Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D11/00—Solvent extraction
  • B01D11/04—Solvent extraction of solutions which are liquid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D11/00—Solvent extraction
  • B01D11/04—Solvent extraction of solutions which are liquid
  • B01D11/0446—Juxtaposition of mixers-settlers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D11/00—Solvent extraction
  • B01D11/04—Solvent extraction of solutions which are liquid
  • B01D11/0488—Flow sheets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D11/00—Solvent extraction
  • B01D11/04—Solvent extraction of solutions which are liquid
  • B01D11/0492—Applications, solvents used
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D59/00—Separation of different isotopes of the same chemical element
  • B01D59/22—Separation by extracting
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B60/00—Obtaining metals of atomic number 87 or higher, i.e. radioactive metals
  • C22B60/02—Obtaining thorium, uranium, or other actinides
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C19/00—Arrangements for treating, for handling, or for facilitating the handling of, fuel or other materials which are used within the reactor, e.g. within its pressure vessel
  • G21C19/42—Reprocessing of irradiated fuel
  • G21C19/44—Reprocessing of irradiated fuel of irradiated solid fuel
  • G21C19/46—Aqueous processes, e.g. by using organic extraction means, including the regeneration of these means
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
  • G21F9/04—Treating liquids
  • G21F9/06—Processing
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E30/00—Energy generation of nuclear origin
  • Y02E30/30—Nuclear fission reactors
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies

Definitions

• the present invention relates to a method for very efficiently separating a chemical element from uranium (VI) from a nitric aqueous phase, in a uranium extraction cycle, when this chemical element is present in this aqueous phase at a concentration lower than that of the uranium (VI), or even in the form of traces, and that it is, moreover, less extractable by the extractant used in this extraction cycle than is the uranium (VI).
• the chemical element can in particular be a tetravalent actinide such as neptunium or thorium 228 (which is a decay product of uranium 232), but the process according to the invention can also be applied to the separation of any other element chemical capable of being partially co-extracted with uranium from an acidic aqueous phase, in a uranium extraction cycle, such as zirconium.
• a tetravalent actinide such as neptunium or thorium 228 (which is a decay product of uranium 232)
• the process according to the invention can also be applied to the separation of any other element chemical capable of being partially co-extracted with uranium from an acidic aqueous phase, in a uranium extraction cycle, such as zirconium.
• the process according to the invention can in particular be implemented in the context of a process for the reprocessing of irradiated nuclear fuels, and in particular in the purification cycle of uranium called "second uranium cycle" of the PUREX process or of any other process derived from it, with the aim of facilitating the decontamination of uranium to a pollutant such as neptunium, either for the purpose of recovering a chemical element which is present in trace amounts in the concentrated aqueous stream of uranium, resulting from the first purification cycle of uranium.
• this process and which is likely to be valued - which is particularly the case of thorium 228 - these two objectives are, moreover, not exclusive of one another.
• the first purification cycle aims to jointly separate the uranium and plutonium from the fission products and then to partition these two elements into two streams.
• this first cycle begins with an operation consisting in co-extracting uranium and plutonium, the first at the oxidation state VI, the second at the oxidation degree IV, with a nitric aqueous phase that results from the dissolution a spent nuclear fuel in nitric acid and which is called, therefore, dissolution liquor.
• a water-immiscible organic phase which consists of an extractant having a high affinity for uranium (VI) and plutonium (IV), in this case the tri-n-butyl phosphate (hereinafter TBP), generally at 30% by volume in an organic diluent, generally a hydrocarbon such as hydrogenated tetrapropylene
• TPH n-dodecane or "odorless kerosene”. It is completed by a washing of the organic phase which is carried out by means of an aqueous nitric solution and which is intended to complete the decontamination of uranium and plutonium with respect to the fission products.
• the partition operation of uranium and plutonium is then carried out. It is based on a deliberate alteration of the degree of oxidation of plutonium (IV) which is brought to the trivalent state, where it is not very extractable by the TBP, to favor its passage in an aqueous nitric solution and thus to separate it from the uranium (VI) which remains in the organic phase. This reduction is carried out using a reducing agent, uranous nitrate, and an anti-nitrous agent, hydrazine, whose role is to stabilize both the uranous nitrate and the plutonium (III) by destruction of nitrous acid.
• neptunium present in the solution liquor is co-extracted, mainly in the form of neptunium (VI), with uranium and plutonium.
• thorium 228, which exists in aqueous solution only in the tetravalent state, is partially co-extracted with uranium and plutonium (Germain et al., Journal of Inorganic Nuclear Chemistry, 1970, vol. 32, pp 245-253).
• the neptunium (VI) is reduced by the uranous nitrate to neptunium (IV), a state in which it is extractable by TBP, although less than the degree of oxidation VI. It remains in the organic phase with uranium, just like a large part of thorium (IV).
• the uranium (VI) is extracted from the organic phase by means of an aqueous nitric solution and the tetravalent actinides which followed it during the previous operations (neptunium (IV), plutonium (IV ) and thorium (IV), these last two elements being present in the state of traces) are dextracted with him.
