CN108369828B

CN108369828B - Use of an aldoxime containing at least five carbon atoms as an anti-nitrosating agent in plutonium reducing stripping operations

Info

Publication number: CN108369828B
Application number: CN201680065527.XA
Authority: CN
Inventors: 宾赫·迪恩; 帕特里克·波雄; 吉勒斯·贝尼耶; 科拉列·巴拉格尔; 马克·蒙图伊
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2015-10-21
Filing date: 2016-10-18
Publication date: 2022-05-24
Anticipated expiration: 2036-10-18
Also published as: JP2018536847A; JP6876688B2; WO2017067933A1; FR3042904B1; FR3042904A1; RU2018118245A3; RU2018118245A; EP3365897A1; RU2718437C2; EP3365897B1; CN108369828A

Abstract

The present application relates to the use of an aldoxime containing at least five carbon atoms as an anti-nitrous acidifier in plutonium reducing stripping operations. The present application is applicable to any process for treating spent fuel that includes one or more plutonium reduction stripping operations, and is particularly applicable to the PUREX process as practiced in modern plants for treating spent fuel, and to processes derived therefrom.

Description

Use of an aldoxime containing at least five carbon atoms as an anti-nitrosating agent in plutonium reducing stripping operations

Technical Field

The present application relates to the field of treating spent fuel.

More particularly, the present application relates to the use of aldoximes having at least five carbon atoms as anti-nitrosative agents in plutonium reducing stripping operations.

The present application is applicable to any process for treating spent fuel that includes one or more plutonium reducing stripping operations.

Said operations are particularly included in the PUREX process, such as the processes carried out in modern nuclear fuel processing plants (i.e. the UP3 and UP2-800 plants of laja francis, and the six village plants of japan), which firstly carry out the U/Pu distribution step of the first decontamination cycle, and secondly improve the plutonium decontamination of the fission products in the plutonium decontamination cycle after the first decontamination cycle (generally referred to as the "second plutonium cycle").

Said operation is also included in a number of methods derived from the PUREX process, such as the method described in International application PCT WO 2006/072729[1] (known as the COEX process), or the method described in International application PCT WO 2011/000844[2 ].

Background

In the plutonium reduction stripping operation carried out in the aforementioned spent fuel processing method, plutonium is transferred from its organic phase (or solvent phase) in oxidation state IV into the aqueous phase by reducing it to oxidation state III, in which state plutonium has very low affinity for the organic phase.

A reducing agent is added to the aqueous phase for stripping and stabilized with an anti-nitrite acidifying agent, which induces the reduction of plutonium (IV) to plutonium (III).

For the first decontamination cycle of the PUREX process (which will be referred to simply as "PUREX process" in the remainder of the text), as implemented for example in modern nuclear fuel reprocessing plants, the reducing agent used to strip the plutonium in the U/Pu partitioning step is uranium (IV) (or uranium nitrate), while the anti-nitrifying agent is hydrazine nitrate (also known as hydrazine).

The main chemical reactions to be considered are:

reduction of plutonium (IV) to plutonium (III) using uranium (IV) (functional reaction):

U⁴⁺+2Pu⁴⁺+2H₂O→UO₂ ²⁺+2Pu³⁺+4H⁺

reoxidation of the plutonium (III) to plutonium (IV) (parasitic reaction):

Pu³⁺+HNO₂+1.5H⁺+0.5NO₃ ^-→Pu⁴⁺+0.5H₂O+1.5HNO₂

nitrous acid is destroyed to azido acid using hydrazine (useful reaction):

N₂H₅NO₃+HNO₂→N₃H+HNO₃+2H₂O.

the first two reactions occur in the aqueous and organic phases, whereas the nitrous acid destruction reaction of hydrazine occurs only in the aqueous phase, since hydrazine cannot be extracted by the organic phase consisting of 30% (v/v) tri-n-butyl phosphate (or TBP) in tetrapropene (or HTP) hydride.

The presence of plutonium (III) in the organic phase, even in small amounts, catalyzes the oxidation of uranium (IV) by the first two reactions, producing nitrous acid.

It can be determined that in experimental studies carried out in laboratory centrifuge extractors, the consumption of uranium (IV) by oxidation is very high even if the extractor residence time is short (of the order of a few seconds). Oxidation of uranium (IV) occurs primarily in the organic phase, as hydrazine is only contained in the aqueous phase. As a result, the plutonium reducing stripping protocol provides a large excess of reductant.

The hydrazoic acid formed from nitrous acid via the hydrazine destruction reaction reacts in turn with nitrous acid according to the following reaction:

HN₃+HNO₂→N₂+N₂O+H₂O。

however, the kinetics of this reaction are much slower than the destruction of nitrous acid by hydrazine, which means that the azido acid appears in the effluent aqueous and organic phases of the U/Pu partitioning step.

Thus, since hydrazine cannot be extracted by the organic phase and therefore only works in the aqueous phase, this leads to a high consumption of reagents and to chemicals which hamper the industrial application of the process.

To solve this problem, the use of a two-phase nitrous acid resistant system combining butyraldehyde oxime (also known as butyraldehyde oxime or butyraldoxime) with hydrazine, the butyraldehyde oxime stabilizing the organic phase and the hydrazine stabilizing the aqueous phase, is proposed in International application PCT WO 2008/148863[3 ].

