JP2018536847A - Use of an aldoxime containing at least 5 carbon atoms as an anti-nitrite agent in an operation for reductive stripping of plutonium - Google Patents

Abstract

The present invention relates to the use of an aldoxime containing at least 5 carbon atoms as an anti-nitrite agent in a plutonium reduction stripping operation. The present invention is implemented in any method for the treatment of spent nuclear fuel, including one or more operations for the reduction stripping of plutonium, and in particular in modern factories for the treatment of spent nuclear fuel. It can be applied in such PUREX methods and in methods derived therefrom.

Description

  The present invention relates to the field related to the processing of spent nuclear fuel.

  More specifically, the present invention relates to the use of aldoximes having at least 5 carbon atoms as anti-nitrite agents in plutonium reductive stripping operations.

  The present invention may be applied to any method for the treatment of spent nuclear fuel including one or more reduction stripping operations of plutonium.

  In particular, in the PUREX process carried out, for example, in the latest nuclear fuel processing plants (ie the UP3 and UP2-800 plants in La Hague, France, and the Rokkasho Village plant in Japan) First, to carry out the U / Pu distribution step of the first decontamination cycle of the method, and secondly, the plutonium purification cycle commonly referred to as the “second plutonium cycle” following this first decontamination cycle In order to improve the plutonium decontamination of fission products.

  They are also described in several methods derived from this Purex method, such as those described in the international patent application known under the name of the COEX method [Patent Document 1], or in the international patent application [Patent Document 2]. It is also included.

  In the plutonium reduction stripping operation carried out in the above method for the treatment of spent nuclear fuel, the plutonium is taken from the organic phase (or solvent phase) in which the plutonium is in the oxidation state (IV), It is passed to the aqueous phase by reducing it to oxidation state III, which has a very low affinity for the organic phase.

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

  For example, in the first decontamination cycle of the Purex process (referred to more simply as the “PUREX process” in the rest of the specification) performed at a modern nuclear fuel reprocessing plant, the U / Pu distribution process The reducing agent used for stripping plutonium in uranium is uranium (IV) (or uranas nitrate), while the anti-nitrite is hydrazinium nitrate, also known as hydrazine.

The main chemical reactions to be considered are:
-Reduction of plutonium (IV) to plutonium (III) with uranium (IV) (functional reaction):
U ⁴⁺ + 2Pu ⁴⁺ + 2H ₂ O → UO ₂ ²⁺ + 2Pu ³⁺ + 4H ⁺
-Reoxidation of plutonium (III) to plutonium (IV) (parasitic reaction):
Pu ³⁺ + HNO ₂ + 1.5H ⁺ + 0.5NO ₃ ⁻ → Pu ⁴⁺ + 0.5H ₂ O + 1.5HNO ₂
-Degradation of nitrous acid to azohydric acid with hydrazine (useful reaction):
N ₂ H ₅ NO ₃ + HNO ₂ → N ₃ H + HNO ₃ + 2H ₂ O.

  The first two reactions occur in the aqueous and organic phases, whereas the destruction of nitrous acid by hydrazine occurs only in the aqueous phase due to the non-extractability of hydrazine by the organic phase, Consists of 30% (v / v) tri-n-butyl phosphate (or TBP) in hydrogenated tetrapropylene (or HTP).

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

  When an experimental study was conducted with a laboratory centrifugal extractor, it was confirmed that the consumption of uranium (IV) due to oxidation was very high even when the residence time of the extractor was short (about several seconds). This oxidation of uranium (IV) occurs essentially in the organic phase because hydrazine is contained only in the aqueous phase. As a result, the plutonium reduction stripping scheme provides a large excess of reducing agent.

Hydroazide produced by the destruction of nitrous acid with hydrazine is then reacted:
HN ₃ + HNO ₂ → N ₂ + N ₂ O + H ₂ O
Reacts with nitrous acid according to

  However, the kinetics of this reaction is much slower than the destruction of nitrous acid by hydrazine, which means that hydrazoic acid is found in the effluent aqueous and organic phases of the U / Pu partitioning process.

  Therefore, since hydrazine is non-extractable by the organic phase and therefore acts only in the aqueous phase, this leads to high reagent consumption and the production of chemical species that hinder the industrial application of this method. .

  In order to solve this problem, in the international patent application [Patent Document 3], butanal oxime, also called butyraldehyde oxime or butyl aldoxime, is combined with hydrazine, so that butanal oxime can stabilize the organic phase. However, it has been proposed to use a two-phase anti-nitrite system in which hydrazine stabilizes the aqueous phase.

