EP3365897B1 - Use of aldoximes comprising at least 5 five carbon atoms as anti-nitric agent in reductive plutonium back-extraction-operations - Google Patents

Description

TECHNICAL AREA

The invention relates to the field of the treatment of spent nuclear fuels.

More specifically, the invention relates to the use of aldoximes comprising at least five carbon atoms as anti-nitrous agents in reductive plutonium de-extraction operations.

The invention is applicable to all spent nuclear fuel treatment processes that include one or more plutonium reducing desuperation operations.

Such operations are particularly present in the PUREX process as it is implemented in modern spent nuclear fuel treatment plants (that is to say the UP3 and UP2-800 plants of La Hague in France and Rokkasho plant in Japan), firstly to carry out the U / Pu partitioning step of the first decontamination cycle of this process and, secondly, to complete the decontamination of plutonium into fission products in the process. plutonium purification cycle, conventionally called "plutonium second cycle", which follows this first cycle of decontamination.

They are also present in a number of processes derived from this PUREX process, such as, for example, that described in the international application PCT WO 2006/072729 [1], known as the COEX process or the one described in the international application PCT WO 2011/000844 [2].

STATE OF THE PRIOR ART

The plutonium reducing desextraction operations, which are carried out in the above-mentioned processes for the treatment of spent nuclear fuel, consist of passing the plutonium from an organic phase (or solvent phase), in which it is at the stage of oxidation (IV), in an aqueous phase by reducing it to the oxidation state (III), a state in which its affinity for the organic phase is very low.

The reduction of plutonium (IV) to plutonium (III) is induced by a reducing agent which is added to the aqueous phase used for the desextraction and stabilized by an anti-nitrous agent.

In the case, for example, of the first decontamination cycle of the PUREX process as it is implemented in modern spent fuel treatment plants (which will be called more simply "PUREX process" in the following), the Reducing agent used to extract the plutonium during the partition stage U / Pu is uranium (IV) (or uranous nitrate), while the anti-nitrous agent is hydrazinium nitrate, also called hydrazine.

• la réduction du plutonium(IV) en plutonium(III) par l'uranium(IV) (réaction fonctionnelle) :
  
          U⁴⁺ + 2Pu⁴⁺ + 2H₂O → UO₂ ²⁺ + 2Pu³⁺ + 4H⁺
  
  
• la réoxydation du plutonium(III) en plutonium(IV) (réaction parasite) :
  
          Pu³⁺ + HNO₂ + 1,5H⁺ + 0,5NO₃ ^- → Pu⁴⁺ + 0,5H₂O +1,5HNO₂
  
  
• la destruction de l'acide nitreux en acide azothydrique par l'hydrazine (réaction utile) :
  
          N₂H₅NO₃ + HNO₂ → N₃H + HNO₃ + 2H₂O.
  
  

The main chemical reactions to consider are:

• the reduction of plutonium (IV) in plutonium (III) by uranium (IV) (functional reaction):
  
  U ⁴⁺ + 2Pu ⁴⁺ + 2H ₂ O → UO ₂ ²⁺ + 2Pu ³⁺ + 4H ⁺
  
  
• the reoxidation of plutonium (III) into plutonium (IV) (parasitic reaction):
  
  Pu ³⁺ + HNO ₂ + 1,5H ⁺ + 0,5NO ₃ ^- → Pu ⁴⁺ + 0,5H ₂ O + 1,5HNO ₂
  
  
• destruction of nitrous acid to azohydric acid by hydrazine (useful reaction):
  
  N ₂ H ₅ NO ₃ + HNO ₂ → N ₃ H + HNO ₃ + 2H ₂ O.
  
  

The first two reactions take place in the aqueous and organic phases whereas the reaction of destruction of nitrous acid by hydrazine takes place only in the aqueous phase because of the inextractability of hydrazine by the organic phase. , the latter being composed of 30% (v / v) tri-n-butyl phosphate (or TBP) in hydrogenated tetrapropylene (or TPH).

The presence of plutonium (III) in the organic phase, even in small quantities, catalyzes the oxidation of uranium (IV) through the first two reactions and thus generates nitrous acid.

It has been observed in experimental studies carried out in centrifugal extractors of the laboratory that, even with short residence times in an extractor (of the order of a few seconds), the consumption by oxidation of uranium (IV) is very important. This oxidation of uranium (IV) develops mainly in the organic phase, hydrazine being present only in aqueous phase. Also, the operating schemes of the plutonium reductive desextraction operations provide for a large excess of reducing agent.

The azohydric acid formed by the destruction reaction of nitrous acid with hydrazine reacts in turn with nitrous acid according to the reaction:

HN ₃ + HNO ₂ → N ₂ + N ₂ O + H ₂ O.

The kinetics of this reaction, however, is much slower than the destruction reaction of nitrous acid with hydrazine so that azohydric acid is found in the aqueous and organic phases effluents of the partition stage U / Pu.

Thus, the fact that the hydrazine is not extractable by the organic phase and therefore acts only in aqueous phase leads to a high consumption of reagents and the production of chemical species that are binding for the industrial exploitation of the process .

To solve this problem, it has been proposed in the international application PCT WO 2008/148863 [3], to use a biphasic anti-nitrous system associating butanal oxime, also called butyraldehyde oxime or butyraldoxime, with hydrazine, butanal oxime making it possible indeed to stabilize the organic phase while hydrazine stabilizes the aqueous phase.

• de l'extraction relativement faible de la butanal oxime par la phase organique, ce qui oblige à introduire cette oxime en grande quantité dans l'extracteur dans lequel se déroule la désextraction réductrice du plutonium si l'on veut obtenir une concentration efficace de butanal oxime en phase organique ; en particulier, dans l'étape de partition U/Pu, l'extraction de la butanal oxime par la phase organique est fortement diminuée par la saturation de cette phase en actinides, ce qui rend in fine l'utilisation de cette oxime peu adaptée à la réalisation de cette étape de partition ;
• du maintien de l'utilisation d'hydrazine en phase aqueuse ; en effet, en dépit du fait que l'hydrazine soit un agent anti-nitreux des plus efficaces en phase aqueuse, son utilisation est contraignante, non seulement en raison des problèmes précédemment évoqués, liés à la formation d'acide azothydrique, mais également en raison de sa toxicité ; en effet, l'hydrazine fait partie de la liste des substances CMR, c'est-à-dire les substances qui sont considérées par le règlement (CE) 1907/2006 sur l'enregistrement, l'évaluation, l'autorisation et les restrictions des produits chimiques (règlement REACH) comme potentiellement ou de manière avérée cancérigènes, mutagènes et/ou toxiques pour la reproduction, et est susceptible d'être inscrite à plus ou moins long terme à l'annexe XIV de ce règlement, auquel cas sa mise sur le marché et son utilisation industrielle seront interdites sauf dérogation spécifique de l'Agence européenne des produits chimique (ECHA).

If the use of butanal oxime, in combination with hydrazine, has a number of advantages, in particular in that it makes it possible to reduce the quantities of uranous nitrate and of hydrazine necessary for the realization of a reductive extraction of plutonium and thus lessen the drawbacks related to the non-extraction of hydrazine in the organic phase, but it is not totally satisfactory from made :

• the relatively low extraction of butanal oxime by the organic phase, which makes it necessary to introduce this oxime in large quantities into the extractor in which the reductive extraction of plutonium takes place if an effective concentration of butanal oxime is to be obtained in the organic phase; in particular, in the U / Pu partitioning step, the extraction of butanal oxime by the organic phase is greatly reduced by the saturation of this phase with actinides, which ultimately makes the use of this oxime unsuitable for the realization of this step of partition;
• maintaining the use of hydrazine in the aqueous phase; indeed, despite the fact that hydrazine is a most effective anti-nitrous agent in the aqueous phase, its use is restrictive, not only because of the problems mentioned above, related to the formation of azohydric acid, but also in because of its toxicity; in fact, hydrazine is part of the list of CMR substances, ie the substances that are considered by Regulation (EC) 1907/2006 on the registration, evaluation, authorization and chemical substances (REACH Regulation) as potentially or in a known way carcinogenic, mutagenic and / or toxic for reproduction, and is likely to be listed in the more or less long term in Annex XIV of this Regulation, in which case its placing on the market and its industrial use will be prohibited unless specifically granted by the European Chemicals Agency (ECHA).