Although the use of butyraldehyde oxime in combination with hydrazine has a number of advantages, in particular it allows to significantly reduce the amount of uranium nitrate and hydrazine required to carry out the plutonium reduction reaction, with consequent reduction of the drawbacks linked to the non-extraction of hydrazine in the organic phase, which is not entirely satisfactory, because:

the extraction of organic phase with respect to butyraldehyde oxime is relatively low, and if it is desired to obtain an effective concentration of butyraldehyde oxime in the organic phase, it is necessary to add a large amount of this oxime to the extractor where the plutonium reducing back-extraction takes place; in particular in the U/Pu partitioning step, the extraction of the organic phase with respect to butyraldehyde oxime is greatly reduced by saturating this phase with actinides, eventually making the use of this oxime hardly suitable for carrying out the partitioning step;

continuous use of hydrazine in the aqueous phase; indeed, although hydrazine is one of the most effective anti-nitrosating agents in the aqueous phase, its use is limited not only by the problems associated with the formation of hydrazoic acid indicated above, but also by its toxicity: hydrazine is in fact on the CMR list of substances, i.e. substances that are considered or proved to be carcinogenic, mutagenic and/or reproductive toxic according to the regulations (EC)1907/2006(REACH regulation) for the registration, evaluation, licensing and restriction of chemicals, and it is likely that in time it will enter the list of substances authorized in appendix XIV of this regulation, in which case its sale and industrial use will be banned unless a specific exemption is given by the european chemical authority (ECHA).

In addition, the reaction of butyraldehyde oxime with hydrazine was also observed, forming a hydrazone. This reaction reduces the performance of butyraldehyde oxime and results in excessive consumption of both reagents.

In view of the above, the applicant therefore set out to find compounds with high resistance to nitrous acid, but using them without the drawbacks deriving from the use of hydrazine, such as currently used in the PUREX process, or from the use of a two-phase butyraldehyde oxime/hydrazine system, such as proposed in reference [3 ].

More specifically, they set the goal of: even in the case where the actinides saturate the organic phase, these compounds should be more easily extracted (under the same conditions of temperature and pressure) by the organic phase (in particular of the type used in the PUREX process) than by hydrazine, in order to be able to: (1) reducing the amount of these compounds required for the plutonium reduction reaction, and (2) using these compounds for the plutonium stripping in the U/Pu partitioning step of the first purification cycle of the PUREX process and in the plutonium stripping in the second plutonium cycle of the process.

They also set the goal: these compounds should completely circumvent the use of hydrazine.

Disclosure of Invention

These and other objects are achieved by the present application which proposes the use, in a plutonium reducing stripping operation, of at least one aldoxime having at least 5 carbon atoms, i.e. an oxime of the general formula R-CH ═ N-OH, wherein R is a hydrocarbon chain having at least 4 carbon atoms, as an anti-nitrosating agent.

Preferably, the aldoxime corresponds to the above formula wherein R comprises up to 12 carbon atoms and advantageously up to 8 carbon atoms.

More preferably, the aldoxime corresponds to the above general formula wherein R is a linear alkyl chain having 4 to 8 carbon atoms.

The aldoxime is of the formula n-C₄H₉Valeraldoxime (also known as valedaldehydeoxime or valedaldoxime) of the formula N-C, with-CH ═ N-OH₅H₁₁(iii) hexanaldoxime of-CH ═ N-OH, formula N-C₆H₁₃-heptaldoxime with-CH ═ N-OH of formula N-C₇H₁₅Octanoyl oximes of-CH ═ N-OH and of the formula N-C₈H₁₇Nonanal oximes of-CH-N-OH.

Among these aldoximes, valeraldoxime and caproaldoxime are particularly preferable.

According to the present application, the plutonium reduction stripping operation preferably comprises:

contacting an organic non-aqueous miscible phase comprising in an organic diluent an extractant and plutonium in oxidation state IV with an aqueous phase comprising a reducing agent capable of reducing plutonium (IV) to plutonium (III) and nitric acid, the aldoxime being contained in the organic phase or in the aqueous phase depending on its solubility in water; then the

The organic and aqueous phases thus contacted are separated.

Thus, the valeraldoxime, which is partially soluble in water (under the temperature and pressure conditions conventionally used in these operations) and partially soluble in the organic diluent that can be used in the plutonium reducing stripping operation, can be added to the aqueous phase or to the organic phase, while the aldoxime, having 6 or more carbon atoms, which is insoluble or practically insoluble in water (under the above conditions), is added to the organic phase.

In the present application, the reducing agent contained in the aqueous phase is preferably selected from uranium (IV), hydroxylamine nitrate (also known as hydroxylamine nitrate), alkylated derivatives of hydroxylamine, ferrous sulphamate or sulphamic acid.

Among these reducing agents, particular preference is given to uranium (IV) and hydroxylamine nitrate, which are the two reagents used in the PUREX process for reducing plutonium (IV) to plutonium (III), the first reagent being in the U/Pu distribution step of the purge cycle and the second reagent being in the second plutonium cycle.

Moreover, the extractant is preferably a tri-n-alkyl phosphate and better still TBP, while the organic diluent is preferably a linear or branched dodecane (such as n-dodecane or HTP), an isoparaffinic solvent (such as island IP185, island IP165 or Isopar L) or kerosene, in which case the extractant is preferably contained in the organic diluent in a proportion of 30% (v/v).

In any case, the aldoxime is used in an organic phase or an aqueous phase at a concentration of preferably 0.01 to 3mol/L, more preferably 0.05 to 0.5 mol/L; and the concentration of the reducing agent used in the aqueous phase is preferably 0.02 to 0.6mol/L, and still more preferably 0.2 to 0.4 mol/L.