The use of butanal oxime with hydrazine has been particularly associated with the ability to significantly reduce the amount of uranas nitrate and hydrazine required to carry out reductive stripping of plutonium, and thereby the non-extraction of hydrazine in the organic phase. It allows several advantages of reducing the disadvantages, however it is not completely sufficient for the following reasons:
-The relatively low extraction of butanal oxime by the organic phase forced the addition of a large amount of this oxime into the extractor in which plutonium reductive stripping occurred, resulting in an effective concentration of butanal oxime in the organic phase When it is desired to obtain; especially in the U / Pu partitioning process, the extraction of butanal oxime with the organic phase is greatly reduced by saturation of this phase with the actinide, which ultimately reduces the use of this oxime, Make it almost unsuitable for carrying out this distribution process;
-The continuous use of hydrazine in the aqueous phase; in fact, despite the fact that hydrazine is one of the most effective anti-nitrites in the aqueous phase, its use is Not only is it caused by the problems already shown in connection with production, but also is limited by the reasons for its toxicity: hydrazine is virtually on the list of CMR substances, ie chemical registration, evaluation, The European Parliament and Council Regulation (EC) 1907/2006 on Authorization and Restriction (REACH Regulation) has or is potentially carcinogenic, mutagenic, and / or reproductive and developmental toxic And sooner or later will be included in the list of substances subject to authorization under Annex XIV of this Regulation, in which case the European Chemicals Agency (Eu Unless specific exemption indicated by opean Chemicals Agency (ECHA)), its marketing and industrial use will be banned.

  In addition, a reaction of butanal oxime with hydrazine has been observed leading to the formation of hydrazone. This reaction reduces the performance of butanal oxime, resulting in overconsumption of these two reagents.

  In view of the above, we are therefore compounds with high antinitrite activity, but their use is due to the use of hydrazine as currently used in the PUREX process or [Patent Document Attempts were made to find the compound without the disadvantages caused by the use of a two-phase butanal oxime / hydrazine system as proposed in 3].

  More specifically, we have found that these compounds are saturated with an actinide by the organic phase, particularly the type of organic phase used in the PUREX process (under the same temperature and pressure conditions). Must be more extractable than butanal oxime, thereby (1) reducing the amount of these compounds required for reductive stripping of plutonium, and (2) the PUREX process. We set our own goal of enabling it for plutonium stripping in the U / Pu distribution process in the first decontamination cycle of the process, and for plutonium stripping in the second plutonium cycle of the process.

  We further set our own goal that these compounds must be made to completely avoid the use of hydrazine.

International Publication No. 2006/072729 International Publication No. 2011/000844 International Publication No. 2008/148863

  These and other purposes are as anti-nitrite agents in plutonium reductive stripping operations, at least one aldoxime having at least 5 carbon atoms, ie the formula R—CH═N—OH, wherein R Is a hydrocarbon chain having at least 4 carbon atoms] and is achieved by the present invention, which proposes the use of oximes.

  Preferably, the aldoxime satisfies the above formula, wherein R contains at most 12 carbon atoms, and advantageously at most 8 carbon atoms.

  Even better, the aldoxime satisfies the above formula where R is a straight chain alkyl chain having 4 to 8 carbon atoms.

The aldoxime is of the formula _{n-C 4 H 9 -CH =} N-OH, valeraldehyde oxime or barrel aldoxime also referred pentanal oxime, hexanal oxime of the formula _{n-C 5 H 11 -CH =} N-OH , hepta oxime of the formula _{n-C 6 H 13 -CH =} n-OH, octa oxime of the formula _{n-C 7 H 15 -CH =} n-OH, and wherein _{n-C 8 H 17 -CH =} N- It is a nonanal oxime of OH.

  Among the aldoximes, special preference is given to pentanal oxime and hexanal oxime.

In accordance with the present invention, the plutonium reduction stripping operation is preferably:
Contacting the non-water miscible organic phase comprising an extractant and oxidation state IV plutonium in an organic diluent with an aqueous phase comprising nitric acid and a reducing agent capable of reducing plutonium (IV) to plutonium (III). Wherein aldoxime is contained either in the organic phase or in the aqueous phase, depending on its solubility in water; then-separating the organic and aqueous phases so contacted The process of
including.

  Therefore, it is partially soluble in water and partially soluble in organic diluents that can be used in plutonium reduction stripping operations (under conditions of temperature and pressure normally used in these operations). ) Pentanal oxime can be added to either the aqueous phase or the organic phase, while aldoximes with 6 or more carbon atoms that are insoluble or nearly insoluble in water (under the above conditions) are added to the organic phase Is done.

  In the present invention, the reducing agent contained in the aqueous phase is preferably uranium (IV), hydroxylammonium nitrate, also called hydroxylamine nitrate, alkylated derivatives of hydroxylamine, ferrous sulfamate, and sulfamine. Selected from among acids.

  Among these reducing agents, particular preference is given to uranium (IV) and hydroxylammonium nitrate, which in the PUREX process, first in the U / Pu distribution step in the first decontamination cycle, Next, in the second plutonium cycle are the two agents used to reduce plutonium (IV) to plutonium (III).

  Also, the extractant is preferably tri-n-alkyl phosphate and better TBP, while the organic diluent is preferably linear or branched dodecane, such as n-dodecane or HTP, isoparaffinic solvents, For example, Isane IP185, Isan IP165, or Isopar L, or kerosene, in which case the extractant is preferably contained in the organic diluent at a rate of 30% (v / v) .

  In any case, the aldoxime is preferably used at a concentration of the organic or aqueous phase ranging from 0.01 mol / L to 3 mol / L, and better from 0.05 mol / L to 0.5 mol / L, On the other hand, the reducing agent is preferably used at concentrations in the aqueous phase ranging from 0.02 mol / L to 0.6 mol / L, and better from 0.2 mol / L to 0.4 mol / L.