In addition, a reaction of butanal oxime with hydrazine, leading to the formation of a hydrazone, was observed. However, this reaction reduces the performance of butanal oxime and leads to overconsumption of these two reagents.

In view of the foregoing, the inventors have therefore set themselves the goal of finding compounds having a high anti-nitrous power but the use of which is free from the disadvantages presented by the use of hydrazine such as currently implemented in the PUREX process or by the use of a biphasic butanal oxime / hydrazine system as proposed in reference [3].

More specifically, they have set themselves the goal that these compounds are more extractable by an organic phase, in particular of the type used in the PUREX process, than is the butanal oxime (under the same conditions of temperature and humidity). pressure), including when this organic phase is saturated with actinides, so as to be able (1) to reduce the quantities of these compounds necessary for the realization of a reductive desextraction of the plutonium and (2) to use them as well to extract the plutonium in the U / Pu partitioning step of the first decontamination cycle of the PUREX process only to detoxify the plutonium in the second plutonium cycle of this process.

They have also set a goal that these compounds can completely overcome the use of hydrazine.

STATEMENT OF THE INVENTION

These and other objects are achieved by the invention which proposes to use at least one aldoxime comprising at least 5 carbon atoms, that is to say an oxime of formula R-CH = N-OH in which R represents a hydrocarbon chain comprising at least 4 carbon atoms, as anti-nitrous agent in a reductive plutonium de-extraction operation.

Preferably, the aldoxime corresponds to the above formula in which R comprises at most 12 carbon atoms and, advantageously, at most 8 carbon atoms.

More preferably, the aldoxime corresponds to the above formula wherein R represents a linear alkyl chain comprising from 4 to 8 carbon atoms.

Such aldoximes are pentanal oxime, also called valeraldehyde oxime or valeraldoxime, of formula n -C ₄ H ₉ -CH = N-OH, hexanal oxime of formula n -C ₅ H ₁₁ -CH = N-OH, the heptanal oxime of formula n -C ₆ H ₁₃ -CH = N-OH, the octanal oxime of formula n- C ₇ H ₁₅ -CH = N-OH and the nonanal oxime of formula n -C ₈ H ₁₇ - CH = N-OH.

Among these aldoximes, pentanal oxime and hexanal oxime are particularly preferred.

• la mise en contact d'une phase organique, non miscible à l'eau, comprenant un agent extractant et le plutonium au degré d'oxydation IV dans un diluant organique, avec une phase aqueuse comprenant un agent réducteur capable de réduire le plutonium(IV) en plutonium(III) et de l'acide nitrique, l'aldoxime étant présente soit dans la phase organique soit dans la phase aqueuse selon sa solubilité dans l'eau ; puis
• la séparation des phases organique et aqueuse ainsi mises en contact.

According to the invention, the process of reducing the extraction of plutonium preferably comprises:

• contacting an organic phase, immiscible with water, comprising an extractant and the plutonium at the oxidation state IV in an organic diluent, with an aqueous phase comprising a reducing agent capable of reducing the plutonium (IV ) in plutonium (III) and nitric acid, the aldoxime being present either in the organic phase or in the aqueous phase according to its solubility in water; then
• the separation of the organic and aqueous phases thus brought into contact.

Thus, pentanal oxime, which is partially soluble in water and partially soluble in organic diluents that may be used in plutonium-reducing reductive extraction operations (under the conditions of temperature and pressure conventionally used in these operations), may be added to the aqueous phase as well as to the organic phase while the aldoximes containing 6 or more carbon atoms, which are insoluble or almost insoluble in water (under the aforementioned conditions), are added to the organic phase.

According to the invention, the reducing agent present in the aqueous phase is preferably chosen from uranium (IV), hydroxylammonium nitrate, also called hydroxylamine nitrate, alkylated hydroxylamine derivatives, Ferrous sulfamate and sulfamic acid.

Among these reducing agents, uranium (IV) and hydroxylammonium nitrate are particularly preferred, which are the two agents which are used to reduce plutonium (IV) to plutonium (III) in the PUREX process, the first in the U / Pu partition stage of the first decontamination cycle, the second in the second plutonium cycle.

On the other hand, the extracting agent is preferably a tri-n-alkyl phosphate and, more preferably, TBP while the organic diluent is preferably a linear or branched dodecane such as n-dodecane or TPH, an isoparaffinic solvent such as Isane IP185, Isane IP165 or Isopar L, or kerosene, in which case the extracting agent is preferably present at 30% (v / v) in this organic diluent.

In all cases, aldoxime is used at a concentration ranging preferably from 0.01 mol / L to 3 mol / L and, more preferably, from 0.05 mol / L to 0.5 mol / L of organic or aqueous phase, while the reducing agent is used, preferably, at a concentration ranging from 0.2 mol / L to 0.6 mol / L and more preferably 0.2 mol / L at 0.4 mol / L of aqueous phase.

As for the nitric acid, it is advantageously present in the aqueous phase at a concentration ranging from 0.05 mol / l to 2 mol / l.

According to the invention, aldoxime can be used as the sole anti-nitrous agent in the plutonium reductive desextraction operation if it is distributed in a balanced manner between the organic phase and the aqueous phase when they are brought into contact with each other. with each other. However, when this is not the case because aldoxime is highly extractable by the organic phase (under the conditions of temperature and pressure conventionally used in plutonium reductive de-extraction operations), which will typically occur for aldoximes having 6 or more carbon atoms such as hexanal oxime, heptanal oxime or octanal oxime -, then this aldoxime is advantageously used in combination with a second anti-nitrous agent which is itself an oxime no extractable by this organic phase (under the same conditions of temperature and pressure).

In which case, this non-extractable oxime, which is present in the aqueous phase, is preferably formaldoxime, also called formaldehyde oxime, of formula CH ₂ = N-OH, or acetaldoxime, also called acetaldehyde oxime , of formula CH ₃ -CH = N-OH, and is advantageously used at a concentration ranging from 0.01 mol / l to 1 mol / l and, more preferably, from 0.05 mol / l to 0.2 mol / L of aqueous phase.

According to a particularly preferred embodiment of the invention, the plutonium reducing desextraction operation is preferably one of the PUREX process plutonium or COEX process extraction operations.

The invention has many advantages. Indeed, it offers a range of anti-nitrous agents which are capable, for some when used alone and for others when used in combination with an oxime not extractable by an organic phase, to block very well. effectively the reoxidation of plutonium (III) to plutonium (IV) both in an organic phase and in an aqueous phase.

As a result, in addition to the fact that the invention makes it possible to carry out reductive plutonium de-extraction operations without the use of hydrazine, whether this is an operation such as that which is carried out in the U / Pu partition of the PUREX process or of an operation such as that implemented in the second plutonium cycle of the same process, it also makes it possible to reduce very strongly the quantities of reducing agent and anti-nitride agent required. performing these operations with respect to the quantities required when the anti-nitrous agent is hydrazine.

It therefore makes it possible to envisage a reduction in the number of points necessary for the introduction of these anti-nitrous agents into the apparatus devolved to the plutonium reducing desextraction operations and thus a simplification of these apparatuses.

In addition, the plutonium de-extraction being more efficient and thus leading to obtaining, at the end of the extraction operation, an aqueous phase which is more concentrated in plutonium than that obtained by using hydrazine as an anti-oxidation agent. However, the invention also makes it possible to envisage a reduction in the dimensioning of the apparatus currently used to carry out reductive plutonium removal operations.

Other features and other advantages of the invention will appear better on reading the examples which follow.

Of course, these examples are given only as illustrations of the subject of the invention and do not constitute in any way a limitation of this object.

