EP0186677B1 - Device for conditioning radioactive waste comprised of mediumand /or long period actinides - Google Patents

Device for conditioning radioactive waste comprised of mediumand /or long period actinides Download PDF

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EP0186677B1
EP0186677B1 EP19850902571 EP85902571A EP0186677B1 EP 0186677 B1 EP0186677 B1 EP 0186677B1 EP 19850902571 EP19850902571 EP 19850902571 EP 85902571 A EP85902571 A EP 85902571A EP 0186677 B1 EP0186677 B1 EP 0186677B1
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elements
actinide
mixture
life
emitter
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German (de)
French (fr)
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EP0186677A1 (en
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Michel Beauvy
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique CEA
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21G—CONVERSION OF CHEMICAL ELEMENTS; RADIOACTIVE SOURCES
    • G21G1/00—Arrangements for converting chemical elements by electromagnetic radiation, corpuscular radiation or particle bombardment, e.g. producing radioactive isotopes
    • G21G1/04—Arrangements for converting chemical elements by electromagnetic radiation, corpuscular radiation or particle bombardment, e.g. producing radioactive isotopes outside nuclear reactors or particle accelerators
    • 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

Definitions

  • the present invention relates to a device for conditioning radioactive waste consisting essentially of actinides with a medium and / or long period.
  • the first solution consists in storing this waste in stable geological layers, after having introduced them into glass or resin matrices.
  • the second solution consists in transforming this waste in a nuclear reactor, by reaction of fission or transmutation into elements with much shorter period or into fissile isotopes usable in nuclear reactors.
  • the first solution requires a complex packaging infrastructure in glass or resin matrices.
  • the stability of these matrices is not guaranteed in the very long term.
  • the second solution firstly requires the separation of the actinides with a high degree of purity before irradiation so as not to increase the anti-reactivity. Furthermore, it is not certain that the yield from the cracked actinide / actinide formed operation is positive or sufficient, and this technique, which appears difficult to implement, cannot lead to total destruction of the actinides. In addition, it has the disadvantage of being of high cost and requiring the use of a nuclear reactor.
  • the present invention specifically relates to a device for conditioning radioactive waste consisting essentially of actinides with a long and / or medium period, which overcomes the drawbacks mentioned above, while offering sufficient guarantees of safety and security.
  • the quantities of actinide elements with long and / or medium period, of actinide emitting elements a with short period (at most 100 years) and of light elements being chosen in such a way that a sufficient quantity of neutrons is produced for obtain the destruction of actinide elements with a long and / or medium period by autofission and / or capture and / or decay, and their conversion into non-radioactive or radioactive elements of short period or into actinide elements which can be used industrially.
  • the reaction (a, n) between the emitter a with a period at most equal to 100 years and a light element such as boron-11, fluorine, beryllium, carbon, etc. is used to produce fast neutrons with an energy higher than 4 MeV and these fast neutrons formed "in situ" in the packaging are used to split or transmute actinides with long or medium period and to initiate the autofission chain.
  • the packaging can be reprocessed in order to recover the interesting actinide elements.
  • actinides with a medium period are understood to mean actinides with a period of 100 to 1,000 years and by actinides with a long period, actinides with a period greater than 1,000 years.
  • Examples of long-lived actinides include 23 'Np, 243 Am, 245 Cm, 242 PU.
  • the overall yield of the autofission ultimately depends on the fission yield, but this operation is limited by the quantity of neutrons produced which is itself conditioned by the number of particles emitted.
  • the number of particles a produced in a period Ta per gram of actinide is approximately 1.2-10 21 particles a.
  • R is the reaction yield (a, n) the number of neutrons produced per gram of actinide in a period T "is about 1.2.10 21 R neutrons. Also, to maximize the production of neutrons, there must be a period T ⁇ as short as possible, but remaining compatible with the waste produced (cooling time and quantity produced) and there must be a maximum yield R which is linked to the nature of the light element used.
  • the mixture of actinides and of the light element (s) is placed in a sealed envelope, reflecting or absorbing neutrons, preferably spherical with a diameter of less than 10 cm, so defining a central region constituted by a mixture of the actinide emitting element or elements a having a period at most equal to 100 years and of the light element or elements capable of generating neutrons by reaction (a, n), and a peripheral region surrounding the central region constituted by a mixture of the emitting actinide element or elements with a medium and / or long period and the light element or elements capable of generating neutrons by reaction ( ⁇ , n).
  • the mixture placed inside a sealed envelope, reflecting or absorbing neutrons comprises three regions, a first central region constituted by a mixture of the emitting actinide element or elements a having a period at most equal to 100 years with the light element or elements capable of generating neutrons by reaction (a, n), a second region surrounding the central region constituted by a mixture of at least one actinide emitting element a of medium period with at least one light element capable of generating neutrons by reaction (a, n ), and a third region surrounding the second region constituted by a mixture of the or of the actinide emitting elements has a long period with the light element (s) capable of generating ne utrons by reaction (a, n).
