PROCESS FOR TREATING A USE NUCLEAR FUEL COMPRISING A DECONTAMINATION STEP OF URANIUM (VI) IN AT LEAS

专利摘要:
The invention relates to a method for treating a spent nuclear fuel which comprises a step of decontaminating uranium (VI) in one or more actinides (IV) and, more particularly in neptunium and / or plutonium, by complexation of this (these) actinide (s) (IV). This method comprises a step of decontaminating uranium (VI) in at least one actinide (IV), which decontamination step comprises at least one actinide (IV) de-extraction operation of an organic phase which is immiscible with water and in which the uranium (VI) and the actinide (IV) are present, by contacting the organic phase with an aqueous phase comprising nitric acid and at least one complexing agent which complex more strongly actinides (IV) than uranium (VI), then separation of the organic phase from the aqueous nitric phase, and is characterized in that said at least one complexing agent is a diglycolamide. Applications: treatment of spent nuclear fuels.
公开号:FR3015760A1
申请号:FR1363251
申请日:2013-12-20
公开日:2015-06-26
发明作者:Gilles Bernier；Christian Sorel；Manuel Miguirditchian；Coralie Balaguer；Estelle Ameil
申请人:Areva NC SA；Commissariat a lEnergie Atomique CEA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
IPC主号:

专利说明:

[0001] PROCESS FOR PROCESSING USED NUCLEAR FUEL COMPRISING A DECONTAMINATION STAGE OF URANIUM (VI) IN AT LEAST ONE ACTINIDE (IV) BY COMPLEXATION OF THIS ACTINIDE (IV) DESCRIPTION TECHNICAL FIELD The present invention relates to the field of the treatment of spent nuclear fuel. More specifically, it relates to a process for treating a spent nuclear fuel which comprises a step of decontaminating uranium (VI) in one or more actinides (IV) and, more particularly in neptunium and / or plutonium, by complexation of this (these) actinide (s) (IV). STATE OF THE PRIOR ART Used nuclear fuel treatment plants currently use the PUREX process (for Plutonium Uranium Refining by Extraction) to recover the uranium and plutonium present in these fuels. This is achieved by carrying out several purification cycles by liquid-liquid extraction. The extractant used is tri-n-butyl phosphate, which has a particular affinity for uranium and plutonium. The PUREX process, as it is used in the factories (UP2-800, UP3) at La Hague in France, comprises schematically three purification cycles, namely: a first cycle, which aims to decontaminate the uranium and plutonium vis-à-vis americium, curium and fission products, and to partition uranium and plutonium into two aqueous streams; and two complementary cycles, called "second cycle uranium" and "second cycle plutonium" respectively, which aim to purify uranium and plutonium separately after partitioning.
[0002] As shown in Figure 1 which shows a simplified diagram of the first cycle of the PUREX process, this cycle begins with an operation, called "U / Pu coextraction" in this figure, which consists of jointly extracting uranium and plutonium, the first in the oxidation state VI, the second in the oxidation state IV, of an aqueous phase in which they are located. This aqueous phase is obtained by dissolving spent fuel in nitric acid and clarifying the mixture thus obtained. It is commonly called dissolution liquor. It typically contains from 200 to 250 g / L of uranium for 2 to 3 g / L of plutonium. It also contains neptunium, americium, curium and fission products. The co-extraction of uranium and plutonium is carried out by means of a water-immiscible organic phase, which comprises an extractant having a high affinity for uranium (VI) and plutonium (IV), in the species tributyl phosphate (or TBP) that is used in solution at 30% (v / v) in an organic diluent, in this case a dodecane (hydrogenated tetrapropylene or TPH). Uranium and plutonium thus pass into the organic phase while americium, curium and most of the fission products remain in the aqueous phase. This co-extraction is followed by two washing operations of the organic phase, called "PF wash" and "Tc wash", which are carried out by means of aqueous nitric phases of different acidities in order to remove the organic phase fraction. fission products and, especially technetium, having been extracted together with uranium and plutonium. The "Tc wash" is coupled to a complementary operation of co-extraction of uranium and plutonium, denoted "complementary coextraction U / Pu", which is carried out using an organic phase, of the same composition as that used for the "U / Pu co-extraction", in order to recover the fraction of uranium and plutonium that may have followed the technetium in the aqueous phase during the "Tc wash". The aqueous phase or phases resulting from these co-extraction and washing operations, which are given the name of raffinates and which are loaded with americium, curium and fission products, are removed from the cycle, whereas the organic phase, which is it, loaded with uranium (VI) and plutonium (IV), is directed towards an area at which the partition of these two elements is carried out. This partition includes: - an operation, called "Pu extraction", which aims to extract the plutonium from the organic phase resulting from the coextraction and washing operations by means of a nitric aqueous phase of low acidity, including uranous nitrate; to reduce the plutonium (IV), which is very extractable by TBP, plutonium (III) which, it is only very little and without reducing the uranium, and hydrazinium nitrate, denoted NH in Figure 1, which acts as an anti-nitrous agent; - An operation, called "dam Pu", which aims to complete the extraction of plutonium from the organic phase by means of a nitric aqueous phase, also low acidity and comprising uranous nitrate and hydrazine; and an operation, called "U-stripping", which aims to extract the uranium (VI) from said organic phase by means of a very dilute aqueous nitric phase. The plutonium de-extraction of the organic phase accompanied by a partial desextraction of uranium, the partition includes, in addition, an operation, called "wash U", which aims to remove the uranium thus desextract from the aqueous phase nitric acid resulting from the "Pu desextraction" by means of an organic phase, of the same composition as those used for the "U / Pu coextraction" and the "U / Pu complementary coextraction". This gives at the end of the first cycle: * a first aqueous stream which comprises more than 99.9% of the plutonium initially present in the dissolution liquor and which no longer comprises uranium; and a second aqueous stream which comprises more than 99.9% of the uranium initially present in the dissolution liquor and no longer comprises plutonium. The first aqueous stream from the first cycle is then subjected to the "second plutonium cycle" whose purpose is to complete the decontamination of plutonium vis-à-vis the fission products that may still be present in the trace state in this case. flux. Thereafter, this stream, which includes plutonium, is directed to an area where the plutonium is converted to oxide (PuO2) and stored in this form for later use in the manufacture of MOX nuclear fuel pellets.
[0003] At the same time, the second aqueous stream from the first cycle is subjected to the "second uranium cycle", whose main objective is to separate uranium from neptunium. Indeed, in the first purification cycle, most of the neptunium present in the dissolution liquor is extracted, mainly in the form of neptunium (VI), along with uranium and plutonium. During the reductive de-extraction of the plutonium, the neptunium (VI) is reduced by the uranous nitrate in neptunium (IV), state in which it is extractable by the TBP. Neptunium thus closely follows uranium in all the operations of the first purification cycle, hence the need to subject the second aqueous stream, loaded with uranium, which is derived from the partition, to a complementary purification cycle. , allowing to decontaminate this uranium, mainly in neptunium, before it is converted into uranium oxide. Recently, a major development of the PUREX process, called the COEXTM process (for COEXtraction), has been proposed in the PCT international application published under number WO 2007/135178 (hereinafter reference [1]). Indeed, while ensuring a recovery and purification of uranium and plutonium comparable to those obtained in the PUREX process, this development can significantly reduce the risk of diversion of plutonium for military purposes. It also makes it possible to produce an aqueous stream that comprises a purified mixture of plutonium, uranium and, optionally, neptunium, that is to say totally decontaminated into fission products, and to use this stream to feed a workshop. said "co-conversion" whose function is to prepare a mixed oxide (U, Pu) 02 or (U, Pu, Np) 02 directly usable for the manufacture of nuclear fuel type MOX (for Mixed OXide Fuel).
[0004] To do this, the COEXTM process provides, after coextraction operations of uranium and plutonium and washing the organic phase resulting from this co-extraction, that is carried out in a manner similar to those used in the first purification cycle of the PUREX process, to partition the uranium and plutonium so as to obtain a first aqueous stream comprising plutonium, uranium and, optionally, neptunium, and a second aqueous stream comprising uranium and, possibly, neptunium but not including plutonium. It also plans to maintain, in all operations downstream of this partition, plutonium in the presence of uranium and, optionally, neptunium, until the mixed (U, Pu) O 2 or (U) oxide is obtained. Pu, Np) 02. In the COEXTM process versions in which the management of neptunium is designed so that all or part of this element follows the uranium in the second aqueous stream from the partition - and which are those illustrated in Figures 1, 2 and 4 of the reference [1] -, one finds the same necessity as in the PUREX process, namely that of subjecting this second aqueous flow to a "second uranium cycle" to rid the uranium of neptunium before its conversion into oxide of uranium. In view of the realization of new spent nuclear fuel treatment plants, it would be desirable to simplify the PUREX and COEXTM processes (for the latter, in its versions requiring a "second uranium cycle") so as to optimize both the costs of investment, operation and maintenance of such plants, without, however, affecting the performance of these processes in terms of efficiency and quality of treatment of spent nuclear fuels. Indeed, the economy of even a single purification cycle as the "second cycle uranium" would reduce not only the number of equipment and equipment necessary for the implementation of the treatment process, but also the volume of reagents consumed, the volume of effluents to be treated, the duration of the process and, consequently, to reduce the size of the plants, their construction costs and their operating costs.
[0005] A method for suppressing the "second uranium cycle" of the PUREX process has already been proposed in the PCT International Application published under the number WO 2005/052950 (hereinafter reference [2]). This process is based on the introduction in the first purification cycle of an operation to decontaminate uranium into neptunium. This operation consists of putting the organic phase which comes from either the "Pu extraction" operation or the "Pu dam" operation in contact with a nitric aqueous phase comprising a lacunary heteropolyanion which more strongly complexes the actinides (IV) and in particular, neptunium (IV) in acidic aqueous phase that it does not complex uranium (VI). Thus, neptunium (IV) tends to pass into the aqueous phase while uranium (VI) remains in the organic phase. The lacunar heteropolyanion is typically a heterotungstate such as arsenotungstate, silicotungstate or germa no-tungstate. However, this method has the major disadvantage of using actinide (IV) complexing agents which, in addition to being in the form of salts, contain tungsten atoms and a metalloid (arsenic, silicon or germanium) which, on an industrial scale, significantly complicates the management of effluents generated by the decontamination of uranium into neptunium. The inventors therefore set themselves the goal of providing a method which, while allowing the "second uranium cycle" of the PUREX and COEXTM processes to be eliminated, is free from the drawback of the method described in reference [2], so as not to add to the constraints inherent in the PUREX and COEXTM processes additional constraints, particularly in terms of management of effluents produced. However, as part of their work, the inventors have found that the use of diglycolamides as actinide (IV) complexing agents makes it possible to very advantageously replace the use of lacunar heteropolyanions as proposed in reference [2], no only because diglycolamides represent a family of non-saline compounds, which respond to the CHON principle (i.e. they consist only of carbon, hydrogen, oxygen and nitrogen atoms ) and which generate gaseous products after degradation, but also because they lead to neptunium decontamination factors which are, for contact times organic phase / aqueous phase comparable, very significantly higher than those obtained with gap heteropolyanions. In particular, the inventors have found that it is possible to obtain, for contact times organic phase / aqueous phase of a few minutes in mixer-settlers, decontamination factors of uranium in neptunium that meet the specification. more stringent has been defined to date by the UNIREP (for UNIted REProcessors) standards for the decontamination of uranium in neptunium and that which is the one concerning the UOX3 fuels (fuels initially enriched to 4.7% in 235U and subjected to a burn rate of 60 GWjt-1). And it is on these findings that the present invention is based. DISCLOSURE OF THE INVENTION The invention proposes a process for treating a spent nuclear fuel, which comprises decontamination of uranium (VI) in one or more actinides (IV), which decontamination comprises a process for the removal of the actinide (IV) or actinides (IV) of an organic phase, immiscible with water and in which uranium (VI) and actinide (IV) or actinides (IV) are present, by setting contacting the organic phase with an aqueous phase comprising nitric acid and at least one complexing agent which more strongly complexes the actinides (IV) than the uranium (VI), then separating the organic phase from the aqueous phase, and which is characterized in that said at least one complexing agent is a diglycolamide. Thus, the method of the invention uses the ability of diglycolamides to complex in the aqueous phase much more strongly actinides (IV) than actinides (VI) and to allow, when actinides (IV) are present in a phase organic, together with uranium (VI), and that this organic phase is brought into contact with an aqueous phase in which is a diglycolamide, the selective transfer of actinides (IV) from the organic phase to the aqueous phase.