BRIEF DESCRIPTION OF THE FIGURES

• The figure 1 presents the distribution coefficients of pentanal oxime (symbol I) and hexanal oxime (symbol I) between organic phases comprising TBP in n-dodecane and aqueous phases comprising different concentrations of nitric acid; for comparison, are also shown in this figure the distribution coefficients as obtained under the same conditions for butanal oxime (symbol ▲).
• The Figures 2A and 2B present the distribution coefficients of pentanal oxime (symbol I) and hexanal oxime (symbol I) between organic phases and aqueous phases simulating, in terms of uranium concentration (VI) and concentration of nitric acid the organic phases and the aqueous phases which are obtained during the U / Pu partitioning step of the PUREX process.
• The figure 3 illustrates the kinetics of destruction of nitrous acid by pentanal oxime (curve A) in a nitric aqueous phase; for comparison, are also shown in this figure the kinetics of destruction of nitrous acid by butanal oxime (curve B) and acetaldoxime (curve C) as obtained under the same conditions.
• The figure 4 illustrates the kinetics of destruction of nitrous acid by pentanal oxime (curve A) and hexanal oxime (curve B) in organic phases comprising TBP in n-dodecane; for comparison, is also shown in this figure the kinetics of destruction of nitrous acid by butanal oxime (curve C) as obtained under the same conditions.
• The figure 5 illustrates the oxidation kinetics of uranium (IV) obtained in the presence of pentanal oxime (curve A) and hexanal oxime (curve B) in organic phases comprising TBP in n-dodecane, after contacting these organic phases with a nitric aqueous phase and then separation of these phases; for comparison, are also represented in this figure oxidation kinetics of uranium (IV) as obtained, under the same conditions, in the presence of butanal oxime (curve C) and in the absence of any oxime (curve D).
• The figure 6 illustrates the kinetics of oxidation of uranium (IV) obtained in the presence of pentanal oxime (curve A) in a nitric aqueous phase; for comparison, are also shown in this figure the oxidation kinetics of uranium (IV) as obtained, under the same conditions, in the presence of butanal oxime (curve B), acetaldoxime (curve C) and hydrazine (curve D).
• The figure 7 illustrates the kinetics of oxidation of uranium (IV) present in an organic phase (TBP / TPH) resulting from a reductive plutonium desextraction test in which hexanal oxime was used as an anti-nitrous agent.
• The figure 8 illustrates the kinetics of oxidation of uranium (IV) present in an organic phase (TBP / TPH) resulting from a reductive plutonium desextraction test in which hexanal oxime was used as an anti-nitrous agent and in which technetium was desextracted together with the plutonium.
• The figure 9 illustrates the kinetics of oxidation of uranium (IV) in an organic phase (TBP / TPH) resulting from a reductive plutonium desextraction test in which pentanal oxime was used as an anti-nitrous agent.
• The figure 10 illustrates the oxidation kinetics of uranium (IV) in the presence of acetaldoxime in aqueous nitric phases comprising 100 mg / L (symbol ■) or 200 mg / L (symbol ×) of technetium; for comparison, are also represented in this figure oxidation kinetics of uranium (IV) as obtained, under the same conditions, in the presence of hydrazine and 100 mg / L (symbol ▲) or 200 mg / L (symbol ●) of technetium.
• The figure 11 illustrates a scheme for treating a spent nuclear fuel dissolution liquor comprising a U / Pu partitioning step in which a hexanal oxime / acetaldoxime combination is used as an anti-nitrous system; in this figure, the rectangles referenced 1 to 7 represent multi-stage extractors such as those conventionally used in the treatment of spent nuclear fuels (mixer-settlers, pulsed columns, centrifugal extractors); Moreover, the organic phases entering and leaving the extractors are symbolized by solid lines, while the aqueous phases entering and leaving these extractors are symbolized by dashed lines.
• The figure 12 illustrates the profile of the concentrations of uranium (IV) in the aqueous phases circulating in the extractors 5 and 6 of the diagram illustrated on the figure 11 as obtained by calculations (curve A); for comparison, are also the profile of the concentrations of uranium (IV) that would be obtained if hexanal oxime and acetaldoxime were replaced in this scheme by hydrazine (curve B) and the profile of uranium concentrations (IV ) that would be obtained if the reoxidation reactions of plutonium (III) were completely neutralized (curve C).
• The figure 13 illustrates the profiles of the concentrations of plutonium in the aqueous phases circulating in the extractors 5 and 6 of the diagram illustrated on the figure 11 , as obtained experimentally (symbol ×) and by calculations (curve -).
• The figure 14 illustrates the concentration profiles of uranium (IV), uranium (VI) and total uranium in the aqueous phases circulating in extractors 5 and 6 of the diagram shown in figure 11 as obtained experimentally and by calculations; in this figure, the symbols ×, ◆ and ■ respectively correspond to the profiles of the concentrations of uranium (VI), uranium (IV) and total uranium obtained experimentally, whereas the curves A, B and C correspond respectively to the profiles of the concentrations of uranium (VI), uranium (IV) and total uranium obtained by calculations.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS EXAMPLE 1 Properties of pentanal oxime and hexanal oxime 1.1 - Distribution coefficients

• une première série visant à déterminer ces coefficients de distribution entre des phases organiques comprenant 30% (v/v) de TBP dans le n-dodécane et des phases aqueuses comprenant de 0,2 mol/L à 2 mol/L d'acide nitrique ; et
• une deuxième série visant à déterminer ces coefficients de distribution entre des phases organiques et des phases aqueuses simulant, en termes de concentration d'uranium(VI) et de concentration d'acide nitrique, les phases organiques et les phases aqueuses qui sont obtenues au cours de l'étape de partition U/Pu du procédé PUREX, cette mise en œuvre étant réalisée dans une batterie à 8 étages de mélangeurs-décanteurs, notés BX1 à BX8.

The distribution coefficients, denoted D, of pentanal oxime and hexanal oxime were determined by two series of tests, namely:

• a first series aimed at determining these distribution coefficients between organic phases comprising 30% (v / v) of TBP in n-dodecane and aqueous phases comprising from 0.2 mol / L to 2 mol / L of nitric acid ; and
• a second series aimed at determining these distribution coefficients between organic phases and aqueous phases simulating, in terms of uranium concentration (VI) and concentration of nitric acid, the organic phases and the aqueous phases which are obtained during of the U / Pu partition stage of the PUREX process, this implementation being carried out in an 8-stage mixer-settler battery, denoted BX1 to BX8.

To do this, in both sets of tests, each organic phase was brought into contact, volume to volume, for 15 minutes, at room temperature (20-25 ° C.) and with stirring, with a nitric aqueous phase. Pentanal oxime was added to the aqueous phase while hexanal oxime was added to the organic phase, each at a concentration of 0.1 mol / L of phase.

The organic and aqueous phases thus brought into contact were separated from each other by centrifugation and the concentrations of aldoxime in these phases were measured by high performance liquid chromatography (HPLC) for the aqueous phases and chromatography. gas phase (GC) for the organic phases.