As regards the nitric acid, it is advantageously contained in the aqueous phase in a concentration of between 0.05 and 2 mol/L.

In the present application, if an aldoxime has an equilibrium distribution between the organic phase and the aqueous phase when the organic phase and the aqueous phase are brought into contact with each other, the aldoxime can be used as the only anti-nitrosating agent in the plutonium reducing stripping operation. However, if this is not the case for aldoximes having 6 or more carbon atoms (such as hexanal oxime or octanal oxime) which normally occur due to their high extraction by the organic phase (under the conditions of temperature and pressure conventionally used for plutonium reducing stripping operations), the aldoxime is advantageously used in combination with a second nitrous acid reagent which is an oxime which (under the same conditions of temperature and pressure) cannot be extracted by the organic phase.

At this pointIn this case, the non-extractable oxime contained in the aqueous phase is preferably of the formula CH₂Formaldoxime (also known as formaldehydeoxime) of formula CH — OH or CH₃-CH ═ N-OH aldoxime (also known as acetoaldehyde oxime), and its concentration used in the aqueous phase is advantageously between 0.01 and 1mol/L and still more preferably between 0.05 and 0.2 mol/L.

According to a particularly preferred embodiment of the present application, the plutonium reducing stripping operation is preferably one of plutonium stripping operations of the PUREX process or the COEX process.

The present application provides a number of advantages. It provides a series of anti-nitrite acidulants (some used alone, while others are used in combination with an organic phase non-extractable oxime) that are most effective in blocking the re-oxidation of plutonium (III) to plutonium (IV) in both the organic and aqueous phases.

Thus, in addition to the fact that the present application enables plutonium reducing stripping operations to be carried out without using hydrazine, it also enables the quantities of reducing agent and anti-nitrous acidifying agent required for these operations to be reduced very substantially compared to the quantities required when the anti-nitrous acidifying agent is hydrazine, both for operations carried out in a U/Pu separation step as in the PUREX process and for operations carried out in a second plutonium cycle as in the same process.

The present application therefore considers that it is possible to reduce the number of points (number of points) required to add these anti-nitrous acidifiers to a plant dedicated to plutonium reducing stripping operations, and thus to simplify the plant.

Furthermore, the present application also envisages a reduction in the size of the plants currently used for the plutonium reduction stripping operation, since plutonium stripping is more efficient and therefore obtains an aqueous phase with a higher plutonium concentration at the end of the stripping operation, compared to the case of using hydrazine as anti-nitrous acidifying agent.

Other features and other advantages of the present application will become more apparent upon reading the following examples.

It is clear that these examples are given only as illustrations of the subject matter of the application and do not limit the application in any way.

Drawings

FIG. 1 shows the distribution coefficients of valeraldoxime (■ notation) and aldoxime (● notation) between an organic phase containing TBP in n-dodecane and an aqueous phase containing different concentrations of nitric acid; for comparison, the figure also shows the distribution coefficient obtained for butyraldehyde oxime (. tangle-solidup.) under the same conditions.

Fig. 2A and 2B show the distribution coefficients of valeraldoxime (■ symbols) and caproaldoxime (● symbols) between the organic and aqueous phases, which simulate the organic and aqueous phases obtained in the U/Pu separation step of the PUREX process, in terms of uranium (VI) concentration and nitric acid concentration.

FIG. 3 shows the kinetics of destruction of valeraldoxime (curve A) to nitrous acid in an aqueous nitric acid phase; for comparison, the figure also shows the kinetics of destruction of nitrous acid by butyraldehyde oxime (curve B) and acetaldoxime (curve C) obtained under the same conditions.

FIG. 4 shows the kinetics of destruction of valeraldoxime (curve A) and hexaaldoxime (curve B) to nitrous acid in an organic phase containing TBP in n-dodecane; for comparison, the figure also shows the kinetics of destruction of butyraldehyde oxime (curve C) to nitrous acid obtained under the same conditions.

Figure 5 shows the kinetics of oxidation of uranium (IV) obtained in the presence of valeraldoxime (curve a) and caproaldoxime (curve B) in an organic phase containing TBP in n-dodecane, after contacting these organic phases with an aqueous nitric acid solution and subsequent separation of these phases; for comparison, the figure also shows the kinetics of oxidation of uranium (IV) obtained under the same conditions in the presence of butyraldehyde oxime (curve C) and in the absence of any oxime (curve D).

Figure 6 shows the kinetics of oxidation of uranium (IV) obtained in aqueous nitric acid solution in the presence of valeraldoxime (curve a); for comparison, the figure also shows the kinetics of oxidation of uranium (IV) obtained under the same conditions in the presence of butyraldehyde oxime (curve B), acetaldoxime (curve C) and hydrazine (curve D).

Figure 7 shows the kinetics of oxidation of uranium (IV) contained in the organic phase (TBP/HTP) after a plutonium reducing stripping test in which hexanal oxime was used as anti-nitrosating acidifier.

Fig. 8 shows the kinetics of oxidation of uranium (IV) contained in the organic phase (TBP/HTP) after a plutonium reductive stripping test in which hexanal oxime was used as anti-nitrosating agent and technetium was co-stripped with plutonium.

Figure 9 shows the kinetics of oxidation of uranium (IV) in the organic phase (TBP/HTP) after plutonium reducing stripping test with valeraldoxime as an anti-nitrite acidifying agent.