[0006] It should be noted that the ability of diglycolamides to complex actinides (IV) preferentially to actinides (VI) is known per se (Sasaki et al., Analytical Sciences 2007, 23 (6), 727, hereinafter referred to [3]). What is completely new is that this ability is used to decontaminate uranium (VI) with actinides (IV) as part of a process for the treatment of spent nuclear fuel and, in particular, as part of the first purification cycle of the PUREX and COEXTM processes and, what is totally unexpected, is the fact that it leads to decontamination levels of uranium in actinides (IV) such that it is possible to suppress the second uranium purification cycle included in these processes, provided that the decontamination of uranium with respect to the fission products (mainly ruthenium and technetium) is, moreover, sufficient. It is recalled that the diglycolamides are compounds of formula (I) or of formula (II) below: ## STR2 ## R1 (R2) NC (O) -CH2-O-CH2-COOH (II) wherein R1, R2, R3 and R4 are typically alkyl groups.
[0007] According to the invention, the diglycolamide is preferably chosen from diglycolamides of formula (I) in which the total number of carbon atoms that RI-, R2, R3 and R4 together have is at most equal to 12 and diglycolamides of formula (II) in which the number of carbon atoms that R 1 and R 2 together are at most equal to 12, so as to have sufficient hydrophilicity to be used in the aqueous phase. Such diglycolamides are in particular N, N, N ', N'-tetramethyldiglycolamide (or TMDGA, which corresponds to formula (I) in which R 1 = R 2 = R 3 = R 4 = CH 3), N, N, N' , N'-tetraethyldiglycolamide (or TEDGA, which corresponds to the formula (I) in which R1- = R2 = R3 = R4 = C2H5), N, N, N ', N'-tetrapropyldiglycolamide (or TPDGA, which corresponds to the formula (I) in which R1- = R2 = R3 = R4 = C3H7) and N, N-dipropyldiglycolamic acid (or DPDGAc, which corresponds to formula (II) in which R1 = R2 = C3H7). Among these diglycolamides, TEDGA and TPDGA were found to have a higher complexing activity of actinides (IV) than that of TMDGA and DPDGAc. Also, preference is given to TEDGA and TPDGA, TEDGA being particularly preferred because, of these two diglycolamides, it is the one that is the most soluble in water and the least extractable by the most conventionally used extractant in the treatment of spent nuclear fuels, namely TBP. Be that as it may, diglycolamide is advantageously present in the aqueous phase at a concentration ranging from 0.01 to 0.1 mol / l and, more preferably, from 0.02 to 0.05 mol / l. As for nitric acid, it is preferably present in this aqueous phase at a level of 0.2 to 3 mol / l and, more preferably, from 0.5 to 1.5 mol / l. According to a preferred arrangement of the process of the invention, the decontamination of uranium (VI) into actinide (IV) or actinides (IV) further comprises a washing operation of the aqueous phase resulting from the desextraction of the actinide (IV) or actinides (IV), by bringing this aqueous phase into contact with an organic phase comprising an extractant of uranium (VI), and then separating the organic phase from the aqueous phase.
[0008] This washing operation, which is intended to remove from the aqueous phase resulting from the extraction of actinide (IV) or actinides (IV), the fraction of uranium (VI) which may have been de-extracted in conjunction with this actinide ( IV) or these actinides (IV), is preferably carried out using an organic phase comprising TBP as extractant, in which case the latter is typically used in solution in an organic diluent of the dodecane type, in an equal or substantially volume ratio. equal to 30/70. The assembly formed by the de-extraction operations of actinide (IV) or actinides (IV) and washing the aqueous phase resulting from this extraction will be referred to hereinafter as "a-complexing barrier".
[0009] In accordance with the invention, actinide (IV) or actinides (IV) are preferably selected from neptunium (IV), plutonium (IV) and thorium (IV) and, more particularly, from neptunium (IV ) and plutonium (IV). According to a first preferred embodiment of the process of the invention, the decontamination of uranium (VI) into one or more actinides (IV) is a decontamination of uranium (VI) into neptunium (IV). According to a first provision of this first preferred embodiment, the process of the invention results from the introduction of an "alpha-complexing barrier" in the first purification cycle of a PUREX process in order to decontaminate the uranium (VI) into neptunium (IV) during the partitioning step of uranium and plutonium, in which case the process of the invention preferably comprises: a) a step of decontaminating uranium and plutonium present in an aqueous phase resulting from the dissolution of a spent nuclear fuel in nitric acid, with respect to actinides (III) and fission products also present in this phase, which step comprises: a) at minus a co-extraction operation of the uranium, in the oxidation state VI, and plutonium, in the IV oxidation state, of the aqueous phase, by contacting this aqueous phase with a phase organic compound comprising TBP in an organic diluent, then separatio n of the organic phase of the aqueous phase; and a2) at least one washing operation of the organic phase derived from ai) to remove from this aqueous phase the fraction of fission products that have been extracted during ai), by contacting said organic phase with an aqueous phase comprising nitric acid, and then separating the organic phase from the aqueous phase; whereby an organic phase is obtained which comprises uranium (VI), plutonium (IV) and neptunium (VI); b) a step of partitioning the uranium and plutonium present in the organic phase resulting from step a) into two aqueous phases, a first aqueous phase comprising decontaminated uranium and neptunium plutonium and a second aqueous phase comprising decontaminated uranium to plutonium and neptunium, which step comprises: b1) a plutonium extraction operation in the organic phase resulting from step a), the plutonium being extracted in the oxidation state III by means of contacting the organic phase resulting from step a) with an aqueous phase comprising nitric acid, a reducing agent, for example uranyl nitrate, which reduces the plutonium (IV) to plutonium (III) and neptunium (VI) to neptunium (IV) without reducing the uranium (VI), and an anti-nitrous agent, for example hydrazinium nitrate, and then separating the organic phase from the aqueous phase; b2) a washing operation of the organic phase resulting from b1) to remove from this organic phase the plutonium fraction that has not been de-extracted during b1), by bringing said organic phase into contact with an aqueous phase comprising nitric acid, the same reducing agent and the same anti-nitrous agent as those used for the removal of plutonium, and then separating the organic phase from the aqueous phase; b3) a washing operation of the aqueous phase resulting from b1) to remove from this aqueous phase the fraction of uranium (VI) and neptunium (IV) which has been de-extracted during b1), by contacting said phase aqueous solution with an organic phase comprising TBP in an organic diluent, and then separating the organic phase from the aqueous phase; b4) the decontamination of uranium (VI) into neptunium (IV), this decontamination comprising a neptunium (IV) desextraction operation present in the organic phase resulting from b2), by bringing this organic phase into contact with a phase aqueous solution comprising nitric acid and diglycolamide, and then separating the organic phase from the aqueous phase, and a washing operation of the aqueous phase resulting from the neptunium (IV) de-extraction operation, by bringing this aqueous phase with an organic phase comprising TBP in an organic diluent, and then separating the organic phase from the aqueous phase; and b5) a uranium (VI) de-extraction operation present in the organic phase resulting from the neptunium (IV) dextraction operation of b4), by bringing this organic phase into contact with an aqueous phase comprising nitric acid, and then separating the organic phase from the aqueous phase. A first aqueous phase is thus obtained which comprises plutonium (III) decontaminated with uranium and neptunium and which is that resulting from b3), a second aqueous phase which comprises uranium (VI) decontaminated with plutonium and with neptunium and which is that resulting from b5), and a third aqueous phase which comprises neptunium (IV) and which is that resulting from b4). According to another provision of this first preferred embodiment, the process of the invention results from the introduction of an "alpha-complexing barrier" in the first purification cycle of a COEXTM process in order to decontaminate the uranium (VI) to neptunium (IV) during the partitioning of uranium and plutonium, in which case the process of the invention preferably comprises: a) a step of decontaminating uranium and plutonium present in a aqueous phase resulting from the dissolution of a spent nuclear fuel in nitric acid, with respect to actinides (III) and fission products also present in this phase, which step is identical to step a) previously described and leads, like it, to an organic phase which comprises uranium (VI), plutonium (IV) and neptunium (VI); b) a step of partitioning the uranium and plutonium present in the organic phase resulting from step a) into two aqueous phases, a first aqueous phase comprising plutonium and uranium decontaminated in neptunium and a second aqueous phase; comprising decontaminated uranium with plutonium and neptunium, which step comprises: b1) a process for the extraction of plutonium and a fraction of the uranium present in the organic phase resulting from step a), the plutonium being extracted in the oxidation state III by contacting the organic phase resulting from step a) with an aqueous phase comprising nitric acid, a reducing agent, for example uranyl nitrate, which reduces the plutonium (IV) into plutonium (III) and neptunium (VI) into neptunium (IV) without reducing uranium (VI), and an anti-nitrous agent, for example hydrazinium nitrate, and then separating the organic phase from the aqueous phase; b2) a washing operation of the organic phase resulting from b1) to remove from this organic phase the plutonium fraction that has not been de-extracted during b1), by bringing said organic phase into contact with an aqueous phase comprising nitric acid, the same reducing agent and the same anti-nitrous agent as those used for the plutonium desextraction operation, and then separating the organic phase from the aqueous phase; b3) a washing operation of the aqueous phase from b1) to remove from this aqueous phase the fraction of neptunium (IV) having been deextracted during b1), by contacting this aqueous phase with an organic phase comprising TBP in an organic diluent, then separation of the organic phase from the aqueous phase; b4) the decontamination of uranium (VI) into neptunium (IV), this decontamination comprising a neptunium (IV) desextraction operation present in the organic phase resulting from b2), by bringing this organic phase into contact with a phase aqueous composition comprising nitric acid and diglycolamide, and then separation of the organic phase from the aqueous phase, and a washing operation of the aqueous phase resulting from the neptunium (IV) desextraction operation by contacting this phase aqueous solution with an organic phase comprising TBP in an organic diluent, and then separating the organic phase from the aqueous phase; and b5) a uranium extraction operation present in the organic phase resulting from the neptunium (IV) dextraction operation of b4), by bringing this organic phase into contact with an aqueous phase comprising nitric acid; and then separating the organic phase from the aqueous phase. A first aqueous phase is thus obtained which comprises plutonium (III) and uranium (VI) decontaminated in neptunium and which is that resulting from b3), a second aqueous phase which comprises uranium (VI) decontaminated in neptunium. and plutonium, which is that from b5), and a third aqueous phase which comprises neptunium (IV) and which is that from b4).