The distribution coefficients obtained in the first series of tests are presented in Table 1 below. They are also featured on the figure 1 in which the values indicated in this table have been transposed and in which the distribution coefficients of the pentanal oxime are represented by the symbol ■ while the distribution coefficients of the hexanal oxime are represented by the symbol ●. For comparison, are also illustrated on the figure 1 the distribution coefficients obtained under the same conditions for butanal oxime (▲). Table 1 [HNO ₃ ] _aq. (Mol / L) D Pentanal oxime Hexanal oxime 0.2 20.7 140.7 0.5 16.0 93.0 0.75 11.0 62.5 1 8.2 34.1 2 1.8 7.7

The distribution coefficients obtained in the second series of tests are presented in Table 2 below. They are also featured on Figures 2A and 2B in which the values of the distribution coefficients (in ordinate) and of the acidity of the aqueous phases (in abscissa) have been transposed and in which the distribution coefficients of the pentanal oxime correspond to the symbol ■ whereas the distribution coefficients of the hexanal oxime correspond to the symbol ●. The ordinates are at a decimal scale on the Figure 2A and on a logarithmic scale on the Figure 2B . Table 2 testing Pentanal oxime Hexanal oxime [HNO ₃ ] _aq. (Mol / L) [U] _aq. (G / L) [U] _org. (G / L) D [HNO ₃ ] _aq. (Mol / L) [U] _aq. (G / L) [U] _org. (G / L) D BX1 2.05 21.4 82.6 0.90 2.06 22,19 80.29 4.12 BX2 1.65 26 81.5 1.75 1.76 27.78 77.66 5.94 BX3 1.39 33,15 80.1 2.36 1.52 32.12 79.93 7.06 BX4 1.09 38.3 78.6 3.26 1.14 39.52 77.8 13.42 BX5 0.89 44.8 78.9 4.10 0.91 45.81 76.3 14.83 BX6 0.67 54.1 76.7 5.64 0.66 55.93 75.58 26.33 BX7 0.5 65.4 75.9 6.99 0.43 71.68 74.4 34.38 BX8 0.39 73 70.1 10.21 0.34 78.35 70.55 50.49

As shown in Table 1 and figure 1 pentanal oxime and hexanal oxime have much higher distribution coefficients than butanal oxime, which means that they are much more extractable in the organic phase than the latter.

When the aqueous phase is loaded with actinides (Table 2 and Figures 2A and 2B ), the distribution coefficients of pentanal oxime and hexanal oxime are decreased compared to what they are in the absence of actinides; however, they remain high enough that pentanal oxime and hexanal oxime are still significantly extracted. Under the same conditions, the distribution coefficients of butanal oxime are less than 1.

• pour la pentanal oxime : une distribution équilibrée entre phase organique et phase aqueuse, d'où la possibilité de développer des schémas de désextraction réductrice du plutonium dans lesquels la pentanal oxime serait utilisée seule pour stabiliser à la fois la phase organique et la phase aqueuse ; tandis que
• pour l'hexanal oxime : une extraction quasi quantitative en phase organique, d'où la possibilité de développer des schémas de désextraction réductrice du plutonium dans lesquels l'hexanal oxime serait utilisée, en très faible quantité, pour stabiliser la phase organique, la phase aqueuse pouvant alors être stabilisée par une oxime hydrophile comme l'acétaldoxime ; et
• pour ces deux aldoximes : la possibilité de les utiliser dans une étape de partition U/Pu.

The distribution coefficients of pentanal oxime and hexanal oxime allow:

• for pentanal oxime: a balanced distribution between organic phase and aqueous phase, hence the possibility of developing reductive plutonium desextraction schemes in which pentanal oxime would be used alone to stabilize both the organic phase and the aqueous phase; while
• for hexanal oxime: a quasi-quantitative extraction in the organic phase, hence the possibility of developing reductive plutonium desextraction schemes in which hexanal oxime would be used, in very small quantities, to stabilize the organic phase, the phase aqueous can then be stabilized by a hydrophilic oxime such as acetaldoxime; and
• for these two aldoximes: the possibility of using them in a partition stage U / Pu.

1.2 - Anti-nitrous action

• une première série visant à établir la cinétique de destruction de l'acide nitreux par la pentanal oxime et, à titre de comparaison, la cinétique de destruction de l'acide nitreux par la butanal oxime dans des phases aqueuses comprenant 0,1 mol/L d'acide nitrique ; et
• une deuxième série visant à établir les cinétiques de destruction de l'acide nitreux par la pentanal oxime et par l'hexanal oxime et, à titre de comparaison, la cinétique de destruction de l'acide nitreux par la butanal oxime dans des phases organiques comprenant 30% (v/v) de TBP dans du n-dodécane.

The ability of pentanal oxime and hexanal oxime to destroy nitrous acid (HNO ₂ ) was assessed by two series of tests, namely:

• a first series aimed at establishing the kinetics of destruction of nitrous acid by pentanal oxime and, for comparison, the kinetics of destruction of nitrous acid by butanal oxime in aqueous phases comprising 0.1 mol / L nitric acid; and
• a second series aimed at establishing the kinetics of destruction of nitrous acid by pentanal oxime and hexanal oxime and, for comparison, the kinetics of destruction of nitrous acid by butanal oxime in organic phases comprising 30% (v / v) TBP in n-dodecane.

In the first series of tests, the initial concentrations of nitrous acid and pentanal oxime or butanal oxime in the nitric aqueous phases were 0.005 mol / L and 0.025 mol / L, respectively. The evolution over time of the concentration of nitrous acid in these aqueous phases was followed spectrophotometrically (continuous measurement of the HNO ₂ peak at λ = 370 nm).

In the second series of tests, a first batch of organic phases, previously equilibrated with 1M nitric acid, was first contacted, volume-to-volume, for 10 minutes at room temperature (20- 25 ° C) and with stirring, with an aqueous phase comprising 1 mol / L of nitric acid and 0.002 mol / L of nitrous acid, and then separated from this aqueous phase by centrifugation. Nitrous acid is extracted almost quantitatively in the organic phases.

Then a second batch of organic phases, previously equilibrated with 1 M nitric acid and to which were added pentanal oxime, hexanal oxime or butanal oxime at a concentration of 0.15 mol / L of phase organic, was brought into contact, volume by volume, for 10 minutes, at ambient temperature (20-25 ° C.) and with stirring, with an aqueous phase comprising 1 mol / L of nitric acid, and then separated from this aqueous phase. by centrifugation. The oximes are partitioned between the organic phases and the aqueous phase.

Rapid mixing is then carried out between 1 mL of the organic phases from the first batch (and thus comprising nitrous acid) and 8 mL of the organic phases from the second batch. The evolution of the concentration of nitrous acid in these mixtures was followed spectrophotometrically (λ = 370 nm).

The results of these tests are illustrated on the figures 3 and 4 , in the form of curves expressing the percentage of residual nitrous acid as a function of time (in seconds on the figure 3 and in minutes on the figure 4 ).

On the figure 3 , which relates to the first series of tests, curve A corresponds to the results obtained for pentanal oxime while curve B corresponds to the results obtained for butanal oxime. This figure also shows the kinetics of destruction of nitrous acid by acetaldoxime (curve C), this kinetics having been determined by simulation from the kinetic constant measured experimentally.

On the figure 4 , which refers to the second series of tests, curve A corresponds to the results obtained for pentanal oxime; curve B corresponds to the results obtained for hexanal oxime while curve C corresponds to the results obtained for butanal oxime.

• dans un système monophasique aqueux, la pentanal oxime, bien que comprenant un nombre d'atomes de carbone supérieur à celui que présentent la butanal oxime et l'acétaldoxime, présente une action anti-nitreuse équivalente à celle de la butanal oxime et de l'acétaldoxime (figure 3) ; tandis que
• dans un système monophasique organique dans lequel la phase organique contenant de la pentanal oxime, de l'hexanal oxime ou de la butanal oxime a été préalablement mise en contact avec une phase aqueuse (ce qui a conduit à un partage de ces oximes entre phase organique et phase aqueuse, d'où une diminution de leur concentration en phase organique), on observe que, pour une même concentration d'oxime initialement introduite en phase organique, la destruction de l'acide nitreux en phase organique est nettement accélérée en présence de pentanal oxime ou d'hexanal oxime par rapport à ce qu'elle est en présence de butanal oxime (figure 4).

These figures show that:

• in a single-phase aqueous system, pentanal oxime, although containing a number of carbon atoms greater than that of butanal oxime and acetaldoxime, has an anti-nitrous action equivalent to that of butanal oxime and acetaldoxime ( figure 3 ); while
• in an organic monophasic system in which the organic phase containing pentanal oxime, hexanal oxime or butanal oxime has been previously brought into contact with an aqueous phase (which has led to a sharing of these oximes between organic phase and an aqueous phase, hence a decrease in their concentration in the organic phase), it is observed that, for the same concentration of oxime initially introduced into the organic phase, the destruction of the nitrous acid in the organic phase is clearly accelerated in the presence of pentanal oxime or hexanal oxime compared to what it is in the presence of butanal oxime ( figure 4 ).