FIG. 10 shows the kinetics of uranium (IV) oxidation in the presence of acetaldoxime in an aqueous nitric phase containing 100mg/L (■ symbols) or 200mg/L (× symbols) technetium; for comparison, the figure also shows the kinetics of oxidation of uranium (IV) obtained under identical conditions in the presence of hydrazine and 100mg/L (. tangle-solidup.) or 200mg/L (● symbol) technetium.

FIG. 11 shows a scheme for treating spent fuel dissolving liquor including a U/Pu dispensing step with hexaaldoxime/acetaldoxime combination as an anti-nitritation system; in the figure, the rectangles labeled 1-7 represent multi-stage extractors such as those conventionally used for processing spent fuels (mixer-settlers, pulsed columns, centrifugal extractors); and the organic phase entering and leaving the extractors is indicated by a solid line, while the aqueous phase entering and leaving these extractors is indicated by a dashed line.

Figure 12 shows the distribution curve obtained by calculation of the uranium (IV) concentration in the aqueous phase circulating in the

extractors

5 and 6 of the solution shown in figure 11 (curve a); for comparison, the distribution curve of the uranium (IV) concentration obtained when hexanaldoxime and acetaldoxime were replaced with hydrazine in this scheme (curve B) and the distribution curve of the uranium (IV) concentration obtained when the reoxidation reaction of plutonium (III) was completely neutralized (curve C) are also given.

Fig. 13 shows the distribution curves of the plutonium concentration in the aqueous phase circulating in

extractors

5 and 6 of the scheme shown in fig. 11, obtained by experiment (x sign) and by calculation (curve-).

Fig. 14 shows the distribution curves of the uranium (IV), uranium (VI) and total uranium concentrations of the aqueous phase circulating in the

extractors

5 and 6 of the scheme shown in fig. 11, obtained for example by experiment and by calculation; in the figure, symbols x, diamond-solid, and ■ correspond to distribution curves of uranium (VI), uranium (IV), and total uranium concentrations obtained by experiments, respectively, and curves A, B and C correspond to uranium (VI), uranium IV, and total uranium concentrations obtained by calculation, respectively.

Detailed Description

Example 1: properties of valeraldoxime and caproaldoxime

1.1–Coefficient of distribution

The distribution coefficients of valeraldoxime and caproaldoxime (expressed as D) were determined by the following two series of tests:

a first series for determining these distribution coefficients between an organic phase comprising 30% (v/v) TBP in n-dodecane and an aqueous phase comprising from 0.2 to 2mol/L nitric acid; and

the second series, for determining these distribution coefficients between the organic and aqueous phases, which simulated the organic and aqueous phases obtained in the U/Pu partitioning step of the PUREX process in terms of uranium (VI) concentration and nitric acid concentration, was carried out in a mixer-settler unit with 8 stages (denoted BX1 to BX 8).

For both series of tests, each organic phase was contacted with a volume of aqueous nitric acid solution at ambient temperature (20-25 ℃) with stirring for 15 minutes. Valeraldoxime was added to the aqueous phase and hexanaldoxime was added to the organic phase, both at a concentration of 0.1mol/L in the phases.

The contacted organic and aqueous phases were separated from each other by centrifugation and the concentration of aldoxime in these phases was measured by High Performance Liquid Chromatography (HPLC) for the aqueous phase and by gas chromatography (GPC) for the organic phase.

Table 1 below gives the distribution coefficients obtained in the first series of tests. They are also given in fig. 1, where the values shown in the table have been transposed and the distribution coefficient of valeraldoxime is represented by the symbol ■, while the distribution coefficient of caproaldoxime is represented by the symbol ●. For comparison, FIG. 1 also shows the distribution coefficient (. tangle-solidup.) of butyraldehyde oxime obtained under the same conditions.

TABLE 1

The distribution coefficients obtained in the second series of tests are given in table 2 below. They are also given in fig. 2A and 2B, where the values of the distribution coefficient (Y-axis) and the acidity value (X-axis) of the aqueous phase have been transposed (transpose) and the distribution coefficient of valeraldoxime corresponds to the sign ■ and the distribution coefficient of caproaldoxime corresponds to the sign ●. The ordinate in fig. 2A is a decimal number, while the ordinate in fig. 2B is a logarithmic number.

TABLE 2

As shown in table 1 and fig. 1, pentanal oxime and hexanal oxime showed distribution coefficients significantly higher than that of butyraldehyde oxime, which means that they are more easily extracted in the organic phase than butyraldehyde oxime.

If the aqueous phase contains actinides (table 2 and figures 2A and 2B), the distribution coefficients for valeraldoxime and caproaldoxime decrease compared to the values in the absence of actinides; however, they are still high enough that the valeraldoxime and caproaldoxime are still significantly extracted. Under the same conditions, the distribution coefficient of butyraldehyde oxime is lower than 1.

The distribution coefficients of valeraldoxime and aldoxime allow:

for valeraldoxime: an equilibrium distribution between the organic and aqueous phases, and it is therefore possible to develop a scheme in which valeraldoxime can be used alone to stabilize plutonium reducing back-extraction of the organic and aqueous phases; while

For aldohexoxime: almost quantitative extraction in the organic phase, it is therefore possible to develop a solution for plutonium reductive stripping in which the aldoxime stabilizes the organic phase with a very small amount of use, in which case the aqueous phase can be stabilized by hydrophilic oximes (such as aldoxime); and is

For both aldoximes: their possible use in the U/Pu allocation step.