[0010] According to a second preferred embodiment of the process of the invention, the decontamination of uranium (VI) into one or more actinides (IV) is a decontamination of uranium (VI) into neptunium (IV) and into plutonium (IV). According to a first disposition of this second preferred embodiment, the process of the invention results from the introduction of an "alpha-complexing barrier" in the first purification cycle of a PUREX process in order to decontaminate the uranium (VI) into neptunium (IV) and plutonium (IV) during the partitioning of uranium and plutonium, in which case the process of the invention preferably comprises: a) a step of decontaminating uranium and plutonium present in an aqueous phase resulting from the dissolution of a spent nuclear fuel in nitric acid, vis-à-vis the actinides (III) and fission products also present in this phase, which step is identical in step a) previously described and leads, like it, to an organic phase which comprises uranium (VI), plutonium (IV) and neptunium (VI); b) a step of partitioning the uranium and plutonium present in the organic phase resulting from step a) into two aqueous phases, a first aqueous phase comprising decontaminated uranium and neptunium plutonium and a second aqueous phase comprising decontaminated uranium to plutonium and neptunium, which step comprises: b1) a plutonium extraction operation in the organic phase resulting from step a), the plutonium being extracted in the oxidation state III by means of contacting the organic phase resulting from step a) with an aqueous phase comprising nitric acid, a reducing agent, for example uranyl nitrate, which reduces the plutonium (IV) to plutonium (III) and neptunium (VI) to neptunium (IV) without reducing the uranium (VI), and an anti-nitrous agent, for example hydrazinium nitrate, and then separating the organic phase from the aqueous phase; b2) a washing operation of the aqueous phase from b1) to remove from this phase the fraction of uranium (VI) and neptunium (IV) having been de-extracted during b1), by contacting this aqueous phase with an organic phase comprising TBP in an organic diluent, and then separating the organic phase from the aqueous phase; b3) the decontamination of the uranium (VI) in neptunium (IV) and in plutonium (IV), this decontamination comprising a process for the extraction of neptunium (IV) and plutonium (IV) present in the organic phase resulting from b1) by bringing this organic phase into contact with an aqueous phase comprising nitric acid and diglycolamide, and then separating the organic phase from the aqueous phase, and washing the aqueous phase resulting from the de-extraction operation. neptunium (IV) by contacting this aqueous phase with an organic phase comprising TBP in an organic diluent, and then separating the organic phase from the aqueous phase; and b4) a uranium extraction operation present in the organic phase resulting from the operation of the extraction of neptunium (IV) and plutonium (IV) from b3), by contacting this organic phase with an aqueous phase comprising nitric acid, and then separating the organic phase from the aqueous phase. A first aqueous phase is thus obtained which comprises plutonium (III) decontaminated with uranium and neptunium and which is that resulting from b2), a second aqueous phase which comprises uranium (VI) decontaminated with neptunium and plutonium and which is that resulting from b4), and a third aqueous phase which comprises neptunium (IV) and plutonium (IV) decontaminated in uranium (VI) and which is that resulting from b3). According to another provision of this second preferred embodiment, the method of the invention results from the introduction of an "alpha-complexing barrier" in the first purification cycle of a COEXTM process in order to decontaminate the uranium (VI) into neptunium (IV) and plutonium (IV) during the partitioning of uranium and plutonium, in which case the process of the invention preferably comprises: a) a step of decontaminating uranium and plutonium present in an aqueous phase resulting from the dissolution of a spent nuclear fuel in nitric acid, vis-à-vis the actinides (III) and fission products also present in this phase, which step is identical in step a) previously described and leads, like it, to an organic phase which comprises uranium (VI), plutonium (IV) and neptunium (VI); b) a step of partitioning the uranium and plutonium present in the organic phase resulting from step a) into two aqueous phases, a first aqueous phase comprising plutonium and uranium decontaminated in neptunium and a second aqueous phase; comprising decontaminated uranium in neptunium and plutonium, which step comprises: b1) an operation for the desextraction of the plutonium and a fraction of the uranium present in the organic phase resulting from step a), the plutonium being de-extracted in the oxidation state III by contacting the organic phase resulting from step a) with an aqueous phase comprising nitric acid, a reducing agent, for example uranyl nitrate, which reduces the plutonium (VI) into plutonium (III) and neptunium (VI) into neptunium (IV) without reducing uranium (VI), and an anti-nitrous agent, for example hydrazinium nitrate, and then separating the organic phase from the aqueous phase; b2) a washing operation of the aqueous phase from b1) to remove from this aqueous phase the fraction of neptunium (IV) having been deextracted during b1), by contacting said aqueous phase with an organic phase comprising TBP in an organic diluent, then separation of the organic phase from the aqueous phase; b3) the decontamination of the uranium (VI) in neptunium (IV) and in plutonium (IV), this decontamination comprising a process for the extraction of neptunium (IV) and plutonium (IV) present in the organic phase resulting from b1) by bringing this organic phase into contact with an aqueous phase comprising nitric acid and diglycolamide, and then separating the organic phase from the aqueous phase, and washing the aqueous phase resulting from the de-extraction operation. neptunium (IV) by contacting this aqueous phase with an organic phase comprising TBP in an organic diluent, and then separating the organic phase from the aqueous phase; and b4) a uranium extraction operation present in the organic phase resulting from the neptunium (IV) de-extraction operation of b3), by bringing this organic phase into contact with an aqueous phase comprising nitric acid and then separating the organic phase from the aqueous phase. A first aqueous phase is thus obtained which comprises plutonium (III) and uranium (VI) decontaminated in neptunium and which is that resulting from b2), a second aqueous phase which comprises uranium (VI) decontaminated with neptunium. and plutonium, which is that from b4), and a third aqueous phase which comprises neptunium (IV) and plutonium (IV) decontaminated in uranium (VI) and which is that resulting from b3). In all cases, the operation of de-extraction of neptunium (IV) or of desextraction of neptunium (IV) and plutonium (IV) is preferably carried out with an aqueous solution comprising from 0.2 to 3 mol / L of nitric acid and from 0.01 to 0.1 mol / L of TEDGA. Furthermore, the uranium desextraction operation (that is to say the operation corresponding to b5) in the first preferred embodiment of the invention and b4) in the second embodiment of the invention. preferred embodiment of the invention) is preferably carried out with an aqueous solution comprising from 0.005 to 0.05 mol / L of nitric acid and at a temperature of 45 to 55 ° C. Other features and advantages of the invention will emerge from the additional description which follows and which relates to examples of implementation of the method of the invention as well as experimental tests to validate this process. It goes without saying that these examples are given only as illustrations of the subject of the invention and should in no way be interpreted as a limitation of this object.
[0011] BRIEF DESCRIPTION OF THE FIGURES FIG. 1, already commented on, represents a simplified diagram of the first purification cycle of the PUREX process as it is implemented in the La Hague factories in France.
[0012] FIG. 2 represents a simplified diagram of a first example of implementation of the process of the invention, in which the latter results from the introduction of an "a-complexing barrier" in the first purification cycle of the PUREX process. illustrated in Figure 1 to decontaminate uranium (VI) neptunium (IV) during the partition of uranium and plutonium.
[0013] FIG. 3 represents a simplified diagram of a second example of implementation of the method of the invention, in which the latter results from the substitution of the "Pu dam" by an "a-complexing barrier" in the first purification cycle. the PUREX process illustrated in Figure 1 to decontaminate uranium (VI) neptunium (IV) and plutonium (IV) during the partition of uranium and plutonium.
[0014] FIG. 4 represents a simplified diagram of a third example of implementation of the method of the invention, in which the latter results from the introduction of an "a-complexing barrier" in the first purification cycle of the COEXTM process. as illustrated in Figure 1 of reference [1] to decontaminate uranium (VI) to neptunium (IV) during the partition of uranium and plutonium.
[0015] FIG. 5 represents a simplified diagram of a fourth example of implementation of the process of the invention, in which the latter results from the substitution of the "Pu dam" by an "a-complexing barrier" in the first purification cycle. of the COEXTM process as illustrated in Figures 1 and 4 of reference [1] to decontaminate uranium (VI) into neptunium (IV) and plutonium (IV) during the partition of uranium and plutonium . FIG. 6 represents the scheme used for experimental tests for the implementation of an "a-complexing barrier" in mixer-decanter batteries. In FIGS. 1 to 5, the rectangles represent multi-stage extractors such as those conventionally used in the treatment of spent nuclear fuels (mixer-settlers, pulsed columns, centrifugal extractors); the organic phases entering or leaving these extractors are symbolized by solid lines while the aqueous phases entering or leaving these extractors are symbolized by dashed lines.
[0016] Moreover, in FIGS. 2 to 5, the "a-complexing barrier" that comprises the exemplary embodiments of the method of the invention illustrated in these figures is written in a dotted box so as to make it more visible. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS Referring firstly to FIG. 2 which represents a first example of implementation of the method of the invention. In this example, the process of the invention results from the introduction of an "a-complexing barrier" in the first purification cycle of the PUREX process illustrated in FIG. 1 in order to decontaminate uranium (VI) into neptunium. (IV) during the partition of uranium and plutonium.
[0017] The "a-complexing dam" is therefore used in addition to the "Pu dam". The method of the invention comprises, firstly, a step of decontaminating uranium and plutonium in americium, curium and fission products, similar to that which exists in the first purification cycle of the PUREX process. This first step includes: an operation, called "U / Pu co-extraction", which aims at jointly extracting uranium and plutonium, the first in the state of oxidation (VI), the second in the state of oxidation (IV) of a dissolution liquor by bringing this liquor into contact with an organic phase comprising TBP in solution at approximately 30% (v / v) in an organic diluent, for example a dodecane such as TPH , then separation of the two phases; an operation, called "washing PF", which aims at removing from the organic phase resulting from the "U / Pu co-extraction" the fraction of the fission products, in particular ruthenium and zirconium, having been extracted during this process. coextraction, by contacting this organic phase with a nitric aqueous phase of moderate acidity, for example an aqueous solution of nitric acid 1 to 3 M, and then separation of the two phases; an operation, called "washing Tc", which aims to remove the organic phase from the "PF wash" fraction of technetium that was extracted during the "co-extraction U / Pu", by contacting this phase organic with a nitric aqueous phase of moderate acidity but higher than that of the nitric aqueous phase used for "washing PF", for example an aqueous solution of nitric acid 3 to 5 M, and then separation of the two phases; and an operation, called "complementary co-extraction U / Pu", which aims to recover in the organic phase the uranium and plutonium fractions having followed the technetium in the aqueous phase during the "Tc wash", by contacting the the aqueous phase resulting from this washing with an organic phase also comprising TBP in solution at approximately 30% (v / v) in an organic diluent, then separation of the two phases. Four phases are thus obtained: - the two aqueous phases (or raffinates) resulting from the "co-extraction U / Pu" and "complementary co-extraction U / Pu", which are loaded with fission products and for the first of they, in americium and curium, and which are eliminated from the cycle; the organic phase resulting from the "complementary co-extraction U / Pu", which is sent to the extractor where the "U / Pu co-extraction" takes place to be added to the organic phase circulating in this extractor; and the organic phase resulting from the "Tc wash", which is charged with uranium (VI), with plutonium (IV) but also with neptunium (VI) since the major part of the neptunium present in the dissolution liquor is extracted by the TBP . As in the first purification cycle of the PUREX process, this organic phase is directed to an area at which a step of partitioning uranium and plutonium into two aqueous phases is carried out. On the other