EXAMPLE 2 Stabilization of Actinides by Pentanal Oxime and Hexanal Oxime

• une première série visant à établir la cinétique d'oxydation de l'uranium(IV) en présence de pentanal oxime, d'hexanal oxime et, à titre de comparaison, de butanal oxime ainsi qu'en l'absence de toute oxime, dans des phases organiques comprenant 30% (v/v) de TBP dans du n-dodécane, après mise en contact de ces phases organiques avec des phases aqueuses comprenant 1,8 mol/L d'acide nitrique puis séparation de ces phases ; et
• une deuxième série visant à établir la cinétique d'oxydation de l'uranium(IV) en présence de pentanal oxime et, à titre de comparaison, de butanal oxime, d'acétaldoxime et d'hydrazine, dans des phases aqueuses comprenant 1,3 mol/L d'acide nitrique.

The ability of pentanal oxime and hexanal oxime to stabilize actinides in aqueous or organic phase was assessed by two series of tests, namely:

• a first series aimed at establishing the oxidation kinetics of uranium (IV) in the presence of pentanal oxime, hexanal oxime and, for comparison, butanal oxime and in the absence of any oxime, in organic phases comprising 30% (v / v) of TBP in n-dodecane, after bringing these organic phases into contact with aqueous phases comprising 1.8 mol / L of nitric acid and then separating these phases; and
• a second series aimed at establishing the oxidation kinetics of uranium (IV) in the presence of pentanal oxime and, for comparison, butanal oxime, acetaldoxime and hydrazine, in aqueous phases comprising 1.3 mol / L nitric acid.

In the first series of tests, each organic phase, previously equilibrated with 1.8 M nitric acid and in which was introduced, where appropriate, an oxime at a concentration of 0.1 mol / l was brought into contact, for 10 minutes, at room temperature (20-25 ° C.) and with stirring, with a nitric aqueous phase comprising 6 g / l of uranium (IV), in a volume ratio O / A of 2. Then the organic and aqueous phases thus brought into contact were separated from each other by centrifugation and the evolution of the concentrations of uranium (IV) in the organic phases was monitored spectrophotometrically (λ = 653 nm) at time intervals over a period of 200 hours.

In the second series of tests, the initial concentrations of uranium (IV) and the anti-nitrous agent (oxime or hydrazine) in the nitric aqueous phases were 66 g / L and 0.2 mol / L. The evolution over time of uranium (IV) concentrations in these aqueous phases was followed spectrophotometrically (λ = 653 nm) at time intervals over a period of 300 days.

The results of these tests are illustrated on the figures 5 and 6 in the form of curves expressing the percentage of uranium (IV) residual as a function of time (in hours on the figure 5 and in days on the figure 6 ).

On the figure 5 , which refers to the first series of tests, curve A corresponds to the results obtained for pentanal oxime; curve B corresponds to the results obtained for hexanal oxime; curve C corresponds to the results obtained for butanal oxime whereas curve D corresponds to the results obtained in the absence of oxime.

On the figure 6 , which refers to the second series of tests, curve A corresponds to the results obtained for pentanal oxime; curve B corresponds to the results obtained for butanal oxime; curve C corresponds to the results obtained for acetaldoxime whereas curve D corresponds to the results obtained for hydrazine.

As shown in figure 5 uranium (IV) is perfectly stable in the organic phase for at least 15 hours in the presence of an oxime while its oxidation is complete in less than 8 hours in the absence of any oxime. In addition, the ability of pentanal oxime and hexanal oxime to stabilize uranium (IV) in the organic phase is greater than that of butanal oxime since less than 10% of uranium (IV) are oxidized in 100 hours in the presence of pentanal oxime and hexanal oxime, which is not the case in the presence of butanal oxime.

In aqueous phase, the ability of pentanal oxime to stabilize uranium (IV) is also higher than that of butanal oxime. However, it is less than that of acetaldoxime and that of hydrazine which are comparable to each other ( figure 6 ).

All these durations, in days, are nevertheless considerably greater than the durations of presence of the organic and aqueous phases in the industrial operations of plutonium desextraction.

These results show the possibility of stabilizing nitric aqueous phases highly concentrated in uranium (IV) either with pentanal oxime in the case of a single oxime scheme or with acetaldoxime in the case of a two oximes scheme, for example with hexanal oxime in the organic phase, and to overcome the use of hydrazine.

EXAMPLE 3 Anti-Nitrous Power of Pentanal Oxime and Hexanal Oxime Under Chemical Conditions Representative of those of a Reductive Plasmonium Destracting Operation

• une réduction par l'uranium(IV) du plutonium(IV) en plutonium(III) et une réoxydation par l'acide nitreux du plutonium(III) en plutonium(IV) ;
• une destruction de l'acide nitreux par l'une des oximes précitées; et
• une distribution des espèces d'intérêt entre phase aqueuse et phase organique.

The anti-nitrous potency of pentanal oxime and hexanal oxime was evaluated in a series of tests, hereinafter referred to as BX1 to BX10, representative of the chemical conditions in which a plutonium reducing des-extraction operation is carried out. in the PUREX process, involving:

• a reduction by plutonium (IV) of uranium (IV) in plutonium (III) and a reoxidation by nitrous acid of plutonium (III) into plutonium (IV);
• a destruction of nitrous acid by one of the above oxime; and
• a distribution of the species of interest between aqueous phase and organic phase.

• comme phases aqueuses : des solutions à 1 mol/L ou 2 mol/L d'acide nitrique, comprenant de l'uranium(VI), de l'uranium(IV) (en tant qu'agent réducteur du plutonium(IV)) et, éventuellement, de l'hydrazine et du technétium, aux concentrations indiquées dans les tableaux 3 et 4 ci-après ; et
• comme phases organiques : des solutions de TBP à 30% (v/v) dans du TPH, comprenant une oxime, de l'uranium(VI) et du plutonium(IV) aux concentrations indiquées dans les tableaux 3 et 4 ci-après.

To do this, have been used:

• as aqueous phases: solutions of 1 mol / L or 2 mol / L of nitric acid, including uranium (VI), uranium (IV) (as reducing agent for plutonium (IV)) and, optionally, hydrazine and technetium, at the concentrations indicated in Tables 3 and 4 below; and
• as organic phases: TBP solutions at 30% (v / v) in TPH, comprising an oxime, uranium (VI) and plutonium (IV) at the concentrations indicated in Tables 3 and 4 below.

Oximes were introduced into the organic phases in solid form (the quantity of oxime introduced being controlled by weighing).

The organic phases and the aqueous phases were brought into contact for 15 minutes (except in the case of the BX3 test for which the contact time was only 5 minutes), at room temperature (20-25 ° C. ) and with stirring, in a volume ratio O / A of 2, then these phases were separated from each other.

After this separation, the concentrations of uranium (VI), uranium (IV) and plutonium (III) in the aqueous phases were measured by UV-visible spectrophotometry and total plutonium by alpha spectrometry. The concentrations of uranium (VI) and uranium (IV) in the organic phases were measured by UV-visible spectrophotometry and that of the total plutonium by alpha spectrometry.

From the results of these measurements were determined for each test, the ratio between the amounts of uranium (IV) and plutonium used back-extracted, denoted U (IV) _cons ./Pu _dice. And the factor plutonium separation, noted FD _Pu .