1.2-Resistance to nitritation

Pentanaldoxime and hexanaldoxime destroyed nitrous acid (HNO) was evaluated in the following two series of experiments₂) Ability of (c):

a first series for determining the destruction kinetics of valeraldoxime to nitrous acid and, for comparison, butyraldoxime to nitrous acid in an aqueous phase containing 0.1mol/L nitric acid; and

the second series was used to determine the kinetics of destruction of valeraldoxime and hexanaldoxime to nitrous acid and, for comparison, the kinetics of destruction of butyraldehyde oxime to nitrous acid in an organic phase containing 30% (v/v) TBP in n-dodecane.

In the first series of experiments, the initial concentrations of nitrous acid and either valeraldoxime or butyraldehyde oxime in the aqueous nitric acid phase were 0.005mol/L and 0.025mol/L, respectively, in the phase. By spectrophotometry (HNO at λ 370nm)₂Continuous measurement of peaks) to detect the change in the concentration of nitrous acid in these aqueous phases over time.

In the second series of experiments, a first batch of organic phase, previously equilibrated with 1M nitric acid, was first contacted with a volume of aqueous phase containing 1mol/L nitric acid and 0.002mol/L nitrous acid for 10 minutes at ambient temperature (20-25 ℃) with stirring, and then separated from the aqueous phase by centrifugation. Nitrous acid was almost quantitatively extracted in the organic phase.

A second batch of organic phase equilibrated beforehand with 1M nitric acid and added with valeraldoxime, caproaldoxime or butyraldehyde oxime at a concentration of 0.15mol/L in the organic phase was brought into contact with the volume of the aqueous phase containing 1mol/L nitric acid for 10 minutes at ambient temperature (20-25 ℃) with stirring and then separated from this phase by centrifugation. The oxime is separated between the organic and aqueous phases.

The mixture was prepared rapidly from 1mL of the first organic phase (thus containing nitrous acid) and 8mL of the second organic phase. The change in the concentration of nitrous acid in these mixtures was monitored by spectrophotometry (λ ═ 370 nm).

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

In fig. 3, for the first series of experiments, curve a corresponds to the results obtained for valeraldoxime and curve B corresponds to the results obtained for butyraldoxime. The figure also shows the kinetics of destruction of acetaldoxime to nitrous acid (curve C), which has been determined by simulation of experimentally measured rate constants.

In fig. 4, for the second series of tests, curve a corresponds to the results for p-valeraldoxime; curve B corresponds to the results obtained for hexanal oxime; and curve C corresponds to the results obtained for butyraldehyde oxime.

These figures show that:

in aqueous single phase systems, valeraldoxime, although containing a higher number of carbon atoms than butyraldehyde oxime and acetaldoxime, showed comparable resistance to nitritation as butyraldehyde oxime and acetaldoxime (fig. 3); while

In a single-phase organic system in which an organic phase containing valeraldoxime, caproaldoxime or butyraldoxime is brought into pre-contact with an aqueous phase (so that these oximes are separated between the organic and aqueous phases and thus their concentration in the organic phase is reduced), it is observed that: for the same concentration of oxime initially added to the organic phase, the destruction of nitrous acid in the organic phase was significantly accelerated in the presence of either valeraldoxime or caproaldoxime compared to that in the presence of butyraldehyde oxime (fig. 4).

Example 2: stabilization of actinides by pentanal and hexanal oximes

The ability of valeraldoxime and caproaldoxime to stabilize actinides in either aqueous or organic phase was evaluated in the following two series of experiments:

a first series for determining the kinetics of oxidation of uranium (IV) in the presence of valeraldoxime, caproaldoxime and butyraldoxime for comparison and in the absence of any oxime in an organic phase containing 30% (v/v) TBP in n-dodecane, these phases being subsequently separated after the organic phase has been brought into contact with an aqueous phase containing 1.8mol/L nitric acid; and

second series for determining the kinetics of oxidation of uranium (IV) in the presence of valeraldoxime and, for comparison, butyraldoxime, acetaldoxime and hydrazine in an aqueous phase containing 1.3mol/L nitric acid.

In the first series of experiments, the organic phases, equilibrated beforehand with 1.8M nitric acid and, where appropriate, with addition of a concentration of 0.1mol/L oxime, were brought into contact with an aqueous nitric acid phase containing 6g/L uranium (IV) at an O/A volume ratio of 2 for 10 minutes at ambient temperature (20-25 ℃) with stirring. The contacted organic and aqueous phases were separated from each other by centrifugation and the change in the concentration of uranium (IV) in the organic phase was monitored by spectrophotometry (λ 653nm) at 200-hour intervals.

In a second series of experiments, the initial concentrations of uranium (IV) and anti-nitritation agent (oxime or hydrazine) in the aqueous nitric acid phase were 66g/L and 0.2mol/L respectively. The change in the concentration of uranium (IV) in these aqueous phases over time was monitored by spectrophotometry (λ 653nm) at 300 day intervals.

The results of these tests are given in the form of curves in fig. 5 and 6, representing the percentage of residual uranium (IV) as a function of time (in hours in fig. 5, and in days in fig. 6).

In fig. 5, relating to the first series of tests, curve a corresponds to the results obtained for p-valeraldoxime; curve B corresponds to the results obtained for hexanal oxime; curve C corresponds to the results obtained for butyraldehyde oxime, while curve D corresponds to the results obtained in the absence of oxime.

In fig. 6, relating to the second series of tests, curve a corresponds to the results obtained for p-valeraldoxime; curve B corresponds to the results obtained for butyraldehyde oxime; curve C corresponds to the results obtained for acetaldoxime; while curve D corresponds to the results obtained for hydrazine.