  For nitric acid, this is advantageously contained in the aqueous phase at concentrations ranging from 0.05 mol / L to 2 mol / L.

  In the present invention, aldoxime is used as the only anti-nitrite agent in the plutonium reductive stripping operation when the organic and aqueous phases are in contact with each other and are balanced between them. Is possible. However, if this is not the case, aldoximes are highly extractable in the organic phase (under conditions of temperature and pressure normally used in plutonium reductive stripping operations)-this is typically hexanal oxime Or occurs for aldoximes having 6 or more carbon atoms, such as octanal oximes, where the aldoximes are advantageously non-extractable (under the same temperature and pressure conditions) oximes by this organic phase. Used in combination with two anti-nitrite agents.

In this case, the non-extractable oxime contained in the aqueous phase is preferably formaldoxime, also referred to as formaldehyde oxime, having the formula CH ₂ ═N—OH, or the formula CH ₃ —CH═N—OH. Acetaldehyde oxime, also referred to as acetaldehyde oxime, and advantageously aqueous in the range of 0.01 mol / L to 1 mol / L, and better 0.05 mol / L to 0.2 mol / L Used in phase concentration.

  According to one particular preferred provision of the invention, the plutonium reduction stripping operation is preferably one of the plutonium stripping operations in the PUREX or COEX process.

  The present invention allows for a number of advantages. It is derived from plutonium (III) in both the aqueous and organic phases when used alone for some and when used in combination with non-extractable oximes by the organic phase for others. Provides an amount of anti-nitrite that can most effectively prevent reoxidation to plutonium (IV).

  Therefore, whether the present invention is for an operation as performed in the U / Pu distribution process of the PUREX process, or for an operation as performed in the second plutonium cycle of this same process. In addition to the fact that it allows the reduction stripping operation of plutonium without the use of hydrazine, it also performs these operations compared to the amount required when the anti-nitrite is hydrazine. It also allows a very powerful reduction in the amount of reducing agent and anti-nitrite needed for the process.

  The present invention therefore contemplates a reduction in the number of points required to add these anti-nitrites to equipment specialized for plutonium reduction stripping operations, and therefore simplification of this equipment. Make it possible.

  Furthermore, plutonium stripping is more efficient, and at the end of the stripping operation leads to an aqueous phase having a higher plutonium concentration than that obtained when using hydrazine as an anti-nitrite agent. In view of this, the present invention also makes it possible to envisage reducing the size of the equipment currently used to carry out the reduction stripping operation of plutonium.

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

  Obviously, these examples are merely given as illustrative of the subject matter of the present invention and are not limiting in any way.

FIG. 7 shows the partition coefficients of pentanal oxime (symbol ■) and hexanal oxime (symbol ●) between an organic phase containing TBP in n-dodecane and an aqueous phase containing different concentrations of nitric acid; Therefore, this figure also shows the partition coefficient (symbol ▲) obtained under the same conditions for butanal oxime. FIG. 5 shows the distribution coefficient of pentanal oxime (symbol ■) and hexanal oxime (symbol ●) between the organic phase and the aqueous phase, in terms of the concentration of uranium (IV) and the concentration of nitric acid. Simulate the organic and aqueous phases obtained in the U / Pu distribution step of the process. FIG. 5 shows the distribution coefficient of pentanal oxime (symbol ■) and hexanal oxime (symbol ●) between the organic phase and the aqueous phase, in terms of the concentration of uranium (IV) and the concentration of nitric acid. Simulate the organic and aqueous phases obtained in the U / Pu distribution step of the process. FIG. 3 illustrates the kinetics of nitrite destruction by pentanal oxime in an aqueous nitric phase (curve A); for comparison, this figure also shows that by butanal oxime (curve B, as obtained under the same conditions). ), And acetoaldoxime (curve C), also illustrating the kinetics of nitrite destruction. FIG. 3 illustrates the kinetics of nitrite destruction by pentanal oxime (curve A) and by hexanal oxime (curve B) in an organic phase containing TBP in n-dodecane; Also illustrated is the kinetics of destruction of nitrite by (but curve C) butanal oxime, as obtained under the same conditions. In an organic phase containing TBP in n-dodecane, the pentanal oxime (curve A) and hexanal oxime (curve B) after contacting these organic phases with an aqueous nitric acid phase and subsequently separating the phases. FIG. 4 illustrates the oxidation kinetics of uranium (IV) obtained in the presence; for comparison, this figure also shows the presence of butanal oxime (curve C) and in the absence of any oxime (curve D). Also illustrated is the oxidation kinetics of uranium (IV) as obtained under the same conditions. FIG. 1 illustrates the oxidation kinetics of uranium (IV) obtained in the presence of pentanal oxime in an aqueous nitric acid phase (curve A); for comparison, this figure also shows butanal oxime (curve B), acetoald Also illustrated is the oxidation kinetics of uranium (IV) as obtained in the presence of oxime (curve C) and hydrazine (curve D). It is a figure which illustrates the oxidation kinetics of the uranium (IV) contained in the organic phase (TBP / HTP) after the reduction stripping test of plutonium when hexanal oxime is used as an anti-nitrite agent. Uranium contained in the organic phase (TBP / HTP) after reduction stripping test of plutonium when hexanal oxime is used as anti-nitrite and technetium is stripped with plutonium It is a figure which illustrates the oxidation kinetics of IV). FIG. 4 illustrates the kinetics of oxidation of uranium (IV) in the organic phase (TBP / HTP) after a plutonium reduction strip test when pentanal oxime is used as an anti-nitrite agent. FIG. 3 illustrates the oxidation kinetics of uranium (IV) in the presence of acetaldoxime in an aqueous nitric acid phase containing 100 mg / L (symbols ■) or 200 mg / L (symbols x) technetium; The figure also illustrates the oxidation kinetics of uranium (IV) as obtained in the presence of hydrazine and 100 mg / L (symbol ▲) or 200 mg / L (symbol ●) technetium under the same conditions. FIG. 1 shows a scheme for treating spent nuclear fuel lysate, including a U / Pu distribution step, in which the hexanal oxime / acetoaldoxime combination is used as an anti-nitrite system; Rectangles 1 to 7 represent multi-stage extractors (mixer settlers, pulse columns, centrifugal extractors) as commonly used for processing spent nuclear fuel; and the organic phase entering and exiting the extractor is The aqueous phase that is symbolized by a solid line while entering and exiting the extractor is symbolized by a dotted line. FIG. 12 illustrates a profile of uranium (IV) concentration in the aqueous phase circulating in the extractors 5 and 6 of the scheme illustrated in FIG. 11, as obtained by computer calculation (curve A); for comparison In this scheme, the uranium (IV) concentration profile obtained when hexanal oxime and acetoaldoxime are replaced by hydrazine (curve B), and when the reoxidation reaction of plutonium (III) is completely neutralized The resulting uranium (IV) concentration profile (curve C) is also shown. Diagram illustrating the profile of plutonium concentration in the aqueous phase circulating in the extractors 5 and 6 of the scheme illustrated in FIG. 11, as obtained experimentally (symbol x) and by computer calculation (curve-). It is. Profiles of uranium (IV), uranium (VI), and total uranium concentrations in the aqueous phase circulating in the extractors 5 and 6 of the scheme illustrated in FIG. 11, as obtained experimentally and by computer calculations In this figure, the symbols x, ◆, and ■ correspond to experimentally obtained uranium (VI), uranium (IV), and total uranium concentration profiles, respectively, while curve A , B, and C correspond to uranium (VI), uranium (IV), and total uranium concentration profiles obtained by computer calculation, respectively.