The results of these tests are presented in Tables 3 and 4 below, Table 3 corresponding to the results obtained for the tests having been carried out with hexanal oxime (BX1 to BX5, BX8 and BX10) and Table 4 corresponding to results obtained for the tests carried out with pentanal oxime (BX6 and BX7). Table 3 testing Composition of the phases Initial phases Final Phases (U (IV) / Pu) _initial U (IV) _cons. / Pu _dice. FD _Pu Aqueous phase Organic phase Aqueous phase Organic phase BX1 [U (VI)] (g / L) 9.9 71 26.9 0.85 0.6 53 [U (IV)] (g / L) 13.25 1.6 2.5 [Pu (IV)] (g / L) 7.8 [Pu (III)] (g / L) 13.3 [Pu] (g / L) 0,147 [HNO ₃ ] (mol / L) 1 [NH] (mol / L) 0,015 [hexanal oxime] (mol / L) 0.1 BX2 [U (VI)] (g / L) 9.9 74 13.5 1.46 0.55 58 [U (IV)] (g / L) 13.25 3.8 2.5 [Pu (IV)] (g / L) 4.23 [Pu (III)] (g / L) 8.16 [Pu] (g / L) 0,072 [HNO ₃ ] (mol / L) 1 [NH] (mol / L) 0,015 [hexanal oxime] (mol / L) 0.1 BX3 [U (VI)] (g / L) 9.9 70.8 36.7 76.4 0.99 0.49 17 [U (IV)] (g / L) 13.25 1.4 1.6 [Pu (IV)] (g / L) 6.7 [Pu (III)] (g / L) 13.8 [Pu] (g / L) 0.39 [HNO ₃ ] (mol / L) 1 [NH] (mol / L) 0.02 [hexanal oxime] (mol / L) 0.09 BX5 [U (VI)] (g / L) 10.2 59.2 65.6 0.96 0.6 156 [U (IV)] (g / L) 12 1.6 [Pu (IV)] (g / L) 6.25 [Pu (III)] (g / L) 14.7 [Pu] (g / L) 0.04 [HNO ₃ ] (mol / L) 2 [NH] (mol / L) 0,015 [hexanal oxime] (mol / L) 0.1 BX8 [U (VI)] (g / L) 18.2 71.1 20.7 46.8 2 1 9 [U (IV)] (g / L) 4.2 6.9 1.5 [Pu (IV)] (g / L) 4.6 [Pu (III)] (g / L) 10.9 [Pu] (g / L) 0.5 [HNO ₃ ] (mol / L) 2 [NH] (mol / L) [hexanal oxime] (mol / L) 0.05 BX10 [U (VI)] (g / L) 0 71.1 20.7 46.8 2 1 9 [U (IV)] (g / L) 17.9 6.9 1.5 [Pu (IV)] (g / L) 4.6 [Pu (III)] (g / L) 10.9 [Pu] (g / L) 0.5 [HNO ₃ ] (mol / L) 1.5 [NH] (mol / L) [hexanal oxime] (mol / L) 0.1 [Tc] (mg / L) 80 testing Composition of the phases Initial phases Final Phases (U (IV) / Pu) _initial U (IV) _cons. / Pu _dice. FD _Pu Aqueous phase Organic phase Aqueous phase Organic phase BX6 [U (VI)] (g / L) 9.9 59.8 34.7 54.1 1.57 0.57 350 [U (IV)] (g / L) 13.25 5.8 1.3 [Pu (IV)] (g / L) 4.25 [Pu (III)] (g / L) 8.09 [Pu] (g / L) 0.012 [HNO ₃ ] (mol / L) 1 [NH] (mol / L) 0,015 [pentanal oxime] (mol / L) 0.1 BX7 [U (VI)] (g / L) 8.7 57 42.9 45 1.13 0.82 202 [U (IV)] (g / L) 14.1 1.2 1.3 [Pu (IV)] (g / L) 6.25 [Pu (III)] (g / L) 14.7 [Pu] (g / L) 0.031 [HNO ₃ ] (mol / L) 1 [NH] (mol / L) 0,015 [pentanal oxime] (mol / L) 0.1

• pour une concentration d'hexanal oxime de 0,1 mol/L en phase organique et pour un rapport massique (U(IV)/Pu) initial allant de 0,8 à 1,5, la quantité d'uranium(IV) consommé ramenée à la quantité de plutonium désextrait (rapport U(IV)_cons./Pu_dés.) est comprise entre 0,5 et 0,6 ; les phénomènes parasites de réoxydation du plutonium sont donc très faibles, voire inexistants ; ces résultats ont été observés pour des phases aqueuses présentant une concentration d'acide nitrique de 1 mol/L ou de 2 mol/L (essais BX1 à BX5) ;
• une diminution de moitié de la concentration d'hexanal oxime en phase organique (0,05 mol/L versus 0,1 mol/L) ainsi que la présence de technétium en phase aqueuse conduisent à une consommation d'uranium(IV) plus importante (rapport U(IV)_cons./Pu_dés. = 1) mais qui reste toutefois modérée (essais BX8 et BX10) ;
• la pentanal oxime permet de limiter également les phénomènes redox conduisant à une consommation supplémentaire d'uranium(IV), avec des performances cependant légèrement en retrait par rapport à celles obtenues avec l'hexanal oxime puisque le rapport U(lV)_cons./Pu_dés. obtenu avec la pentanal oxime est compris entre 0,6 et 0,8 (essais BX8 et BX10).

As these tables show:

• for a concentration of hexanal oxime of 0.1 mol / L in the organic phase and for an initial mass ratio (U (IV) / Pu) ranging from 0.8 to 1.5, the quantity of uranium (IV) consumed reduced to the amount of plutonium back-extracted (. U ratio (IV) _cons ./Pu _dice) is between 0.5 and 0.6; the parasitic phenomena of reoxidation of plutonium are therefore very weak, or even non-existent; these results were observed for aqueous phases with a nitric acid concentration of 1 mol / L or 2 mol / L (tests BX1 to BX5);
• a halving of the concentration of hexanal oxime in the organic phase (0.05 mol / L versus 0.1 mol / L) and the presence of technetium in the aqueous phase lead to a higher consumption of uranium (IV) (U (IV) ratio _cons / Pu _dice = 1) but which remains moderate however (tests BX8 and BX10);
• pentanal oxime also makes it possible to limit the redox phenomena leading to an additional consumption of uranium (IV), with performances slightly lower than those obtained with hexanal oxime since the ratio U (IV) _cons. / Pu _dice. obtained with pentanal oxime is between 0.6 and 0.8 (tests BX8 and BX10).

Moreover, the evolution of the uranium (IV) concentrations in the organic phases as obtained after the BX5, BX10 and BX6 tests was followed spectrophotometrically (λ = 653 nm) at intervals of time on a period of several hours.

The results of these follow-ups are illustrated on the figures 7 , 8 and 9 which respectively correspond to the organic phases BX5, BX10 and BX6.

These figures confirm the ability of pentanal oxime and hexanal oxime to stabilize uranium (IV) in the organic phase. This stabilization is less in the presence of technetium but the oxidation kinetics of uranium (IV) is relatively slow since there is a halving of the concentration of uranium (IV) in 50 minutes.

EXAMPLE 4 Development of a treatment scheme for a dissolution liquor of a spent nuclear fuel comprising a partition stage U / Pu without the use of hydrazine

A treatment scheme for a dissolution liquor of a spent nuclear fuel comprising a U / Pu partitioning step which is carried out without hydrazine but in which a hexanal oxime / acetaldoxime combination is used as an anti-nitrous system - hexanal oxime being used in organic phase and acetaldoxime being used in aqueous phase - was developed.

• d'une part, que l'acétaldoxime est réellement susceptible de remplacer l'hydrazine comme agent anti-nitreux en phase aqueuse, en présence de technétium ; et
• d'autre part, que l'hexanal oxime est aussi susceptible de stabiliser l'uranium(IV) dans la phase organique servant à réaliser l'opération dite « Lavage Np » qui, dans les procédés PUREX et COEX, sert à éliminer, de la phase aqueuse issue de l'opération de désextraction réductrice du plutonium, le neptunium ayant été désextrait au cours de cette opération.

Prior to the development of this scheme, it was verified:

• on the one hand, that acetaldoxime is really likely to replace hydrazine as an anti-nitrous agent in the aqueous phase, in the presence of technetium; and
• on the other hand, that hexanal oxime is also capable of stabilizing uranium (IV) in the organic phase used to carry out the so-called "Np wash" operation which, in the PUREX and COEX processes, serves to eliminate, the aqueous phase resulting from the reductive extraction operation of the plutonium, the neptunium having been desextracted during this operation.