As shown in fig. 5, uranium (IV) is fully stabilized in the organic phase in the presence of an oxime for at least 15 hours; and in the absence of any oxime, it completes the oxidation in less than 8 hours. Furthermore, the ability of valeraldoxime and aldohexoxime to stabilize uranium (IV) in the organic phase is greater than the ability of butyraldehyde oxime to stabilize uranium (IV) in the organic phase, since less than 10% of the uranium (IV) is oxidized in 100 hours in the presence of valeraldoxime and aldoxime, which is not the case in the presence of butyraldehyde oxime.

In the aqueous phase, the valeraldoxime also stabilized uranium (IV) more than the butyraldehyde oxime. However, valeraldoxime stabilized uranium (IV) less than acetaldoxime and hydrazine stabilized uranium (IV) (fig. 6).

All these time periods in days are still much longer than the time during which the organic and aqueous phases are present in plutonium industrial stripping operations.

These results show that aqueous nitric acid phases containing high concentrations of uranium (IV) can be stabilized with the monoxime protocol of valeraldoxime or with the dioxime protocol used with acetaldoxime (e.g. with hexaaldoxime in the organic phase), thus avoiding the use of hydrazine.

Example 3: anti-nitritation properties of valeraldoxime and caproaldoxime under chemical conditions representative of plutonium reducing stripping operations

The resistance to nitritation of valeraldoxime and hexanaldoxime was evaluated in the following series of tests (denoted BX1 to BX10) representing the chemical conditions under which the plutonium reducing back-extraction was carried out in the PUREX process, involving:

reducing plutonium (IV) to plutonium (III) with uranium (IV), and reducing plutonium (III) to plutonium (IV) with nitrous acid;

destruction of nitrous acid by one of the above oximes; and

distribution of the substance of interest between the aqueous phase and the organic phase.

For this purpose, the following substances were used:

as aqueous phase: a solution with 1 or 2mol/L nitric acid, containing uranium (VI), uranium (IV) (as plutonium (IV) reducing agent) and optionally hydrazine and technetium in the concentrations indicated in tables 3 and 4 below; and

as an organic phase: a 30% (v/v) solution of TBP in HTP, containing oxime, uranium (VI) and plutonium (IV) at the concentrations indicated in tables 3 and 4 below.

The oxime was added to the organic phase as a solid (the amount of oxime added was controlled by weighing).

The organic and aqueous phases were contacted at ambient temperature (20-25 ℃) with stirring for 15 minutes with an O/a volume ratio of 2 (except for test BX3 where the contact time was only 5 minutes) after which the phases were separated from each other.

After this separation, the concentrations of uranium (VI), uranium (IV) and plutonium (III) in the aqueous phase were measured by ultraviolet-visible spectroscopy, and the total concentration of plutonium in the aqueous phase was measured by α -spectrophotometry. The concentrations of uranium (VI) and uranium (IV) in the organic phase were measured by ultraviolet-visible spectrophotometry, and the total concentration of plutonium in the organic phase was measured by alpha-spectrophotometry.

Based on the results of these measurements, for each testDetermination of the ratio between the consumption of uranium (IV) and the quantity of plutonium stripped (expressed as U (IV))_{Consumption of}/Pu_{Back extraction}) And the separation factor of plutonium (denoted as FD)_Pu)。

The results of these tests are given in tables 3 and 4 below, table 3 corresponding to the results obtained for the tests carried out with hexaaldoxime (BX1 to BX5, BX8 and BX10), while table 4 corresponds to the results obtained for the tests carried out with valeraldoxime (BX6 and BX 7).

TABLE 3

TABLE 4

As shown in these tables:

when the concentration of the aldohexoxime in the organic phase is 0.1mol/L and the initial weight ratio (U (IV)/Pu) is 0.8 to 1.5, the consumption of uranium (IV) and the stripping amount of plutonium (ratio U (IV))_{Consumption of}/Pu_{Back extraction}) Between 0.5 and 0.6; the parasitic phenomenon of plutonium reoxidation is also very low, even non-existent; these results were observed for aqueous phases with nitric acid concentrations of 1mol/L or 2mol/L (tests BX1 to BX 5);

the reduction in the concentration of aldohexoxime in the organic phase by half (0.05mol/L vs. 0.1mol/L) and the presence of technetium in the aqueous phase leads to a higher consumption of uranium (IV) (ratio U (IV)_{Consumption of}/Pu_{Back extraction}1), but it remains moderate (test BX8 and test BX 10);

valeraldoxime can also be limited to cause extraThe redox phenomena of uranium (IV) are consumed, but the performance is lower compared to that of hexanal oxime, since the ratio U (IV) obtained with valeral oxime_{Consumption of}/Pu_{Back extraction}Between 0.6 and 0.8 (tests BX8 and BX 10).

The concentration change in the organic phase of the uranium (IV) obtained after the tests BX5, BX10 and BX6 was monitored by spectrophotometry (λ 653nm) at intervals of several hours.

The results of this monitoring are shown in fig. 7, 8 and 9, corresponding to organic phases BX5, BX10 and BX6, respectively.

These figures demonstrate that valeraldoxime and caproaldoxime are capable of stabilizing uranium (IV) in the organic phase. This stabilization is less in the presence of technetium, but the kinetics of oxidation of uranium (IV) are relatively slow, since the uranium (IV) concentration is reduced by half in 50 minutes.