• aqueous effluent resulting from the desextraction of uranium is then subjected, after an intercycle concentration operation, to a second purification cycle called "second uranium cycle" to decontaminate the uranium with respect to neptunium.
• second uranium cycle a second purification cycle
• the inventors have therefore set themselves the goal of providing a process which makes it possible, in a uranium extraction cycle such as that practiced in the "second uranium cycle" of the PUREX process, to very efficiently separate a chemical element from Uranium (VI) from a nitric aqueous phase when this chemical element is present in this aqueous phase at a concentration less than that of the uranium (VI), or even at trace levels, and Moreover, it is less extractable by the extractant chosen to carry out this extraction cycle than is uranium (VI).
• the inventors have set a goal of providing a method which makes it possible to recover the chemical element in a concentrated and purified form in the case where this element is recoverable.
• a method for separating a chemical element from uranium (VI) from an aqueous nitric Al phase in a uranium extraction cycle comprising: a) a step for extracting uranium (VI), in which an aqueous phase circulates, at a flow rate Di, in a first extractor (10), against the current of an organic phase, immiscible with water and containing a extractant, and b) a step of washing the organic phase obtained at the end of step a) with an aqueous nitric phase A2, in which the organic phase circulates in a second extractor (11) against the current of the phase A2; in which the first and second extractors are connected to each other so that the aqueous phase which circulates in the first extractor is formed by the Al phase and the A2 phase obtained at the end of step b) ; and wherein, the chemical element being present in the Al phase at a concentration lower than that of the uranium (VI) and being
• the exact position of the withdrawal in the first extractor is chosen according to the main objective that has been set.
• a withdrawal upstream of the peak of accumulation of the chemical element in the organic phase will make it possible to obtain better decontamination of uranium with respect to this chemical element and vice versa, and will therefore be preferred in the case where the main objective is to decontaminate uranium with respect to a pollutant, while a withdrawal at the peak of accumulation of the chemical element in the organic phase will make it possible to obtain a maximum concentration of the chemical element in the part of withdrawn aqueous phase but at the cost of a greater contamination of this element by uranium, and will therefore be preferred in the case where we will seek essentially to recover this element for its recovery .
• the peak of accumulation of the chemical element in the organic phase is pronounced, or as strong as possible.
• steps a) and b) are preferably chosen so as to obtain:
• an extraction factor of the chemical element greater than 1 and, preferably, much greater than 1 in the part of the first extractor located upstream (in the direction of circulation of the organic phase) of the front uranium extraction, but less than 1 and, preferably, much less than 1 in the second extractor and in the part of the first extractor closest to its aqueous phase feed.
• the flow rate D 2 of the withdrawal represents a fraction of the flow Di such that the product of the concentration of the chemical element in the aqueous phase at the time of the withdrawal and the flow rate D 2 is equal to the flow of this element that enters the first extractor, so that the flows in and out of said element are balanced.
• the process according to the invention further comprises one or more steps of concentration and purification of the chemical element present in the part of aqueous phase withdrawn.
• the step Ci) is advantageously carried out by adding the withdrawn aqueous phase part to the phase A3 obtained at the end of step di) and by circulating the resulting aqueous stream in a third extractor, countercurrent to the organic phase.
• this process comprises a step C 2 ) comprising subjecting the withdrawn aqueous phase portion to one or more chromatographies on a stationary solid phase to concentrate and purify the chemical element present in that phase.
• the stationary solid phase is an ion exchange resin.
• the extractant present in the organic phases used in the steps may be any molecule known to have a particular affinity for uranium.
• a trialkyl phosphate and, in particular, tri-n-butyl phosphate which is the extractant of the PUREX process.
• it is preferably used at 30% v / v in an organic diluent, preferably a linear or branched dodecane such as hydrogenated n-dodecane or tetrapropylene.
• Al phase is preferably a nitric aqueous phase of high acidity, concentration of nitric acid of the order of 4 to 6 mol / L, in which case the aqueous nitric phases used for the washes (phases A2 and A3) are of low acidity, for example of concentration of nitric acid less than or equal to 2 mol / L .
• the method according to the invention makes it possible to avoid, on stopping the cycle, a pollution of the uranium by the chemical element: Indeed, it is sufficient to continue step a) by feeding the first decontaminated uranium extractor while continuing to withdraw a portion of the aqueous phase circulating in this extractor to reduce the accumulation of the chemical element without polluting the last batch of 'uranium.
• the chemical element is preferably a tetravalent actinide chosen from neptunium and thorium 228.
• the invention also relates to a process for reprocessing a spent nuclear fuel, which is characterized in that it implements a separation method as previously defined.
• the invention also relates to a uranium purification cycle of a PUREX process, which is characterized in that it comprises the implementation of a separation process as defined above, in which case the
• the chemical element to be separated from the uranium (VI) is preferably a tetravalent actinide selected from neptunium and thorium 228.