4.1 - Anti-nitrous power of acetaldoxime in the aqueous phase and in the presence of technetium

Tests have been carried out to compare the anti-nitrous power in the aqueous phase of acetaldoxime with that of hydrazine and this in the presence of technetium.

• préparation de solutions aqueuses comprenant 9 g/L d'uranium(IV) et 2 mol/L d'acide nitrique ainsi que 0,2 mol/L d'acétaldoxime ou d'hydrazine, ces solutions étant thermostatées à 35°C ;
• ajout à ces solutions d'une solution aqueuse comprenant 8,88 g/L de technétium(VII) (soit 0,09 mol/L) pour atteindre des concentrations finales en technétium de 100 mg/L ou 200 mg/L; et après agitation
• suivi des cinétiques d'oxydation de l'uranium(IV) dans lesdites solutions aqueuses par des mesures spectrophotométriques (λ = 653 nm) sur une période de 100 minutes.

To do this, we followed the following operating protocol:

• preparation of aqueous solutions comprising 9 g / l of uranium (IV) and 2 mol / l of nitric acid and 0.2 mol / l of acetaldoxime or of hydrazine, these solutions being thermostatically controlled at 35 ° C .;
• adding to these solutions an aqueous solution comprising 8.88 g / L of technetium (VII) (ie 0.09 mol / L) to reach final concentrations of technetium of 100 mg / L or 200 mg / L; and after stirring
• monitoring oxidation kinetics of uranium (IV) in said aqueous solutions by spectrophotometric measurements (λ = 653 nm) over a period of 100 minutes.

The results of these tests are illustrated on the figure 10 in which the results obtained for acetaldoxime in the presence of 100 mg / L and 200 mg / L of Tc respectively correspond to the symbols ■ and × while the results obtained for hydrazine in the presence of 100 mg / L and 200 mg / L correspond to the symbols ▲ and ●, respectively.

As shown in this figure, the anti-nitrous power of acetaldehyde oxime is, in the aqueous phase and in the presence of 100 mg or 200 mg of technetium, comparable to that of hydrazine.

It is therefore possible to replace hydrazine, as an anti-nitrous agent in the aqueous phase, with acetaldoxime.

4.2 - Stabilization of uranium (IV) in the operation "Wash Np"

• comme phases organiques : des solutions de TBP à 30% (v/v) dans du TPH, comprenant ou non 0,1 mol/L d'hexanal oxime ; et
• comme phases aqueuses : des solutions aqueuses à 1,3 mol/L d'acide nitrique, comprenant de l'uranium(IV), de l'acétaldoxime, du plutonium(III) et du technétium aux concentrations indiquées dans le tableau 5 ci-après ; le technétium a été ajouté aux phases aqueuses juste avant leur mise en contact avec les phases organiques, sous la forme d'une solution concentrée de Tc(VII) à 8,88 g/L.

Two tests, noted below BS16 and BS17, were performed using:

• as organic phases: TBP solutions at 30% (v / v) in TPH, with or without 0.1 mol / L hexanal oxime; and
• as aqueous phases: aqueous solutions containing 1.3 mol / L of nitric acid, comprising uranium (IV), acetaldoxime, plutonium (III) and technetium at the concentrations indicated in Table 5 below. after; technetium was added to the aqueous phases just prior to contact with the organic phases as a concentrated solution of Tc (VII) at 8.88 g / L.

The organic phases and aqueous phases were brought into contact, volume-to-volume, for 15 minutes, at room temperature (20-25 ° C.) and with stirring, and then these phases were separated from each other.

The concentrations of uranium (IV) in the aqueous and organic phases were measured and the percentage of uranium (IV) consumed during each test, noted U (IV) _cons. , has been determined.

The results are shown in Table 5 below.

This table shows that the presence of hexanal oxime in the organic phase (test BS16) makes it possible to reduce the consumption of uranium (IV) by 50% compared to what it is in the absence of this oxime (test BS17). Table 5 testing Composition of the phases Initial phases Final Phases U (IV) _cons. (%) Aqueous phase Organic phase Aqueous phase Organic phase BS16 [U (VI)] (g / L) 18 [U (IV)] (g / L) 36.5 19 10.7 [Pu (IV)] (g / L) [Pu (III)] (g / L) 12.3 12.1 [Pu] (g / L) [HNO ₃ ] (mol / L) 1.3 [acetaldoxime] (mol / L) 0.27 [hexanal oxime] (mol / L) 0.1 [Tc] (mg / L) 77 BS17 [U (VI)] (g / L) 39 [U (IV)] (g / L) 36.1 16.5 6.3 [Pu (IV)] (g / L) [Pu (III)] (g / L) 12.6 [Pu] (g / L) [HNO ₃ ] (mol / L) 1.3 [acetaldoxime] (mol / L) 0.27 [hexanal oxime] (mol / L) 0 [Tc] (mg / L) 77

4.3 - Treatment schema

The treatment scheme of a spent fuel dissolution liquor that has been developed is illustrated on the figure 11 .

1. (1) une étape qui permet de décontaminer l'uranium et le plutonium vis-à-vis des actinides(III) (américium et curium) et d'un certain nombre de produits de fission et qui comprend :
   • * une opération, dénommée « Co-extraction U/Pu » sur la figure 11, qui vise à extraire conjointement l'uranium, le plutonium et le neptunium, le premier à l'état d'oxydation VI, le second à l'état d'oxydation IV et le troisième à l'état d'oxydation VI, de la liqueur de dissolution au moyen d'une phase organique comprenant du TBP à 30% (v/v) dans du TPH ;
   • * une opération, dénommée « Lavage PF » sur la figure 11, qui vise à retirer de la phase organique issue de l'opération « Co-extraction U/Pu » des produits de fission et, en particulier, le ruthénium et le zirconium, ayant été extraits au cours de la « Co-extraction U/Pu » ;
   • * une opération, dénommée « Lavage Tc » sur la figure 11, qui vise à retirer de la phase organique issue du « Lavage PF » le technétium ayant été extrait au cours de la « Co-extraction U/Pu » au moyen d'une phase aqueuse ; ainsi qu'
   • * une opération, dénommée « Co-extraction complém. U/Pu » sur la figure 11, qui vise à récupérer en phase organique les fractions d'uranium(VI), de plutonium(IV) et de neptunium ayant suivi le technétium en phase aqueuse au cours du « Lavage Tc » ; et
2. (2) une étape qui permet de réaliser une partition de l'uranium et du plutonium en deux flux aqueux, l'un contenant de l'uranium et l'autre contenant le plutonium et de l'uranium (dans un rapport massique U/Pu de l'ordre de 20/80 à 30/70) et qui comprend :
   • * une opération, dénommée « Désextraction Pu/U » sur la figure 11, qui vise à désextraire le plutonium de la phase organique issue du « Lavage Tc » ainsi qu'une fraction de l'uranium présent dans cette phase organique, cette opération étant réalisée au moyen d'une phase aqueuse comprenant de l'uranium(IV) comme agent réducteur propre à réduire le plutonium à l'état d'oxydation III ;
   • * une opération, dénommée « Lavage Np » sur la figure 11, qui vise à retirer de la phase aqueuse issue de la « Désextraction Pu/U » l'uranium en excès par rapport au rapport massique U/Pu visé de 20/80 à 30/70, et la fraction de neptunium ayant suivi le plutonium en phase aqueuse au cours de la « Désextraction Pu/U » ; et
   • * une opération, dénommée « Désextraction U », qui vise à désextraire de la phase organique issue de la « Désextraction Pu/U » l'uranium et le neptunium au moyen de la phase aqueuse.

