravalent state by adding H 2 O 2 . The solution thus prepared contained 440 g l -1 Pu and 6.6 M HNO 3 .

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Section: Use Of Carbohydrazide For Stabilizing Desired Combinations Omentioning

confidence: 99%

Section: Use Of Carbohydrazide For Stabilizing Desired Combinations Omentioning

confidence: 99%

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Reduction of Pu(IV) and Np(VI) with carbohydrazide in nitric acid solution

et al. 2012

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“…Besides the latter processes, an oxidation of the reduced forms of actinides by atmospheric oxygen must also be taken into account. As a result, SNF reprocessing media are extremely complex systems influenced by numerous factors [16].…”

Section: Introductionmentioning

confidence: 99%

Restoring important process information from complex optical spectra with MCR-ALS: Case study of actinide reduction in spent nuclear fuel reprocessing

Debus

Kirsanov

Ruckebusch

et al. 2015

Chemometrics and Intelligent Laboratory Systems

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“…One of the lines in improving aqueous technology for SNF reprocessing is search for new effective reagents for performing redox processes involving Pu and Np ions [1]. The results of our previous studies [2,3] show that carbohydrazide (NH 2 NH) 2 CO can be a candidate reagent for the Pu and Np reduction.…”

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Stripping of Pu and Tc from tributyl phosphate solutions with carbohydrazide

Alekseenko¹,

Marchenko²,

Dvoeglazov³

et al. 2012

Radiochemistry

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Stripping of Pu from 30% tributyl phosphate solutions with carbohydrazide was studied. The degree of the Pu stripping drastically decreases with an increase in acidity and increases with an increase in the carbohydrazide concentration and in temperature. The Pu(IV) reduction rate in the two-phase system is sufficiently high to perform the reductive stripping of Pu with carbohydrazides both in mixer-settlers and in centrifugal extractors. Stripping of Тс at high phase ratio (O/W = 30) with carbohydrazide, hydrazine, and U(IV) in a mixture with hydrazine was studied. At low acidity (<1 M HNO 3 ) and 30-35°C, carbohydrazide allows more than 80% stripping of Tc from 30% TBP solutions even at high volume ratio of the phases.One of the lines in improving aqueous technology for SNF reprocessing is search for new effective reagents for performing redox processes involving Pu and Np ions [1]. The results of our previous studies [2,3] show that carbohydrazide (NH 2 NH) 2 CO can be a candidate reagent for the Pu and Np reduction. Its advantages are high rate of the reaction with Pu(IV) and Np(VI) in aqueous solution, resistance to oxidation in HNO 3 solutions, and the absence of HN 3 among products of its reactions with HNO 3 and HNO 2 . Furthermore, thanks to a high rate of the reaction with HNO 2 , the use of carbohydrazide (CH) does not require introduction of any antinitrite agent (hydrazine) for stabilization of lower valence states of U, Pu, and Np.Another possible application of carbohydrazide is decontamination of U from Tc by the reduction of Tc(VII) to nonextractable Tc(IV) in the final step of the extraction reprocessing of SNF, because specifically 99 Tc (along with 106 Ru) is the nuclide determining the purity of the final uranium product.The goal of this study was to examine the possibility of using carbohydrazide in two-phase extraction systems with TBP for the Pu and Tc reduction and to perform laboratory trials of the reductive stripping of Pu under the conditions of the first extraction cycle and of the U decontamination from Tc in the step of extraction refining of U.The experimental procedure was as follows. A temperature-controlled separating funnel was charged with an aqueous nitric acid solution of carbohydrazide of known concentration, and an equal volume of a 30 vol % solution of TBP in n-dodecane, containing 0.9 to 1.1 g l -1 Pu(IV), was added. The contents were mechanically stirred for a definite time, after which the phases were separated by settling, and the Pu concentration in the organic phase was determined radiometrically, and that in the aqueous phase, spectrophotometrically. In each experiment, we also determined the concentration of H + ions in the aqueous phase by potentiometric titration. The Pu distribution ratio D and the degree of Pu stripping α were calculated by the formulas D = [Pu] org /[Pu] aq and α = (1 -[Pu] org /[Pu] org,init ) × 100%, where [Pu] org and [Pu] aq are the Pu concentrations in the organic and aqueous phases after the phase separation, and [Pu] org, init is the P...

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Use of redox reagents for stabilization of Pu and Np valence forms in aqueous reprocessing of spent nuclear fuel: Chemical and technological aspects

Cited by 35 publications

References 39 publications

Reduction of Pu(IV) and Np(VI) with carbohydrazide in nitric acid solution

Reduction of Pu(IV) and Np(VI) with carbohydrazide in nitric acid solution

Restoring important process information from complex optical spectra with MCR-ALS: Case study of actinide reduction in spent nuclear fuel reprocessing

Stripping of Pu and Tc from tributyl phosphate solutions with carbohydrazide

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