Example 1: Properties of pentanal oxime and hexanal oxime 1.1-Partition coefficient The partition coefficient represented by D for pentanal oxime and hexanal oxime is two series of tests:
-Measuring these partition coefficients between an organic phase containing 30% (v / v) TBP in n-dodecane and an aqueous phase containing from 0.2 mol / L to 2 mol / L of nitric acid. A second series intended to measure these partition coefficients between the organic phase and the aqueous phase, which are uranium (IV) and nitric acid concentrations From the point of view, the organic and aqueous phases obtained in the U / Pu distribution process of the PUREX process are simulated, and this series is carried out in a mixer-settler unit having 8 stages represented by BX1 to BX8.
It measured using.

  For these two series of tests, each organic phase was contacted in volume / volume with the aqueous nitric acid phase at room temperature (20-25 ° C.) and under stirring for 15 minutes. Pentanal oxime was added to the aqueous phase, while hexanal oxime was added to the organic phase at a concentration of 0.1 mol / L each.

  The contacted organic and aqueous phases are separated from each other by centrifugation and the concentration of aldoxime in these phases is determined by high performance liquid chromatography (HPLC) for the aqueous phase and gas phase chromatography (GPC for the organic phase). ).

  The distribution coefficients obtained in the first series of series are shown in Table 1 below. They are also shown in FIG. 1 where the values shown in this table have been transferred, and in this, the partition coefficient of pentanal oxime is represented by the symbol ■, whereas that of hexanal oxime The distribution coefficient is represented by the symbol ●. For comparison, FIG. 1 also shows the partition coefficient (▲) obtained for butanal oxime under the same conditions.

  The partition coefficients obtained in the second series of tests are shown in Table 2 below. They are also shown in FIGS. 2A and 2B, where the partition coefficient (Y-axis) and aqueous phase acidity (X-axis) values have been transferred, where the partition coefficient (Y− Axis) and acidity of the aqueous phase (X-axis) have been transferred, and in this, the partition coefficient of pentanal oxime corresponds to the symbol ■, while the partition coefficient of hexanal oxime corresponds to the symbol ● Equivalent to. The ordinate is decimal in FIG. 2A and logarithmic scale in FIG. 2B.

  As shown in Table 1 and FIG. 1, pentanal oxime and hexanal oxime show significantly higher partition coefficients than those of butanal oxime, which are much more extractable than butanal oxime in the organic phase. It means that there is.

  When the aqueous phase contains actinides (Table 2 and FIGS. 2A and 2B), the partition coefficients of pentanal oxime and hexanal oxime are reduced compared to their values in the absence of actinide; however, they are sufficiently high Until now, ensure that pentanal oxime and hexanal oxime are still fully extracted. Under the same conditions, the partition coefficient of butanal oxime is less than one.