In this diagram, we find the two main stages of the first cycle of purification of the COEX process, namely:

1. (1) a step for decontaminating uranium and plutonium with respect to actinides (III) (americium and curium) and a number of fission products and which comprises:
   • * an operation, called "Co-extraction U / Pu" on the figure 11 , which aims at jointly extracting uranium, plutonium and neptunium, the first in the oxidation state VI, the second in the oxidation state IV and the third in the oxidation state VI, the dissolution liquor using an organic phase comprising 30% (v / v) TBP in TPH;
   • * an operation, called "PF wash" on the figure 11 , which aims at removing from the organic phase resulting from the operation "Co-extraction U / Pu" fission products and, in particular, ruthenium and zirconium, having been extracted during the "Co-extraction U / Could ";
   • * an operation, called "Tc wash" on the figure 11 which aims at removing from the organic phase resulting from the "PF wash" the technetium which has been extracted during the "U / Pu Co-extraction" by means of an aqueous phase; as well as'
   • * an operation, called "Co-extraction complém. U / Pu "on the figure 11 , which aims to recover in the organic phase the fractions of uranium (VI), plutonium (IV) and neptunium having followed the technetium in the aqueous phase during the "Tc wash"; and
2. (2) a step that makes it possible to partition uranium and plutonium into two aqueous streams, one containing uranium and the other containing plutonium and uranium (in a mass ratio U / Pu of the order of 20/80 to 30/70) and which comprises:
   • * an operation, called "Pu / U Desextraction" on the figure 11 , which aims to extract the plutonium from the organic phase resulting from the "Tc wash" and a fraction of the uranium present in this organic phase, this operation being carried out using an aqueous phase comprising uranium (IV ) as a reducing agent capable of reducing the plutonium in the oxidation state III;
   • * an operation, called "Wash Np" on the figure 11 , which aims to remove from the aqueous phase resulting from the "Pu / U Desextraction" the uranium in excess with respect to the U / Pu mass ratio target of 20/80 to 30/70, and the fraction of neptunium that followed the plutonium in the aqueous phase at course of "Pu / U Desextraction"; and
   • * an operation, called "U-Desextraction", which aims to extract the organic phase resulting from the "Pu / U Desextraction" uranium and neptunium by means of the aqueous phase.

However, in the diagram shown on the figure 11 the hydrazine, which is the anti-nitrous agent used in the COEX process, is replaced by a hexanal oxime / acetaldoxime combination.

As visible on the figure 11 , hexanal oxime (denoted HexOx on the figure 11 ) is introduced, given its highly lipophilic character, in the organic phase entering the extractor 5 in which the "Np wash" takes place and in the organic phase from the "Tc wash", just before that. it does not enter the extractor 6.

Acetaldoxime (denoted AcOx on the figure 11 ), it is introduced, given its hydrophilic nature, in the aqueous phase circulating in the extractor 6, this introduction being carried out at three different stages of this extractor: the stage 8 at which it is injected into the aqueous phase for the desextraction and stages 1 and 4 at which the acetaldoxime is injected into the aqueous streams used to supply this aqueous phase uranium (IV).

The elementary acquisitions concerning the oximes implemented in the two phases, aqueous and organic, were used to develop first models to simulate their partitioning between the aqueous and organic phases implemented in the process as well as their kinetics of reaction with nitrous acid. These models have been implemented in the PAREX code which is a software for simulating the sharing of species of interest in operations such as those of partitioning uranium and plutonium into two aqueous streams. It is on the basis of this simulation that the operating parameters in which the diagram illustrated on the figure 11 has been tested experimentally.

The figure 12 compare the concentration profiles of uranium (IV) in the aqueous phases circulating in the extractors 5 and 6 as calculated for, on the one hand, the diagram illustrated on the figure 11 (curve A) and, on the other hand, for a homologous scheme using hydrazine (curve B). The ideal profile, obtained by neutralizing (in the PAREX code) the reoxidation reactions of plutonium (III) is also represented (curve C).

As shown in this figure, the use of a hexanal oxime / acetaldoxime combination leads to a profile of uranium (IV) concentrations higher than that obtained with hydrazine, thus confirming the decrease in the consumption of the substance. uranium (IV) in the presence of these oximes.

The diagram shown on the figure 11 has been successfully implemented, in ATALANTE's shielded process cell, on a real solution of a spent nuclear fuel. This scheme made it possible to produce a plutonium stream with a concentration of 10 g / L with a consequent concentration of uranium (IV) (16 g / L), and this, without any additional uranium (IV) in the operation. "Np wash" while this supplement is necessary in the homologous scheme using hydrazine. Uranium (IV) consumption is also lower than in the hydrazine regimen.

The figure 13 illustrates the profiles of the concentrations of plutonium in the aqueous phases circulating in extractors 5 and 6, as obtained experimentally (symbol ×) and as calculated by the code PAREX (curve -), while the figure 14 illustrates the concentration profiles of uranium (IV), uranium (VI) and total uranium of the aqueous phases circulating in these same extractors, as obtained experimentally and by calculations; in this figure, the symbols ×, ◆ and ■ respectively correspond to the profiles of the concentrations of uranium (IV), uranium (VI) and total uranium obtained experimentally, while the curves A, B and C correspond respectively to the profiles of the concentrations of uranium (IV), uranium (VI) and total uranium obtained by calculations.

In addition, the concentration of uranium in the aqueous phase from extractor 5 (denoted by [U (IV)] ( _Pu ) _production is shown in Table 6 below, the concentration of plutonium in the aqueous phase extractor 5 (denoted [Pu] Pu _{production flow} ), the ratio between the flow of uranium (IV) introduced into the extractor 6 and the flow of Pu introduced into this same extractor (noted U (IV) / Pu _introduced ), the percentage of uranium (IV) consumed (noted U (IV) _cons. ) And the ratio between the flow of uranium (IV) consumed and the flux of plutonium introduced (noted U (IV) _cons / Pu) as obtained experimentally for the diagram illustrated on the figure 11 .

By way of comparison, these same concentrations, ratios and percentages are also presented in this table, but as obtained experimentally for the homologous scheme using hydrazine. Table 6 Diagram of the figure 11 Hydrazine diagram [U (IV)] _{Pu production flow} (g / L) 16 2.4 [PU] _{Pu workflow} (g / L) 10 10.7 U (IV) / Pu _introduced 3.8 3.8 U (IV) _cons. (%) 59 75 U (IV) _cons. /Could 2.3 2.7

REFERENCES CITED

1. [1] WO-2006/072729
2. [2] WO-2011/000844
3. [3] WO-2008/148863

Claims (12)

1. Use of at least one aldoxime of formula R-CH=N-OH where R is a linear or branched hydrocarbon chain having at least 4 carbon atoms, as anti-nitrous agent in a reductive stripping operation of plutonium.
2. Use according to claim 1, wherein R is a linear or branched hydrocarbon chain having 4 to 12 carbon atoms and, better still, 4 to 8 carbon atoms.
3. Use according to claim 2, wherein R is a linear alkyl chain having 4 to 8 carbon atoms.
4. Use according to claim 3, wherein the aldoxime is pentanal oxime or hexanal oxime.
5. Use according to any of claims 1 to 4, wherein the reductive stripping operation of plutonium comprises:

   - contacting an organic non-water-miscible phase comprising an extracting agent and plutonium at oxidation state IV in an organic diluent, with an aqueous phase comprising a reducing agent capable of reducing plutonium(IV) to plutonium(III) and nitric acid, one of the organic and aqueous phases also comprising the aldoxime; then

   - separating the so contacted organic and aqueous phases.
6. Use according to claim 5, wherein the reducing agent is selected from among uranium(IV), hydroxylammonium nitrate, alkylated derivatives of hydroxylamine, ferrous sulfamate and sulfamic acid.
7. Use according to claim 6, wherein the reducing agent is uranium(IV) or hydroxylammonium nitrate.
8. Use according to any of claims 5 to 7, wherein the extracting agent is a tri-n-alkyl phosphate, preferably tri-n-butyl phosphate.
9. Use according to any of claims 1 to 8, wherein the aldoxime is used at a concentration of 0.01 mol/L to 3 mol/L of organic or aqueous phase.
10. Use according to any of claims 5 to 9, wherein the aqueous phase additionally comprises an oxime that is non-extractable by the organic phase.
11. Use according to claim 10, wherein the oxime that is non-extractable by the organic phase is acetaldoxime.
12. Use according to any of claims 1 to 11, wherein the reductive stripping operation of plutonium is one of the plutonium stripping operations of the PUREX method or COEX method.

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