hand, this partitioning step is carried out differently from that of the first purification cycle of the PUREX process since it comprises an "a-complexing barrier" between the "Pu dam" and the "U-stripping". Also, as can be seen in FIG. 2, the partitioning step comprises: an operation, called "Pu extraction", which aims to extract the plutonium from the organic phase resulting from the "Tc wash", by bringing this organic phase with a nitric aqueous phase of low acidity, for example an aqueous solution of nitric acid 0.05 to 2 M, comprising, on the one hand, a reducing agent, for example uranous nitrate (or U (IV)) and, on the other hand, an anti-nitrous agent, for example hydrazinium nitrate, and then separation of the two phases; the reducing agent serves to reduce plutonium (IV) to plutonium (III) and neptunium (VI) to neptunium (IV) without reducing uranium (VI), while the anti-nitrous agent is used to stabilize both the reducing agent and the plutonium (III) by destroying the nitrous acid which tends to form in the aqueous phase; an operation, referred to as the "Pu dam", which aims to perfect the plutonium's desextraction by contacting the organic phase resulting from the "Pu Desextraction" with a nitric aqueous phase of low acidity, for example an aqueous solution of 0.05 to 2 M nitric acid, comprising the same reducing agent and the same anti-nitrous agent as those used for the "Pu desextraction", then separation of the two phases; an operation, referred to as "first wash U", which aims to remove from the aqueous phase resulting from the "Pu desextraction" the fraction of uranium that has been de-extracted in conjunction with the plutonium, by contacting this aqueous phase with a phase organic composition also comprising TBP in solution at approximately 30% (v / v) in an organic diluent, followed by separation of the two phases; an operation, called "Np desextraction", which aims to extract the neptunium (IV) present in the organic phase resulting from the "Pu dam", by contacting this organic phase with a nitric aqueous phase, for example an aqueous solution of 0.2 to 3 M nitric acid, which comprises a diglycolamide, for example TEDGA at a concentration of 0.01 to 0.1 mol / L, then separation of the two phases; an operation, called "second wash U", which aims to remove from the aqueous phase resulting from the "Np desextraction" the uranium fraction having been desextracted together with neptunium, by contacting this aqueous phase with an organic phase also comprising TBP in solution at approximately 30% (v / v) in an organic diluent, followed by separation of the two phases; and an operation, called "U-stripping", which aims to extract the uranium from the organic phase resulting from the "Np-stripping", by contacting this organic phase with a very dilute aqueous nitric phase, for example a solution aqueous nitric acid 0.005 to 0.05 M, then separation of the two phases. Four phases are thus obtained, namely: the aqueous phase resulting from the "first washing U", which comprises plutonium (III) decontaminated with uranium and with neptunium and which can be directed, after an oxidation operation (not shown on Figure 2) to bring the plutonium back to the oxidation state IV, to the "second plutonium cycle" to complete the decontamination of this plutonium vis-à-vis the fission products that may still be present in this aqueous phase; the aqueous phase resulting from the "second washing U", which comprises decontaminated neptunium in uranium and plutonium and which can be removed from the cycle; - the aqueous phase resulting from the "U-stripping", which includes uranium (VI) decontaminated with plutonium and neptunium and which may be sent to a unit for converting uranium into uranium oxide suitable for use in the manufacture of new nuclear fuels, provided that the decontamination of this uranium with respect to the fission products is sufficient; and the organic phase resulting from the "U-stripping", which can be directed to a washing and regeneration unit of the organic phases. A second example of implementation of the process of the invention, in which the latter results from the introduction of an "a-complexing barrier" in the first purification cycle of the PUREX process illustrated in FIG. 1 in order to decontaminate uranium (VI) in neptunium (IV) and plutonium (IV) during the partition of uranium and plutonium, is illustrated in FIG. 3. In this example, the process of the invention differs from that of which has just been described in that the partitioning step does not include a "dam Pu", the latter being replaced by the "dam a-complexant". Also, the organic phase resulting from the "Pu desextraction", which includes uranium (VI), neptunium (IV) and plutonium (IV) (the latter being in the form of traces), is it directly subjected to an operation, called "Np / Pu desextraction", which aims to extract the neptunium (IV) and the plutonium (IV) present in this organic phase, by contact with a nitric aqueous phase of low acidity, for example a aqueous solution of 0.2 to 3 M nitric acid, which comprises a diglycolamide, for example TEDGA at a concentration of 0.01 to 0.1 mol / l, and then separation of the two phases. The aqueous phase resulting from the "Np / Pu desextraction" is subjected to an operation, referred to as "second U-wash", which aims at removing from the aqueous phase resulting from this extraction the fraction of uranium which has been de-extracted in conjunction with the neptunium and plutonium, by bringing this aqueous phase into contact with an organic phase, also comprising TBP in solution in an organic diluent, and then separating the two phases.
[0018] The organic phase resulting from the "Np / Pu desextraction" is itself subjected to an operation, called "U-desextraction", which aims to extract the uranium from this organic phase, by contacting this organic phase with a phase very dilute aqueous nitric acid, for example an aqueous solution of nitric acid 0.005 to 0.05 M, and then separation of the two phases.
[0019] Here again, at the end of the partitioning step, four phases are obtained, namely: the aqueous phase resulting from the "first washing U", which comprises plutonium (III) decontaminated with uranium and with neptunium and which can be directed, after an oxidation operation (not shown in Figure 3) to bring this plutonium to the oxidation state IV, to the "second plutonium cycle" to complete the decontamination of this plutonium vis- with respect to fission products that may still be present in this aqueous phase; the aqueous phase resulting from the "second washing U", which comprises uranium decontaminated neptunium (IV) as well as traces of plutonium (IV) and which is directed either towards the extractor where the "coextraction U" takes place; Pu "or to the extractor where the" complementary co-extraction U / Pu "takes place to recover traces of plutonium that includes; - the aqueous phase resulting from the "U-stripping", which includes uranium (VI) decontaminated with plutonium and neptunium and which may be sent to a unit for converting uranium into uranium oxide suitable for use in the manufacture of new nuclear fuels, provided that the decontamination of this uranium with respect to the fission products is sufficient; and the organic phase resulting from the "U-stripping", which can be directed to a washing and regeneration unit of the organic phases.
[0020] Reference is now made to FIG. 4 which represents a third example of implementation of the process of the invention, in which the latter results from the introduction of an "a-complexing barrier" in the first purification cycle of the COEXTM process as illustrated in Figures 1 and 4 of reference [1] to decontaminate uranium (VI) to neptunium (IV) during the partition of uranium and plutonium. In this example, the "a-complexing dam" is used in addition to the "dam Pu". The first purification cycle of the COEXTM process comprises, first of all, a step of decontaminating uranium and plutonium into fission products, americium and curium, which is carried out in the same manner as in the PUREX process. Thus, in the present example, the "U / Pu coextraction", "PF wash", "Tc wash" and "U / Pu complementary coextraction" operations previously described, with the production of an organic phase, are found again. , which is loaded with uranium (VI), plutonium (IV) but also with neptunium (VI).
[0021] As in the first cycle of the COEXTM process, this organic phase is directed to an area at which a stage of partitioning uranium and plutonium into two aqueous phases is carried out. However, this partitioning step is carried out differently from that illustrated in Figures 1 and 4 of reference [1] since it comprises an "a-complexing barrier" between the "dam Pu" and "U-stripping". Also, as can be seen in FIG. 4, the partitioning step comprises: an operation, called "Pu / Uextraction", which aims to extract from the organic phase resulting from the "Tc wash" the plutonium (IV) and a fraction of the uranium (VI) present in this phase, by bringing this organic phase into contact with an aqueous phase of weak acidity, for example a 0.05 to 2 M nitric acid solution, comprising, on the one hand, a reducing agent, for example uranous nitrate, and, on the other hand, an anti-nitrous agent, for example hydrazinium nitrate, and then separating the two phases; an operation, called "Pu dam", which aims to complete the extraction of plutonium (IV) by contacting the organic phase resulting from the "Pu / U desextraction" with a nitric aqueous phase of low acidity, for example a solution of 0.05 to 2 M nitric acid, comprising the same reducing agent and the same anti-nitrous agent as those used for the "Pu / U desextraction", then separation of the two phases; an operation, called "Np wash", which aims at removing from the aqueous phase resulting from the "Pu / U desextraction" the fraction of neptunium (IV) having been desextracted jointly with the plutonium and the uranium, by putting in contact this phase with an organic phase comprising TBP in solution at about 30% (v / v) in an organic diluent, then separation of the two phases; an operation, called "Np desextraction", which aims to extract the neptunium (IV) present in the organic phase resulting from the "Pu dam", by contacting this organic phase with a nitric aqueous phase of low acidity, for example an aqueous solution of 0.2 to 3 M nitric acid, which comprises a diglycolamide, for example TEDGA at a concentration of 0.01 to 0.1 mol / l, and then separation of the two phases; an operation, called "washing U", which aims to remove the aqueous phase resulting from the "Np desextraction" fraction of uranium that has been dextracted together with neptunium, by contacting this aqueous phase with an organic phase comprising also TBP in solution at approximately 30% (v / v) in an organic diluent, then separation of the two phases; and an operation, called "U-stripping", which aims to extract the uranium from the organic phase resulting from the "Np-stripping", by contacting this organic phase with a very dilute aqueous nitric phase, for example an aqueous solution. of nitric acid 0.005 to 0.05 M, then separation of the two phases. Four phases are thus obtained, namely: the aqueous phase resulting from the "washing Np", which comprises plutonium (III) and uranium (VI and optionally IV) decontaminated in neptunium and which can be directed, after an operation of oxidation (not shown in FIG. 4) making it possible to reduce the plutonium (III) to the oxidation state IV and, if applicable, the uranium (IV) to the oxidation state VI, towards the "Plutonium / uranium second cycle" with a view to perfecting the decontamination of this plutonium and this uranium with respect to the fission products likely to be still present in this aqueous phase; the aqueous phase resulting from the "washing U", which comprises neptunium (IV) decontaminated with uranium and plutonium and which can be removed from the cycle; - the aqueous phase resulting from the "U-stripping", which includes uranium (VI) decontaminated with plutonium and neptunium and which may be sent to a unit for converting uranium into uranium oxide suitable for use in the manufacture of new nuclear fuels, provided that the decontamination of this uranium with respect to the fission products is sufficient; and the organic phase resulting from the "U-stripping", which can be directed to a washing and regeneration unit of the organic phases.