Example 4: development of a spent fuel solution treatment protocol including a U/Pu distribution step without hydrazine

A treatment protocol was developed for spent fuel dissolving solutions, comprising a U/Pu partitioning step carried out in the absence of hydrazine, but using a hexanaldoxime/acetaldoxime association as anti-nitritation system, hexanaldoxime for the organic phase and acetaldoxime for the aqueous phase.

Before the development of this scheme, it has been demonstrated that:

first, in the presence of technetium, aldoxime does replace hydrazine as an anti-nitrous acidifying agent in the aqueous phase; and is

Secondly, hexanal oxime also stabilizes the uranium (IV) in the organic phase for carrying out the so-called "Np scrubbing" operation, the objective of which in the PUREX and COEX processes is to remove from the aqueous solution the neptunium resulting from the plutonium stripping operation (which has been stripped during this operation).

4.1-anti-nitritation Properties of acetaldoxime in the Presence of technetium in aqueous phase

An experiment was performed to compare the resistance to nitritation of acetaldoxime in the aqueous phase with that of hydrazine in the presence of technetium.

For these tests, the following protocol was applied:

preparing aqueous solutions containing 9g/L of uranium (IV) and 2mol/L of nitric acid and 0.2mol/L of acetaldoxime or hydrazine, these solutions being thermostatically controlled at 35 ℃;

to these solutions, an aqueous solution containing 8.88g/L (i.e., 0.09mol/L) technetium (VII) is added to achieve a final technetium concentration of 100mg/L or 200 mg/L; and after stirring

The kinetics of oxidation of uranium (IV) in the aqueous solution was monitored by spectrophotometry (λ ═ 653nm) over a period of 100 minutes.

The results of these tests are given in FIG. 10, wherein the results in the presence of Tc of 100mg/L and 200mg/L for acetaldoxime correspond to the symbols ■ and X, respectively, and the results in the presence of Tc of 100mg/L and 200mg/L for hydrazine correspond to the symbols a and ●, respectively.

As shown in the figure, the anti-nitritation properties of aldoxime in the presence of 100mg or 200mg technetium in aqueous phase are comparable to hydrazine.

Thus, acetaldehyde oxime may be used as an anti-nitrous acidifier in place of hydrazine.

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

The following two experiments (denoted BS16 and BS17) were performed, using:

as an organic phase: a solution of 30% (v/v) TBP in HTP, with or without 0.1mol/L aldohexoxime; and

as aqueous phase: an aqueous solution with 1.3mol/L nitric acid containing uranium (IV), acetaldoxime, plutonium (III) and technetium in the concentrations indicated in table 5 below; technetium is added to the aqueous phase as a concentrated tc (vii) solution of 8.88g/L before they are contacted with the organic phase.

The organic phase and the aqueous phase are brought into contact volumetrically for 15 minutes at ambient temperature (20-25 ℃) with stirring and the phases are then separated from one another.

The concentration of uranium (IV) in the aqueous and organic phases was measured and the percentage of uranium (IV) consumed in each trial was determined (expressed as U (IV))_{Consumption of})。

The results are shown in Table 5 below.

This shows that the presence of aldohexoxime (trial BS16) in the organic phase enables the consumption of uranium (IV) to be reduced by 50% compared to the consumption without the oxime (trial BS 17).

TABLE 5

4.3 treatment protocol

Figure 11 shows a treatment scheme for a spent fuel dissolving solution developed.

In this scheme, two main steps of the first purification cycle of the COEX process are found, namely:

(1) a step of purifying the uranium and the plutonium and a certain number of fission products of actinides (III) (americium and curium), which comprises:

an operation called "U/Pu co-extraction" in fig. 11, for co-extracting uranium in oxidation state VI, plutonium in oxidation state IV and neptunium in oxidation state VI from the dissolution liquor by means of an organic phase containing 30% (v/v) TBP in HTP;

an operation called "FP scrubbing" in FIG. 11 for removing fission products from the organic phase resulting from the "U/Pu Co-extraction" operation, in particular ruthenium and zirconium extracted in the "U/Pu Co-extraction";

an operation called "Tc wash" in FIG. 11 for removing technetium extracted in the "U/Pu co-extraction" from the organic phase resulting from the "FP wash" by the aqueous phase; and

an operation called "extra U/Pu co-extraction" in fig. 11, for recovering fractions of uranium (VI), plutonium (IV) and neptunium in the organic phase, followed by recovery of technetium in the "technetium-washed" aqueous phase; and

(2) a step of splitting uranium and plutonium into two aqueous streams, one containing uranium and the other containing plutonium and uranium (U/Pu weight ratio of about 20:80 to 30:70) and comprising:

an operation called "Pu/U stripping" in fig. 11, for stripping plutonium and a portion of the uranium contained in the organic phase resulting from "Tc scrubbing", carried out by means of an aqueous phase containing uranium (IV) as reducing agent capable of reducing plutonium to oxidation state III;

an operation called "Np scrubbing" in fig. 11, for removing uranium from the aqueous phase resulting from the "Pu/U stripping", which is in excess with respect to the expected weight ratio U/Pu from 20:80 to 30:70, and subsequently removing the neptunium fraction from the aqueous phase of the "Pu/U stripping"; and

an operation called "U-strip" for stripping the uranium and neptunium from the organic phase resulting from the "Pu/U-strip" by means of an aqueous phase.

However, in the scheme shown in FIG. 11, the anti-nitrosating agent (i.e., hydrazine) used in the COEX process is replaced by a hexaaldoxime/acetaldoxime combination.