• FIG. 1A is a schematic diagram of an extraction cycle such that it can be used to decontaminate the uranium (VI) present in an aqueous nitric phase with respect to of a chemical element, less extractable than it, for example in the context of the "second uranium cycle" of a PUREX process;
• VI uranium
• FIG. 1B shows the concentration profiles [C org ] of the uranium (VI) (curve A) and of the chemical element (curve B) in the organic phase, as well as the acidity profile (curve C). of this phase, during the extraction cycle illustrated in Figure IA;
• FIG. 2 schematically illustrates an example of the first embodiment of
• FIG. 3 illustrates, schematically, an example of the second preferred embodiment of the method according to the invention.
• the extractors are symbolized by rectangles
• the organic phase flows are symbolized by a double line and this phase is called more simply "solvent”
• the aqueous streams are symbolized by a single line .
• FIG. 1A schematically represents an extraction cycle such that it can be used to decontaminate the uranium (VI) present in a nitric aqueous phase, referred to as the Al phase.
• a chemical element called element E, less extractable than it, for example in the context of the "second uranium cycle" of a PUREX process.
• the uranium (VI) is present at a high concentration, for example of the order of 400 g / L, while the element E, which is, for example, neptunium (IV) or thorium 228 (which is also tetravalent) is present at a much lower concentration, for example of the order of 1% or less of that of uranium, or even in trace amounts.
• the extraction cycle includes:
• an extraction step proper which aims at extracting uranium (VI) from phase Al by means of an organic phase which is immiscible with water and contains an extractant capable of extracting uranium and to a lesser degree, the element E, and
• A2 phase a nitric aqueous phase
• VI uranium
• the organic phase is, for example, composed of 30% v / v tri-n-butyl phosphate in a dodecane
• the A2 phase is, for example, an aqueous solution of acidity less than 2 mol / L of HNO 3 , for example of the order of 1 mol / L.
• these extraction and washing steps are carried out in two different extractors, respectively 10 and 11, which are preferably multi-stageed (of the mixer-settler or pulsed column type), which are connected to each other. to one another and in which the solvent and aqueous phases are circulated in countercurrent.
• the extractor 10 is therefore powered:
• FIG. 1B shows the concentration profiles [C org ] of uranium (curve A) and element E (curve B) in the organic phase, as well as the acid profile ( curve C) of this phase, over its entire path in the extractors 10 and 11.
• This figure shows that in the part of the extractor 10 situated upstream (in the direction of circulation of the organic phase) of the uranium extraction front which corresponds to the segment of the curve A which is between the f- z arrows and 3 -, an accumulation of nitric acid in the organic phase which promotes the passage of the element E in the organic phase and the formation of a peak of accumulation of this element in this organic phase (and, inseparably , also in the aqueous phase).
• the method according to the invention thus comprises two cycles of extraction, coupled to each other, namely: a first cycle, which is identical to that illustrated in FIG. 1A, except that a part of the aqueous phase circulating in the extractor 10 is withdrawn at the peak of accumulation of the element E in the organic phase or upstream (in the direction of circulation of the organic phase) of this peak, and
• An extraction step proper which aims at extracting the uranium (VI) present in the portion of aqueous phase withdrawn in the extractor 10 of this part of the aqueous phase, by means of an organic phase, which is advantageously same composition as that used in the first extraction cycle (TBP at 30% v / v in an organic diluent), and • a step of washing the organic phase with a nitric aqueous phase (called hereinafter phase A3), for example an aqueous solution of acidity less than 2 mol / l of HNO3, which aims to extract from the organic phase the fraction of element E which has been extracted with uranium (VI) at 'previous step.
• phase A3 a nitric aqueous phase
• the extraction and washing steps of this second cycle are carried out, like those of the first cycle, in two different extractors, respectively 12 and 13, which are connected to each other and to each other. wherein the solvent and aqueous phases are circulated countercurrently.
• FIG. 3 illustrates, schematically, an example of the second preferred embodiment of the method according to the invention, wherein the aqueous phase portion withdrawn into the extractor 10 is subjected to additional operations ion exchange resin chromatography to concentrate and purify the element E it contains, and which is particularly well suited to the case where the element E is in the trace state in the Al phase.
• the process comprises, first of all, an extraction cycle which is identical to that illustrated in FIG. 1A, except that part of the aqueous phase flowing in the extractor 10 is withdrawn at the peak accumulation of the element E in the organic phase or upstream (in the direction of circulation of the organic phase) of this peak.
• the withdrawn aqueous phase fraction is fed into a buffer tank 14 where it is stored before being conveyed to a column 15 filled with an ion exchange resin. Elution and then washing the resin with aqueous nitric phases makes it possible to recover at the outlet of the column E-element rich fractions and uranium-rich (VI) -rich fractions. These are sent to join phase Al before it is added to phase A2.

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• 2006
  • 2006-07-03 FR FR0652772A patent/FR2903025B1/fr not_active Expired - Fee Related
• 2007
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