[0022] A fourth example of implementation of the process of the invention, in which the latter results from the introduction of an "a-complexing barrier" in the first purification cycle of the COEXTM process as illustrated in FIGS. 4 of the reference [1] in order to decontaminate the uranium (VI) in neptunium (IV) and plutonium (IV) during the partition, is illustrated in FIG. 5. In this example, the process of the invention differs therefore of that which has just been described in that the partition step does not include a "dam Pu", the latter being replaced by the "dam a-complexant". Also, the organic phase resulting from the "Pu / U desextraction", which includes uranium (VI), neptunium (IV) and plutonium (IV) (the latter being in the form of traces), is it is directly subjected to an operation, called "Np / Pu desextraction", which aims to extract the neptunium (IV) and the plutonium (IV) present in this organic phase, by contact with a nitric aqueous phase of low acidity, by example an aqueous solution of 0.2 to 3 M nitric acid, which comprises a diglycolamide, for example TEDGA at a concentration of 0.01 to 1 mol / L, and then separation of the two phases. The aqueous phase resulting from the "Np / Pu desextraction" is subjected to an operation, called "washing U", which aims to remove from the aqueous phase resulting from this extraction the uranium fraction having been desextracted together with the neptunium and the plutonium, by contacting this aqueous phase with an organic phase, also comprising TBP in solution in an organic diluent, while the organic phase resulting from the "Np / Pu desextraction" is subjected to an operation, called "U-extraction". Which aims to extract the uranium from this organic phase by contacting this organic phase with a very dilute aqueous nitric phase, for example an aqueous solution of nitric acid 0.005 to 0.05 M, and then separating the two phases. Here again, at the end of the partitioning stage, four phases are obtained, namely: the aqueous phase resulting from the "washing Np", which comprises plutonium (III) and uranium (VI and optionally IV) decontaminated in neptunium and which can be directed after an oxidation operation (not shown in FIG. 5) making it possible to reduce the plutonium (III) to the oxidation state IV and, if appropriate, the uranium (IV) in the oxidation state VI, towards the "second plutonium / uranium cycle" in order to perfect the decontamination of this plutonium and this uranium with respect to the fission products likely to be still present in this aqueous phase; the aqueous phase resulting from the "washing U", which comprises decontaminated neptunium (IV) in uranium as well as traces of plutonium (IV) and which is directed either towards the extractor where the "U / Pu coextraction" takes place Or to the extractor where the "complementary co-extraction U / Pu" takes place to recover traces of plutonium that it comprises; - the aqueous phase resulting from the "U-stripping", which includes uranium (VI) decontaminated with plutonium and neptunium and which may be sent to a unit for converting uranium into uranium oxide suitable for use in the manufacture of new nuclear fuels, provided that the decontamination of this uranium with respect to the fission products is sufficient; and the organic phase resulting from the "U-stripping", which can be directed to a washing and regeneration unit of the organic phases. The invention is not limited to the embodiments that have just been described.
[0023] In particular, it is quite possible for two successive operations presented in FIGS. 2 to 5 to take place in two different multi-stage extractors to be made in the same multi-stage extractor, a part of the extractor then being devolved to the unfolding of the first operation and the other part of the extractor being devolved to the conduct of the second operation.
[0024] The following examples correspond to experimental tests which made it possible to validate the process of the invention. These tests are carried out using TEDGA as diglycolamide.
[0025] EXAMPLE 1 Experimental Tests in Test Tubes 1) Thermodynamic equilibrium study between the organic and aqueous phases: In these tests, a 30% (v / v) solution of TBP in 30% (v / v) TBP was used as the organic phase to be treated. TPH, which is derived from the mixture of concentrated and elemental organic solutions of uranium (VI), neptunium 237 in the state of oxidation IV and plutonium (IV), aiming at the following concentrations: 80 g / L of U (VI), 70 mg / L Np (IV) and 10 mg / L Pu (IV). These concentrations correspond to those typically exhibited by an organic phase at the end of the "Pu extraction" operation of the PUREX process illustrated in FIG. 1, except for the plutonium which is introduced in excess to determine the decontamination factors. in plutonium, noted FDpii, with better accuracy. In addition, a tracer, namely neptunium 239, was added to the organic Np (IV) solution in order to measure neptunium decontamination by spectrometry y. In addition, aqueous solutions used are aqueous solutions which are derived from the mixture of concentrated and elemental aqueous solutions of uranium (VI), nitric acid and TEDGA, in order to simulate an aqueous phase as obtained from equilibrium with the organic phase preceding the target acidity except Np, Pu and TEDGA. These aqueous solutions comprise 40 g / l of U (VI), 1 mol / l of HNO3 and an increasing concentration of TEDGA, ranging from 0 mol / l to 0.05 mol / l. Each aqueous phase is contacted in a test tube with an equivalent volume of organic phase (0 / A = 1) and the tube is allowed to vibrate for 30 minutes at room temperature (-25 ° C.). Then the phases in contact are separated and analyzed by spectrometry y and a. Table I below presents the values of the distribution coefficients of neptunium 237, neptunium 239 and plutonium, as well as the values of the decontamination factors for uranium in these elements, as determined from the results of these analyzes. , depending on the concentration of TEDGA aqueous phases used.
[0026] Table I [TEDGA] DNp-237 FDNp-237 DNp-239 FDNp-239 Dpu FDpu (M01 / 0 0 0.139 10 0.112 10 0.65 2.5 0.005 0.097 10 0.1 11 - - 0.01 0.006 165 0.003 304 - - 0.03 0.003 371 0.002 633 0.0125 81 0.05 0.008 131 - - 0.0108 92 This table shows that a TEDGA concentration of 0.005 mol / L leads, for neptunium, to distribution coefficients and decontamination factors that are not significantly different from those obtained in the absence of TEDGA, which suggests that this concentration is too low to obtain a complexation of neptunium by this ligand, however, from 0.01 mol / L of TEDGA, the decontamination factors of uranium in neptunium increase significantly to reach a value greater than 300 at this concentration 2) Kinetic study: In these tests, a TBP solution is used as the organic phase to be treated. at 30% (v / v) in TPH, which includes, as used in point 1) above, 80 g / L of uranium (VI) , 70 mg / L of neptunium (IV) and 10 mg / L of plutonium (IV), but which additionally comprises 50 mg / l of dibutylphosphoric acid (HDBP), which is the main degradation product of TBP, and 1 g / L of uranium (IV), so as to be as close as possible to the composition of the organic phase which is obtained at the end of the "Pu extraction" operation of the PUREX process illustrated in FIG. as regards the plutonium which, again, is introduced in excess.
[0027] HDBP is a compound that is known to slow down the kinetics of plutonium de-extraction. As for the U (IV), it will, as actinide (IV) be complexed by TEDGA and reduce the amount of TEDGA available to complex plutonium and neptunium.
[0028] As before, this organic phase is derived from the mixture of concentrated and elemental organic solutions of U (VI), Np (IV), Pu (IV), HDBP and U (IV). 239Np was also added to the organic Np (IV) solution to measure neptunium decontamination by y spectrometry.
[0029] As aqueous phase, an aqueous solution is used which, as previously, is obtained from the mixture of concentrated and elemental aqueous solutions of uranium (VI), nitric acid and TEDGA, in order to simulate an aqueous phase as obtained from the balance with the organic phase above to the target acidity except Np, Pu and TEDGA. This aqueous solution comprises 40 g / l of U (VI), 1 mol / l of HNO3 and 0.03 mol / l of TEDGA. This aqueous phase is contacted in a 25 mL jacketed glass cell, thermostated at 25 ° C, with vortex and vortex blade agitation (2000 rpm), with an equivalent volume of organic phase ( 0 / A = 1).
[0030] Samples are taken at 1, 3, 5, 7, 15 and 30 minutes after contacting the aqueous and organic phases in order to follow the kinetics of decontamination of the organic phase in neptunium and plutonium. For each sample taken, the phases in contact are separated and analyzed by spectrometry y and a.
[0031] Table II below presents the results of the analyzes carried out on the aqueous phase of the samples. It indicates the activities of neptunium 239 and plutonium (expressed in KBq per liter of aqueous phase) as measured by spectrometry y for neptunium 239 and by a spectrometry for plutonium, as well as plutonium concentrations (expressed in mg / L ) as measured by spectrometry a, as a function of the contact time of the aqueous and organic phases.
[0032] Table II Aqueous phase Contact time [Np-239] [Pu] [Pu] (min) (KBq / L) (KBq / L) (mg / L) 1,600 3108 9.9 3,619 3268 10.4 637 3321 10.6 7 678 4296 13.7 15 605 3579 11.4 30 689 3559 11.3 Table III below presents, him, the results of the analyzes carried out on the organic phase of the samples. It indicates the activities of neptunium 239 (expressed in KBq per liter of organic phase) as determined by y spectrometry, the values of the distribution coefficients of neptunium 239 and the values of the decontamination factors of uranium in neptunium 239, as a function of the contact time of the aqueous and organic phases. Table III Organic phase Contact time [Np-239] DNp-239 FDNp-239 (min) (KBq / L) 0 618 3 14 2.3.10-3 441 5 7 1.1.10-3 866 7 13 1.9.10- These tables show that the values of the decontamination factor of uranium in neptunium 239 are greater than 300 after a single contact and 3 minutes of contact between the aqueous and organic phase. The kinetics of desextraction of neptunium is rapid and not limiting, even in the presence of 50 mg / l of HDBP and 1 g / l of U (IV). EXAMPLE 2 Experimental Tests in Mixer-Decanter Batteries Experimental tests for the implementation of an "a-complexing barrier" are carried out using two mixer-decanter batteries of 8 stages each, according to the diagram shown in FIG. .
[0033] The organic phase to be treated comprises: 82 g / l of uranium (VI), 61 mg / l of neptunium (IV), 20 mg / l of plutonium (IV), 50 mg / l of HDBP and 30% (v / v) TBP in TPH. 239Np was added to this phase to measure neptunium decontamination by y spectrometry. The first mixer-settler battery is dedicated to the "a-complexing barrier" and is divided into two zones of 4 stages each: a first zone, called "Np / Pu desextraction", for the desextraction of neptunium (IV) and plutonium (IV) and a second zone, called "washing U", for washing the aqueous phase resulting from this extraction. The second battery of mixer-settlers is entirely dedicated to the uranium (VI) extraction of the organic phase from the first battery of settling mixers. It is therefore called "U-stripping". As can be seen in FIG. 6, the feed solutions of the first mixer-settler battery are: the organic phase to be treated which is introduced at stage 5 at the nominal flow rate of 60 ml / h; an aqueous phase comprising 1 mol / L of nitric acid and 0.03 mol / L of TEDGA, which is introduced at stage 8, at the nominal flow rate of 7 mL / h, and at stage 4, at the nominal flow rate 5 mL / h; and an organic phase which comprises 30% (v / v) of TBP diluted in TPH and 0.01 mol / l of nitrous acid to promote the oxidation of the uranium (IV) present in the organic phase to be treated ; this organic phase is introduced in stage 1, at the nominal flow rate of 12 ml / h. The second battery of mixer-settlers is fed with the first, the organic phase resulting from the "Np / Pu desextraction" which is introduced to the stage 1 and, secondly, with a solution aqueous solution comprising 0.02 mol / L of nitric acid, which is introduced at stage 8, at the nominal flow rate of 90 ml / h. The temperature in the first mixer-settler battery is 28 ° C while the temperature in the second battery is 40 ° C. Under these conditions, the stationary equilibrium state is reached after about 6 hours. The activity of neptunium 239 is measured spectrometrically in the organic phase to be treated and in the aqueous phases resulting from the "washing U" and the "U-stripping". Similarly, the concentrations of uranium (VI), neptunium (IV) and plutonium (IV) are measured by X-Fluorescence or ICP-AES in each of these phases.
[0034] The results of these measurements are presented in Table IV below as well as the decontamination factors of uranium in neptunium on the one hand, and in plutonium on the other hand. Table IV Phase Aqueous phase FD U / Np organic aqueous phase from the end of the process "U wash" U "desextraction U (g / L) 82 0.14 49.94 Np (IV) (mg / L) ) 61.4 355.3 <0.1> 374 239 N p (KBq / L) 3 000 15 010 0.5 3654 Pu (mg / L) 20 103 <0.1> 122 This table shows that a factor of neptunium uranium near 3650, more than 10 times higher than that required by the most stringent specification that has been defined to date by the UNIREP standards for the decontamination of uranium in neptunium and which is of 308. The introduction of an "a-complexing barrier" in a PUREX or COEXTM process, according to the diagram shown in FIG. 6, thus makes it possible to overcome the need to carry out the "second uranium cycle", provided that the decontamination of the uranium with respect to the fission products is, moreover, sufficient. REFERENCES CITED [1] WO 2007/135178 [2] WO 2005/052950 [3] Sasaki et al., Analytical Sciences 2007, 23 (6), 727