The partition coefficient of pentanal oxime and hexanal oxime enables:
-For pentanal oxime: Due to the balanced distribution between the organic and aqueous phases, it is also possible for pentanal oxime alone to stabilize both the organic and aqueous phases. The possibility of developing schemes for reducing stripping operations;
-For hexanal oxime: Due to the nearly quantitative extraction in the organic phase, because of the reduction stripping operation of plutonium, where hexanal oxime can also be used in very small amounts to stabilize the organic phase. In which case the aqueous phase can be stabilized by a hydrophilic oxime such as acetoaldoxime; and -for these two aldoximes: their in the U / Pu partition step Possible use.

1.2 the ability to destroy nitrite to (HNO ₂₎ anti-nitrous action pentanal oxime and hexanal oxime, 2 series of tests, namely:
-The first series intended to measure the kinetics of nitrous acid destruction by pentanal oxime, and for comparison, the kinetics of nitrous acid destruction by butanal oxime in an aqueous phase containing 0.1 mol / L nitric acid. Nitrite destruction kinetics by pentanal oxime and by hexanal oxime and nitrous acid destruction kinetics by butanal oxime for comparison with 30% (v / v) TBP in n-dodecane; A second series intended to be measured in the organic phase containing,
Evaluated.

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

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

  A second batch of organic phase, pre-equilibrated with 1M nitric acid and to which pentanal oxime, hexanal oxime, or butanal oxime was added at a concentration of 0.15 mol / L organic phase, in volume / volume The aqueous phase containing 1 mol / L nitric acid was contacted for 10 minutes at room temperature (20-25 ° C.) and under stirring and then separated from this phase by centrifugation. The oxime partitioned itself between the organic and aqueous phases.

  A mixture quickly formed between 1 mL of the organic phase obtained from the first batch (and hence containing nitrous acid) and 8 mL of the organic phase obtained from the second batch. Changes in nitrous acid concentration in these mixtures were monitored by spectrophotometric analysis (λ = 370 nm).

  The results of these tests are shown in FIGS. 3 and 4 in the form of a curve representing the percentage of residual nitrous acid as a function of time (seconds in FIG. 3 and minutes in FIG. 4).

  In FIG. 3, in relation 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 breakdown kinetics of nitrous acid by acetoaldoxime (curve C), which was determined by simulation from experimentally measured rate constants.

  In FIG. 4, in connection with 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 is Corresponds to the results obtained for butanal oxime.

These figures are:
-In aqueous single-phase systems, pentanal oxime has the same anti-nitrite effect as butanal oxime and acetoaldoxime, despite containing more carbon atoms than butanal oxime and acetoaldoxime (FIG. 3); On the other hand, in an organic single-phase system, the organic phase containing pentanal oxime, hexanal oxime, or butanal oxime is previously contacted with the aqueous phase (between the organic phase and the aqueous phase). For those same concentrations of oxime initially added to the organic phase, the concentration of nitrous acid in the organic phase is reduced. When destruction is in the presence of pentanal oxime or hexanal oxime, compared to that in the presence of butanal oxime, Is the fact that the observed accelerated Laka (FIG. 4),
Is shown.

Example 2: Stabilization of actinides with pentanal oxime and hexanal oxime The ability of pentanal oxime and hexanal oxime to stabilize actinides in an aqueous or organic phase is tested in two series:
In the organic phase with 30% (v / v) TBP in n-dodecane in the presence of pentanal oxime, hexanal oxime and for comparison butanal oxime and in the absence of any oxime A first series intended to measure the oxidation kinetics of uranium (IV) after contacting these organic phases with an aqueous phase containing 1.8 mol / L nitric acid and subsequently separating the phases; and Measuring the oxidation kinetics of uranium (IV) in the presence of pentanal oxime and, for comparison, butanal oxime, acetoaldoxime, and hydrazine in an aqueous phase containing -1.3 mol / L nitric acid. The intended second series,
Evaluated.

  In the first series of tests, each organic phase pre-equilibrated with 1.8 M nitric acid and to which oxime was added at a concentration of 0.1 mol / L, if applicable, was added to 6 g / L uranium. The aqueous nitric acid phase containing (IV) was brought into contact with an O / A volume ratio of 2 at room temperature (20-25 ° C.) and under stirring for 10 minutes. 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 measured spectrophotometrically (λ = 653 nm) at time intervals over 200 hours. .

  In the second series of tests, the initial concentrations of uranium (IV) and anti-nitrite (oxime or hydrazine) in the aqueous nitric phase were 66 g / L and 0.2 mol / L, respectively. The time course of uranium (IV) concentration in these aqueous phases was measured spectrophotometrically (λ = 653 nm) at time intervals over 300 days.

  The results of these tests are shown in FIGS. 5 and 6 in the form of curves 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, in connection with 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; Corresponding to the results obtained for naloxime, curve D corresponds to the results obtained in the absence of oxime.

  In FIG. 6, in relation 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; The curve D corresponds to the result obtained for hydrazine, while corresponding to the result obtained for aldoxime.

  As shown in FIG. 5, uranium (IV) is completely stable in the organic phase for at least 15 hours in the presence of oxime, while its oxidation takes less than 8 hours in the absence of any oxime. Complete. Also, in the presence of pentanal oxime and hexanal oxime, less than 10% of uranium (IV) is oxidized in 100 hours, and in the presence of butanal oxime, this is not the case, so pentanal oxime and hexanal oxime are The ability to stabilize uranium (IV) in the organic phase is greater than that of butanal oxime.