As shown in fig. 11, in view of its strong lipophilicity, hexanaldoxime (designated HexOx in fig. 11) was added to the organic phase entering the extractor 5 where "Np wash" occurred, and to the organic phase resulting from "Tc wash" before entering the extractor 6.

In view of its hydrophilic properties, acetaldoxime (denoted AcOx in fig. 11) is added to the aqueous phase circulating in the extractor 6 in three different stages of the extractor: stage 8, in which the acetaldoxime is injected into the aqueous phase for stripping; and stages 1 and 4 in which acetaldoxime is injected into the aqueous stream used to supply uranium (IV) to the aqueous phase.

Basic acquisitions regarding oximes used in both the aqueous and organic phases were used to develop an initial model to be able to model the separation between the aqueous and organic phases used in the process, as well as their reaction kinetics with nitrous acid. These models are implemented in PAREX code, i.e., software is able to simulate the partitioning of target substances in operations, such as uranium and plutonium into two aqueous streams. On the basis of this simulation, the operating parameters were determined for the experimental tests of the scheme shown in fig. 11.

Fig. 12 compares the concentration profiles of uranium (IV) in the aqueous phases recycled in

extractors

5 and 6, for example calculated firstly for the scheme shown in fig. 11 (curve a) and secondly for a similar scheme using hydrazine (curve B). The ideal distribution curve (curve C) obtained by the reoxidation reaction of the neutralized plutonium (III) (in PAREX coding) is also shown.

As shown in the figure, the use of the hexanal oxime/acetaldoxime combination allows the uranium (IV) profile to be more concentrated than that obtained with hydrazine, thus confirming the reduced uranium (IV) consumption in the presence of these oximes.

The scheme shown in fig. 11 was successfully implemented on an alarante screened cell production line, a true spent fuel solution. This solution enables the production of a plutonium stream with a concentration of 10g/L, in highly concentrated uranium (IV) (16g/L) and without any uranium (IV) additive in the "Np scrubbing" operation, which is necessary in similar solutions using hydrazine. The consumption of uranium (IV) is also lower than with the hydrazine solution.

Fig. 13 shows the concentration profiles of plutonium in the aqueous phase circulating in

extractors

5 and 6, as obtained by experiment (symbol x) and by PAREX coding (curve-), while fig. 14 shows the concentration profiles of uranium (IV), uranium (VI) and total uranium in the aqueous phase circulating in these same extractors, as obtained by experiment and calculation; in the figure, symbols x, diamond-solid, and ■ correspond to concentration profiles of experimentally obtained uranium (IV), uranium (VI), and total uranium, respectively, and curves A, B and C correspond to concentration profiles of uranium (IV), uranium (VI), and total uranium, respectively, obtained by calculation.

In addition, table 6 below gives: the concentration of uranium in the aqueous phase produced by extractor 5 (expressed as [ U (IV))]_{Pu producing stream}) The concentration of plutonium in the aqueous phase produced in extractor 5 (expressed as [ Pu ]]_{Pu producing stream}) The ratio between the flow of uranium (IV) entering an extractor 6 and the flow of Pu entering this same extractor (expressed as U (IV)/Pu_{Enter into}) Percentage of uranium (IV) consumed (expressed as U (IV))_{Consumption of}) And the ratio between the consumption of uranium and the plutonium ingress (denoted U (IV))_{Consumption of}/Pu)。

For comparison, the table gives these same concentrations, ratios and percentages as obtained experimentally using a similar protocol for hydrazine.

TABLE 6

Cited references

[1]WO-A-2006/072729

[2]WO-A-2011/000844

[3]WO-A-2008/148863

Claims

1. Use of at least one aldoxime of formula R-CH ═ N-OH, wherein R is a linear or branched hydrocarbon chain having at least 4 carbon atoms, as an anti-nitrous acidifier in a plutonium reducing stripping operation, wherein said plutonium reducing stripping operation comprises:

contacting an organic non-water-miscible phase comprising an extractant and plutonium in 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, the reducing agent being selected from uranium (IV), hydroxylamine nitrate, alkylated derivatives of hydroxylamine, ferrous sulphamate and sulphamic acid, and one of the organic and aqueous phases further comprising the aldoxime; then the

The organic and aqueous phases thus contacted are separated.

2. The use according to claim 1, wherein R is a linear or branched hydrocarbon chain having 4 to 12 carbon atoms.

3. The use according to claim 2, wherein R is a linear or branched hydrocarbon chain having 4 to 8 carbon atoms.

4. Use according to claim 3, wherein R is a linear alkyl chain having from 4 to 8 carbon atoms.

5. Use according to claim 4, wherein the aldoxime is valeraldoxime or caproaldoxime.

6. Use according to claim 1, wherein the reducing agent is uranium (IV) or hydroxylamine nitrate.

7. Use according to claim 1, wherein the extractant is tri-n-alkyl phosphate.

8. Use according to claim 7, wherein the extractant is tri-n-butyl phosphate.

9. The use according to claim 1, wherein the aldoxime is used in a concentration of 0.01 to 3mol/L in the organic or aqueous phase.

10. Use according to claim 1, wherein the aqueous phase further comprises an oxime which is not extractable by the organic phase.

11. Use according to claim 10, wherein the oxime not extractable by the organic phase is acetaldoxime.

12. Use according to claim 1, in which the plutonium reducing stripping operation is one of plutonium stripping operations of the PUREX process or of the COEX process.