权利要求:
Claims (15)
[0001]
REVENDICATIONS1. A method of treating spent nuclear fuel, which comprises decontaminating uranium (VI) in one or more actinides (IV), which decontamination comprises at least one actinide (IV) or actinide ( IV) of an organic phase, immiscible with water and in which uranium (VI) and actinide (IV) or actinides (IV) are present, by contacting the organic phase with a phase aqueous composition comprising nitric acid and at least one complexing agent which more strongly complexes actinides (IV) than uranium (VI), then separation of the organic phase from the aqueous phase, and which is characterized in that said less a complexing agent is a diglycolamide.
[0002]
2. Method according to claim 1, characterized in that the diglycolamide is chosen from N, N, N ', N'-tetramethyldiglycolamide, N, N, N', N'-tetraethyl diglycolamide, N, N, N, N'-tetrapropyl diglycolamide and N, N-dipropyl diglycol amine acid.
[0003]
3. Method according to claim 2, characterized in that the diglycolamide is N, N, N ', N'-tetraethyldiglycolamide.
[0004]
4. Method according to any one of claims 1 to 3, characterized in that the aqueous phase comprises from 0.01 to 0.1 mol / L of diglycolamide.
[0005]
5. Method according to any one of claims 1 to 4, characterized in that the aqueous phase comprises from 0.2 to 3 mol / L of nitric acid.
[0006]
6. Method according to any one of claims 1 to 5, characterized in that the decontamination of uranium (VI) into actinide (IV) or actinides (IV) further comprises a washing operation of the phase aqueous solution resulting from the extraction of actinide (IV) or actinides (IV), by bringing this nitric phase-analyzer into contact with an organic phase comprising an extractant of uranium (VI), and then separating the organic phase from the aqueous phase.
[0007]
7. Process according to claim 6, characterized in that the extractant is tri-n-butyl phosphate.
[0008]
8. Process according to any one of Claims 1 to 7, characterized in that the actinide (IV) or the actinides (IV) are chosen from neptunium (IV), plutonium (IV) and thorium (IV). .
[0009]
9. Method according to any one of claims 1 to 8, characterized in that the decontamination of uranium (VI) into one or more actinides (IV) is a decontamination of uranium (VI) in neptunium (IV) .
[0010]
10. Method according to claim 9, characterized in that it comprises: a) a decontamination step of uranium and plutonium present in an aqueous phase resulting from the dissolution of a spent nuclear fuel in nitric acid , with respect to the actinides (III) and fission products also present in this phase, which step comprises: a) at least one co-extraction operation of the uranium, in the oxidation state VI, and plutonium, in the IV oxidation state, of the aqueous phase, by bringing this aqueous phase into contact with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separating the organic phase the aqueous phase; and a2) at least one washing operation of the organic phase derived from ai) to remove from this aqueous phase the fraction of fission products that have been extracted during ai), by contacting said organic phase with an aqueous phase comprising nitric acid, and then separating the organic phase from the aqueous phase; by means of which an organic phase is obtained which comprises uranium (VI), plutonium (IV) and neptunium (VI), b) a step of partitioning the uranium and plutonium present in the organic phase resulting from the step a) in two aqueous phases, a first aqueous phase comprising plutonium decontaminated with uranium and neptunium and a second aqueous phase comprising decontaminated uranium with plutonium and with neptunium, which step comprises: b1) a process for removing the plutonium present in the organic phase resulting from stage a), the plutonium being extracted in the oxidation state III by contacting the organic phase resulting from stage a) with an aqueous phase comprising acid Nitric, a reducing agent that reduces plutonium (IV) to plutonium (III) and neptunium (VI) to neptunium (IV) without reducing uranium (VI), and an anti-nitrous agent, and then separating the organic phase the aqueous phase; b2) a washing operation of the organic phase resulting from b1) to remove from this organic phase the plutonium fraction that has not been de-extracted during b1), by bringing said organic phase into contact with an aqueous phase comprising nitric acid, the same reducing agent and the same anti-nitrous agent as those used for the plutonium desextraction operation, and then separating the organic phase from the aqueous phase; b3) a washing operation of the aqueous phase resulting from b1) to remove from this aqueous phase the fraction of uranium (VI) and neptunium (IV) which has been de-extracted during b1), by contacting said phase aqueous solution with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separating the organic phase from the aqueous phase; b4) the decontamination of uranium (VI) into neptunium (IV), this decontamination comprising a neptunium (IV) desextraction operation present in the organic phase resulting from b2), by bringing this organic phase into contact with a phase aqueous solution comprising nitric acid and diglycolamide, and then separating the organic phase from the aqueous phase, and a washing operation of the aqueous phase resulting from the neptunium (IV) de-extraction operation, by bringing this aqueous phase with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separation of the organic phase from the aqueous phase; andb5) a uranium (VI) de-extraction operation present in the organic phase resulting from the operation of the neptunium (IV) desextraction of b4), by bringing this organic phase into contact with an aqueous phase comprising nitric acid, and then separation of the organic phase from the aqueous phase.
[0011]
11. The method of claim 9, characterized in that it comprises: a) a decontamination step of uranium and plutonium present in an aqueous phase resulting from the dissolution of a spent nuclear fuel in nitric acid , with respect to the actinides (III) and fission products also present in this phase, which step comprises: a) at least one co-extraction operation of the uranium, in the oxidation state VI, and plutonium, in the IV oxidation state, of the aqueous phase by bringing this aqueous phase into contact with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separating the organic phase from the aqueous phase; and a2) at least one washing operation of the organic phase resulting from a1) in order to remove from this aqueous phase the fraction of fission products that has been extracted during step a), by bringing this organic phase into contact with an aqueous phase comprising nitric acid, and then separating the organic phase from the aqueous phase; whereby an organic phase is obtained which comprises uranium (VI), plutonium (IV) and neptunium (VI); b) a step of partitioning the uranium and plutonium present in the organic phase resulting from step a) into two aqueous phases, a first aqueous phase comprising plutonium and uranium decontaminated in neptunium and a second aqueous phase; comprising decontaminated uranium with plutonium and neptunium, which step comprises: b1) a process for the extraction of plutonium and a fraction of the uranium present in the organic phase resulting from step a), the plutonium being extracted in the oxidation state III by contacting the organic phase resulting from step a) with an aqueous phase comprising nitric acid, a reducing agent which reduces the plutonium (IV) to plutonium (III) and the neptunium (VI) to neptunium (IV) without reducing uranium (VI), and an anti-nitrous agent, and then separating the organic phase from the aqueous phase; b2) a washing operation of the organic phase resulting from b1) to remove from this organic phase the plutonium fraction that has not been de-extracted during b1), by bringing said organic phase into contact with an aqueous phase comprising nitric acid, the same reducing agent and the same anti-nitrous agent as those used for the plutonium desextraction operation, and then separating the organic phase from the aqueous phase; b3) a washing operation of the aqueous phase from b1) to remove from this aqueous phase the fraction of neptunium (IV) having been deextracted during b1), by contacting this aqueous phase with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separating the organic phase from the aqueous phase; b4) the decontamination of uranium (VI) into neptunium (IV), this decontamination comprising a neptunium (IV) desextraction operation present in the organic phase resulting from b2), by bringing this organic phase into contact with a phase aqueous composition comprising nitric acid and diglycolamide, and then separation of the organic phase from the aqueous phase, and a washing operation of the aqueous phase resulting from the neptunium (IV) desextraction operation by contacting this phase aqueous solution with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separating the organic phase from the aqueous phase; and b5) a uranium extraction operation present in the organic phase resulting from the neptunium (IV) dextraction operation of b4), by bringing this organic phase into contact with an aqueous phase comprising nitric acid; and then separating the organic phase from the aqueous phase.
[0012]
12. Process according to claim 8, characterized in that the step of decontaminating uranium (VI) in one or more actinides (IV) is a step of decontaminating the uranium (VI) in neptunium (IV) and in plutonium (IV).
[0013]
13. The method of claim 12, characterized in that it comprises: a) a decontamination step of uranium and plutonium present in an aqueous phase resulting from the dissolution of a spent nuclear fuel in nitric acid , with respect to the actinides (III) and fission products also present in this phase, which step comprises: a) at least one co-extraction operation of the uranium, in the oxidation state VI, and plutonium, in the IV oxidation state, of the aqueous phase, by bringing this aqueous phase into contact with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separating the organic phase the aqueous phase; and a2) at least one washing operation of the organic phase resulting from ai), by contacting this organic phase with an aqueous phase comprising nitric acid, and then separating the organic phase from the aqueous phase; whereby an organic phase is obtained which comprises uranium (VI), plutonium (IV) and neptunium (IV); b) a step of partitioning the uranium and plutonium present in the organic phase resulting from step a) into two aqueous phases, a first aqueous phase comprising decontaminated uranium and neptunium plutonium and a second aqueous phase comprising decontaminated uranium to plutonium and neptunium, which step comprises: b1) a plutonium extraction operation in the organic phase resulting from step a), the plutonium being extracted in the oxidation state III by means of contacting the organic phase resulting from stage a) with an aqueous phase comprising nitric acid, a reducing agent which reduces plutonium (IV) enplutonium (III) and neptunium (VI) to neptunium (IV) without reducing uranium (VI), and an anti-nitrous agent, and then separating the organic phase from the aqueous phase; b2) a washing operation of the aqueous phase from b1) to remove from this phase the fraction of uranium (VI) and neptunium (IV) having been de-extracted during b1), by contacting this aqueous phase with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separating the organic phase from the aqueous phase; b3) the decontamination of the uranium (VI) in neptunium (IV) and in plutonium (IV), this decontamination comprising a process for the extraction of neptunium (IV) and plutonium (IV) present in the organic phase resulting from b1) by bringing this organic phase into contact with an aqueous phase comprising nitric acid and diglycolamide, and then separating the organic phase from the aqueous phase, and washing the aqueous phase resulting from the de-extraction operation. neptunium (IV) by contacting this aqueous phase with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separating the organic phase from the aqueous phase; and b4) a uranium extraction operation present in the organic phase resulting from the operation of the extraction of neptunium (IV) and plutonium (IV) from b3), by contacting this organic phase with an aqueous phase comprising nitric acid, and then separating the organic phase from the aqueous phase.
[0014]
14. Process according to claim 12, characterized in that it comprises: a) a step of decontaminating the uranium and plutonium present in an aqueous phase resulting from the dissolution of a spent nuclear fuel in nitric acid , with respect to the actinides (III) and fission products also present in this phase, which step comprises: a) at least one co-extraction operation of the uranium, in the oxidation state VI, and plutonium, in the IV oxidation state, of the aqueous phase by contacting this aqueous phase with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separating the organic phase from the organic phase. aqueous phase ; and a2) at least one washing operation of the organic phase resulting from a1), by bringing this organic phase into contact with an aqueous phase comprising nitric acid, and then separating the organic phase from the aqueous phase; whereby an organic phase is obtained which comprises uranium (VI), plutonium (IV) and neptunium (VI); b) a step of partitioning the uranium and plutonium present in the organic phase resulting from step a) into two aqueous phases, a first aqueous phase comprising plutonium and uranium decontaminated in neptunium and a second aqueous phase; comprising decontaminated uranium in neptunium and plutonium, which step comprises: b1) an operation for the desextraction of the plutonium and a fraction of the uranium present in the organic phase resulting from step a), the plutonium being de-extracted in the oxidation state III by contacting the organic phase resulting from step a) with an aqueous phase comprising nitric acid, a reducing agent which reduces the plutonium (IV) to plutonium (III) and neptunium (VI) to neptunium (IV) without reducing uranium (VI), and an anti-nitrous agent, and then separating the organic phase from the aqueous phase; b2) a washing operation of the aqueous phase from b1) to remove from this aqueous phase the fraction of neptunium (IV) having been deextracted during b1), by contacting said aqueous phase with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separating the organic phase from the aqueous phase; b3) the decontamination of the uranium (VI) in neptunium (IV) and in plutonium (IV), this decontamination comprising a process for the extraction of neptunium (IV) and plutonium (IV) present in the organic phase resulting from b1) by bringing this organic phase into contact with an aqueous phase comprising acidenitric acid and diglycolamide, and then separating the organic phase from the aqueous phase, and washing the aqueous phase resulting from the desextraction operation of the neptunium (IV) by contacting this aqueous phase with an organic phase comprising tri-n-butyl phosphate in an organic diluent, and then separating the organic phase from the aqueous phase; and b4) a uranium extraction operation present in the organic phase resulting from the neptunium (IV) de-extraction operation of b3), by bringing this organic phase into contact with an aqueous phase comprising nitric acid and then separating the organic phase from the aqueous phase.
[0015]
15. Process according to any one of Claims 10, 11, 13 and 14, characterized in that the aqueous phase comprising nitric acid and diglycolamide comprises from 0.2 to 3 mol / L of nitric acid and of 0.01 to 0.1 mol / L of N, N, N ', N' - tetraethyl diglyl colamide.