  In the aqueous phase, the ability of pentanal oxime to stabilize uranium (IV) is also greater than that of butanal oxime. However, it is smaller than those of acetoaldoxime and hydrazine that are comparable to each other (FIG. 6).

  All these times (days) are still much longer than the length of time the organic and aqueous phases are present during the industrial stripping operation of plutonium.

  These results show that an aqueous nitric acid phase containing a high concentration of uranium (IV) can be converted using pentanal oxime in a single oxime scheme or with acetaldoxime in a two oxime scheme, for example hexanal in the organic phase. It has been shown that either by using an oxime it is possible to stabilize and thereby avoid the use of hydrazine.

Example 3: Anti-nitrite properties of pentanal oxime and hexanal oxime under chemical conditions representative of plutonium reduction stripping operation The anti-nitrite properties of pentanal oxime and hexanal oxime are:
Reduction of plutonium (IV) to plutonium (III) with uranium (IV) and reoxidation of plutonium (III) to plutonium (IV) with nitrous acid;
The destruction of nitrous acid by one of the aforementioned oximes; and the partitioning of the species of interest between the aqueous phase and the organic phase,
In the series of tests shown below as BX1 to BX10, which represent chemical conditions under which plutonium reductive stripping is performed in the PUREX process.

For this purpose, the following was used:
As aqueous phase: containing uranium (VI), uranium (IV) (as a reducing agent for plutonium (IV)), and optionally hydrazine and technetium, in the concentrations shown in Tables 3 and 4 below, 1 mol / L or Solution with 2 mol / L nitric acid; and-as organic phase: 30% of TBP in HTP, containing oxime, uranium (VI), and plutonium (IV) at the concentrations shown in Tables 3 and 4 below (V / v) solution.

  The oxime was added to the organic phase in solid form (the amount of oxime added was adjusted by weighing).

  The organic and aqueous phases are contacted at an O / A volume ratio of 2 at room temperature (20-25 ° C.) and under stirring for 15 minutes (except for test BX3, where the contact time is 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 determined by UV-visible spectroscopy and total plutonium by alpha-spectroscopy. The concentration of uranium (VI) and uranium (IV) in the organic phase was determined by UV-visible spectroscopy and the concentration of total plutonium was determined by alpha-spectroscopy.

From the results of these measurements, U (IV) _cons. / Pu _str. The ratio was measured between the amount of uranium (IV) consumed and the amount of plutonium stripped, as well as the separation factor of plutonium, denoted FD _Pu .

  The results of these tests are shown in Tables 3 and 4 below, which correspond to the results obtained for the tests performed with hexanal oxime (BX1 to BX5, BX8, and BX10). And Table 4 corresponds to the results obtained for the tests (BX6 and BX7) carried out with pentanal oxime.

As shown in these tables:
Consumption for the amount of plutonium stripped for hexanal oxime concentration of 0.1 mol / L in the organic phase and an initial weight ratio (U (IV) / Pu) ranging from 0.8 to 1.5 The amount of uranium (IV) (ratio U (IV) _cons. / Pu _str. ) Is between 0.5 and 0.6; the plutonium reoxidation parasitics are therefore very low and present These results were observed for aqueous phases with nitric acid concentrations of 1 mol / L or 2 mol / L (tests BX1 to BX5);
-Reduction of the hexanal oxime concentration in the organic phase by half (0.05 mol / L vs. 0.1 mol / L), as well as the presence of technetium in the aqueous phase leads to higher consumption of uranium (IV) (ratio U (IV _{..) cons / Pu str =} 1) leads to a, nevertheless it remains moderate (test BX8 and BX10);
-Pentanal oxime can also limit redox phenomena leading to further consumption of uranium (IV), however the ratio U (IV) _cons. Obtained with pentanal oxime _. / Pu _str. Is between 0.6 and 0.8, the performance is slightly lower compared to hexanal oxime (Tests BX8 and BX10).

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

  The results of such monitoring are illustrated in FIGS. 7, 8, and 9, which correspond to organic phases BX5, BX10, and BX6, respectively.

  These figures confirm the ability of pentanal oxime and hexanal oxime to stabilize uranium (IV) in the organic phase. This stabilization is lower in the presence of technetium, but uranium (IV) oxidative kinetics is relatively slow since a half reduction is observed in uranium (IV) concentrations within 50 minutes.

Example 4: Development of a scheme for treating spent nuclear fuel lysate, including a U / Pu distribution step without the use of hydrazine A U / Pu distribution step performed without hydrazine, but in this case An oxime / acetoaldoxime combination is used as an anti-nitrite system, hexanal oxime is used in the organic phase, and acetoaldoxime is used in the aqueous phase to treat spent nuclear fuel solutions. A scheme was developed.

Prior to the development of this scheme, the following were confirmed:
-Firstly, acetoaldoxime can truly replace hydrazine as an anti-nitrite agent in the aqueous phase in the presence of technetium; and-second, hexanal oxime is also intended for the PUREX process and In the organic phase used to carry out the so-called “Np wash” operation, which is the removal of the neptunium stripped during this operation from the aqueous phase obtained from the plutonium stripping operation in the COEX process. (IV) can be stabilized.