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EP3084773A1|2016-10-26|

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法律状态:
2015-12-31| PLFP| Fee payment|Year of fee payment: 3 |

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2016-12-29| PLFP| Fee payment|Year of fee payment: 4 |

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2018-01-02| PLFP| Fee payment|Year of fee payment: 5 |

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2019-09-27| ST| Notification of lapse|Effective date: 20190906 |

优先权:

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申请号 | 申请日 | 专利标题

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FR1363251A|FR3015760B1|2013-12-20|2013-12-20|PROCESS FOR TREATING A USE NUCLEAR FUEL COMPRISING A DECONTAMINATION STEP OF URANIUMIN AT LEAST ONE ACTINIDEBY COMPLEXATION OF THIS ACTINIDE |FR1363251A| FR3015760B1|2013-12-20|2013-12-20|PROCESS FOR TREATING A USE NUCLEAR FUEL COMPRISING A DECONTAMINATION STEP OF URANIUMIN AT LEAST ONE ACTINIDEBY COMPLEXATION OF THIS ACTINIDE |

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JP2016541413A| JP6671286B2|2013-12-20|2014-12-18|A method for treating spent nuclear fuel, comprising the step of decontaminating uraniumby complexing at least one actinidewith this actinide |

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EP14815711.8A| EP3084773B1|2013-12-20|2014-12-18|Method for processing spent nuclear fuel comprising a step of decontaminating the uraniuminto at least one actinideby complexing this actinide |

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RU2016129581A| RU2663882C1|2013-12-20|2014-12-18|Method for recycling nuclear waste, including uraniumpurification from at least one actinideby producing actinidecomplex|

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CN201480070061.3A| CN105849818B|2013-12-20|2014-12-18|Including the method by the way that processing spent nuclear fuel of at least one actinidesfrom the actinidesthe step of purification uraniumis complexed|

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US15/104,154| US10210958B2|2013-12-20|2014-12-18|Method for processing spent nuclear fuel comprising a step for decontaminating uraniumfrom at least one actinideby complexing this actinide |

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PCT/EP2014/078453| WO2015091791A1|2013-12-20|2014-12-18|Method for processing spent nuclear fuel comprising a step of decontaminating the uraniuminto at least one actinideby complexing this actinide |