4.1-Anti-nitrite properties of acetoaldoxime in the aqueous phase and in the presence of technetium The study examined the anti-nitrite properties of acetoaldoxime in the aqueous phase, the anti-nitrite properties of hydrazine, and technetium Conducted to compare in the presence.

For these studies, the following protocol was applied:
Preparing an aqueous solution containing -9 g / L uranium (IV) and 2 mol / L nitric acid and 0.2 mol / L acetoaldoxime or hydrazine, these solutions being thermostat adjusted to 35 ° C ;
-To these solutions is added an aqueous solution containing 8.88 g / L technetium (VII) (ie 0.09 mol / L) to achieve a final technetium concentration of 100 mg / L or 200 mg / L; and After stirring,
Monitoring the oxidation kinetics of uranium (IV) in the aqueous solution by spectrophotometry (λ = 653 nm) over a period of 100 minutes.

  The results of these tests are shown in FIG. 10, in which the results obtained for acetaldoxime in the presence of 100 mg / L and 200 mg / L Tc correspond to the symbols ■ and X, respectively. On the other hand, the results obtained for hydrazine in the presence of 100 mg / L and 200 mg / L Tc correspond to the symbols ▲ and ●, respectively.

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

  Therefore, it is possible to replace hydrazine as an anti-nitrite agent with acetoaldoxime.

4.2 Stabilization of Uranium (IV) in “Np Wash” Operation Two tests, shown below as BS16 and BS17, were performed using:
As organic phase: 30% (v / v) solution of TBP in HTP with or without 0.1 mol / L hexanal oxime; and as aqueous phase: uranium (VI), acetoaldoxime, plutonium (III), and an aqueous solution using 1.3 mol / L nitric acid, containing technetium in the concentrations shown in Table 5 below; technetium is a 8.88 g / L concentrated Tc (VII) solution. In form, the aqueous phase was added to the aqueous phase just prior to contact with the organic phase.

  The organic and aqueous phases were contacted at volume / volume for 15 minutes at room temperature (20-25 ° C.) and under stirring, after which the phases were separated from each other.

The concentration of uranium (IV) in the aqueous and organic phases was measured and U (IV) _cons. The percentage of uranium (IV) consumed in each test was measured.

  The results are shown in Table 5 below.

  This table shows that the presence of hexanal oxime in the organic phase (Test BS16) allows a 50% reduction in uranium (IV) consumption compared to consumption without this oxime (Test BS17). ing.

4.3 Processing Scheme The developed nuclear fuel solution processing scheme is illustrated in FIG.

In this scheme, two main steps of the first purification cycle of the COEX process are seen: namely:
(1) A process for decontaminating actinides (III) (Americium and Curium) and a number of fission products of uranium and plutonium, and includes:
* Firstly in oxidation state VI, secondly in oxidation state IV and thirdly in oxidation state VI, the organic phase containing 30% (v / v) TBP in HTP allows uranium, plutonium, And the operation called “U / Pu co-extraction” in FIG. 11, intended to extract together neptunium;
* In Fig. 11 "FP" intended to remove fission products, in particular ruthenium and zirconium extracted in "U / Pu co-extraction" from the organic phase obtained from the "U / Pu co-extraction" operation. An operation called "washing";
* An operation called “Tc wash” in FIG. 11 intended to remove technetium by the aqueous phase from the organic phase obtained from “FP wash” extracted in “U / Pu co-extraction”;
* The fraction of neptunium following uranium (IV), plutonium (IV), and technetium in the aqueous phase in “Tc wash” was intended to be recovered in the organic phase in FIG. / Pu co-extraction operation;
And (2) distributing uranium and plutonium in two aqueous streams, one containing uranium and the other containing plutonium and uranium (with a U / Pu weight ratio on the order of 20:80 to 30: 7). And includes the following:
* "Pu / U stripping" in Figure 11 intended to strip plutonium from the organic phase obtained from "Tc wash" and the fraction of uranium contained in this organic phase. This operation is carried out with an aqueous phase comprising uranium (IV) as a reducing agent capable of reducing plutonium to oxidation state III;
* From the aqueous phase obtained from "Pu / U stripping", excess uranium relative to the intended 20:80 to 30:70 U / Pu weight ratio and aqueous in "Pu / U stripping" The fraction of neptunium following plutonium in the phase was intended to be removed, an operation called “Np wash” in FIG. 11; and * from the organic phase obtained from “Pu / U stripping” An operation called “U-stripping” intended to strip uranium and neptunium by the aqueous phase;
It is.

  However, in the scheme illustrated in FIG. 11, the anti-nitrite hydrazine used in the COEX process is replaced by a hexanal oxime / acetoaldoxime combination.

  As can be seen in FIG. 11, hexanal oxime (indicated by HexOx in FIG. 11) takes into account its strong lipophilicity, into the organic phase entering the extractor 5 in which “Np washing” takes place. And just before it enters the extractor 6, it is added to the organic phase obtained from "Tc wash".

  Acetaldoxime (shown in FIG. 11 as AcOx) is added to the circulating aqueous phase in the extractor 6 in view of its hydrophilicity, and this addition is in three different stages of the extractor: stripping. Stage 8 where acetoaldoxime is injected into the aqueous phase used and stage 1 where acetoaldoxime is injected into the aqueous stream used to supply uranium (IV) to this aqueous phase and 4 is implemented.

  Using what was basically obtained for the oximes used in the two phases, the aqueous phase and the organic phase, their partitioning between the aqueous phase and the organic phase used in this process, and The first model was developed that enables simulation of the kinetics of those reactions using nitric acid. These models were implemented in the PAREX code, ie software that allows for the simulation of the distribution of the species of interest in an operation such as, for example, distributing uranium and plutonium into two aqueous streams. It was based on this simulation that the operating parameters were determined to experimentally test the scheme illustrated in FIG.

  FIG. 12 shows uranium in the aqueous phase circulating in the extractors 5 and 6 (firstly for the scheme illustrated in FIG. 11 (curve A) and secondly for a similar scheme using hydrazine (curve B)). Compare the concentration profiles of IV). The ideal profile obtained by neutralizing the reoxidation reaction of plutonium (III) (in the RAREX code) is also illustrated (curve C).

  As shown in this figure, the use of the hexanal oxime / acetoaldoxime combination resulted in a higher uranium (IV) concentration profile than that obtained with hydrazine, thereby in the presence of these oximes. Reduced uranium (IV) consumption is demonstrated.

  The scheme illustrated in FIG. 11 has been successfully implemented in the ATALANT shielded cell process line for an actual solution of spent nuclear fuel. This scheme uses a significant concentration of uranium (IV) (16 g / L) and produces a plutonium stream having a concentration of 10 g / L without any uranium (IV) adjuvant in the “Np wash” operation. While made possible, this adjuvant is necessary in similar schemes using hydrazine. Uranium (IV) consumption is also lower than in the scheme using hydrazine.

  FIG. 13 illustrates the concentration profile of plutonium in the aqueous phase circulating in the extractors 5 and 6, for example experimentally obtained (symbol x) and calculated by the PAREX code (curve-). However, FIG. 14 illustrates concentration profiles of uranium (IV), uranium (VI), and total uranium in the aqueous phase circulating in these same extractors, obtained, for example, experimentally and by computer calculation. In the figure, the symbols x, ◆, and ■ correspond to experimentally obtained uranium (IV), uranium (VI), and total uranium concentration profiles, respectively, while curves A, B, and C are , Corresponding to the concentration profiles of uranium (IV), uranium (VI), and total uranium, respectively obtained by computer calculation.

Table 6 below also shows the uranium concentration ([U (IV)] _{Pu-producing flow} in the aqueous phase obtained from the extractor 5, as obtained experimentally for the scheme illustrated in FIG. ), Plutonium concentration in the aqueous phase obtained from the extractor 5 (indicated by [Pu] _{Pu-producing flow} ), the _flow of uranium (IV) entering the extractor 6 and the flow of Pu entering the same extractor Between uranium (indicated by U (IV) / _Puentering ), the percentage of uranium (IV) consumed (indicated by U (IV) _cons. ), And the plutonium entering the consumed uranium stream (Indicated by U (IV) _cons. / Pu).

  For comparison, this table shows these same concentrations, ratios, and percentages as obtained experimentally for a similar scheme using hydrazine.

Claims (12)

  In the reduction stripping operation of plutonium of at least one aldoxime of the formula R—CH═N—OH, wherein R is a linear or branched hydrocarbon chain having at least 4 carbon atoms. Use as an anti-nitrite agent.   Use according to claim 1, wherein R is a straight or branched hydrocarbon chain having 4 to 12 carbon atoms, and better 4 to 8 carbon atoms.   Use according to claim 2, wherein R is a linear alkyl chain having 4 to 8 carbon atoms.   Use according to claim 3, wherein the aldoxime is pentanal oxime or hexanal oxime. The plutonium reduction stripping operation is:
Contacting the non-water miscible organic phase comprising an extractant and oxidation state IV plutonium in an organic diluent with an aqueous phase comprising nitric acid and a reducing agent capable of reducing plutonium (IV) to plutonium (III). Wherein one of said organic phase and aqueous phase also contains aldoxime; then-separating the so contacted organic phase and aqueous phase;
5. Use according to any one of claims 1 to 4, comprising:   6. Use according to claim 5, wherein the reducing agent is selected from uranium (IV), hydroxylammonium nitrate, alkylated derivatives of hydroxylamine, ferrous sulfamate and sulfamic acid.   Use according to claim 6, wherein the reducing agent is uranium (IV) or hydroxylammonium nitrate.   8. Use according to any one of claims 5 to 7, wherein the extractant is tri-n-alkyl phosphate, preferably tri-n-butyl phosphate.   Use according to any one of claims 1 to 8, wherein the aldoxime is used at a concentration of organic or aqueous phase of 0.01 mol / L to 3 mol / L.   Use according to any one of claims 5 to 9, wherein the aqueous phase further comprises an oxime that is non-extractable by the organic phase.   Use according to claim 10, wherein the oxime that is non-extractable by the organic phase is acetoaldoxime.   12. Use according to any one of the preceding claims, wherein the plutonium reduction stripping operation is one of a PUREX or COEX plutonium stripping operation.

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