  • the various constituents, actinides and light elements can be homogeneously mixed inside a sealed envelope, reflecting or absorbing neutrons, whose shape and dimensions are not limited by the effectiveness of neutron collisions on actinides, as in the previous embodiments; one could, for example, use a cylindrical container with a diameter of about one meter.
  • the mixture of actinides and light elements confined in said container can be obtained from a mixture of the various constituents in a finely divided state, for example in the form of powders having particle sizes less than 20 ⁇ m.
  • the powder mixture is generally subjected to compaction followed possibly by sintering.
  • the mixture can also be obtained directly in the form of a solid solution, by direct formation of borides or berylliides of the actinide elements, such as UB. 2 CmB ,, AmB 6 , AmBe., NpB, etc.
  • At least part of the actinide elements entering into the composition of the mixture is associated with boron or beryllium in the form of boride or berylliide.
  • actinides and light elements are combined in the form of compounds such as borides or berylliides, it is possible to obtain a very intimate mixture and to precisely control the concentration of actinides by controlling the stoichiometric ratio of compound and avoiding the presence of precipitates of light elements or actinides.
  • the characteristics of any one of the first two modes are combined with those of the third, by disposing in a container such as that used in the third embodiment, mini- spheres with concentric layers, i.e. spherical envelopes with a diameter of less than 10 cm. waterproof, reflecting or absorbing neutrons, each containing mixtures of ⁇ -emitting actinide element (s), a emitting element (s) a and light element (s) arranged in concentric layers as in any of the first two embodiments.
  • mini-spheres the diameter of which is preferably of the order of a millimeter, can be obtained, for example, by the sol-gel process as described by HD RINGEL and E.
  • the actinide elements with a long period can be chosen from 237Np, 243 Am, 2 4 5 Cm , 2 4 2Pu.
  • the actinide emitting elements a having an average period can be chosen from 24 Am and 242m Am.
  • the actinide emitting elements a having a period at most equal to 100 years are advantageously chosen from 242 Cm, 244 Cm, 238 Pu, 241 pu and z32 U.
  • the light elements used are advantageously chosen from '° B, 11 B, 9 Be, C, O and F.
  • the light element which has a high reaction yield (a, n) is chosen, for example beryllium whose yield is approximately 70 neutrons for 10 6 particles a or boron whose yield is around 20 neutrons for 10 6 ⁇ particles, with a particles of 5.3 MeV.
  • each fast neutron produced reacts with an actinide atom to cause its fission, which, on the other hand, leads to the production of more than two fast neutrons on average.
  • a large number of long-term actinide fissions can be obtained by promoting neutron collisions with actinides by a chosen distribution of the different atoms in the mixture as seen above and by choosing so appropriate the relative concentrations of the different actinide elements and the light elements as a function of the mean fission cross section of the actinides and of the balance of transmutation and fission reactions, and of the concentration of neutrons formed.
  • the overall performance of the autofission can be further increased by placing a layer of neutron reflective material between the outer shell and the mixture of the actinide elements with the light element (s).
  • the neutron reflective material can be boron, water, graphite, steel, etc.
  • the actinide elements present in the packaging device of the invention are preferably used in a relatively pure form to obtain the best fission yield.
  • the actinide elements are isolated during the reprocessing of the irradiated fuels by extraction techniques by acid solvent and they are recovered in the organic solution or the aqueous extraction solution by precipitation techniques, which makes it possible to separate them from the other elements with a good degree of purity.
  • a mixture of several actinides is generally obtained and this mixture can be used directly in the packaging device of the invention.
  • the device comprises a spherical outer envelope 1 made for example of steel, inside which is placed the mixture of actinide elements and light elements.
  • the second embodiment of the device of the invention was used, namely an arrangement of the mixture in the form of three concentric regions of different compositions.
  • the first region 3 which constitutes the source of neutrons and comprises a mixture of emitting elements a with short period with a light element capable of producing neutrons by reaction ( ⁇ , n).
  • This region 3 is constituted, for example, by a gram of a source of 242 cm and / or 244 cm with beryllium or boron.
  • the second region 5 which is constituted by a layer of an actinide element with a medium period such as 242 Am which has a high neutron capture section and also plays the role of emitter.
  • this layer also contains boron-11 or beryllium.
  • the thickness of the second region 5 can be about 1 cm or more.
  • the third region 7 which constitutes the target is formed of a mixture of long-lived actinides such as 237 Np with 9 Be or "B.
  • the thickness of this third region is substantially equal to the thickness of the second region 5.
  • This third region 7 is surrounded by a layer 9 of neutron reflective material constituted by boron-10, thanks to the use of beryllium in the first central region 3. fast neutrons are produced with a relatively high yield.
  • 242 Cm we produce about 2.10 ° neutrons / gram per second and if we use z44 Cm, we produce about 4 108 neutrons per gram per second.
  • neutrons are used to split the americium 241 present in zone 5 which in turn emits other neutrons capable of splitting and / or transforming by reaction of transmutation, fission and / or capture the neptunium 237 present in the region 7 in 232 U.
  • the weight concentrations of actinides and of light elements are of the order of 95% and 5% respectively.

Abstract

The conditioning device comprises an outer sealed envelope (1) inside which there is arranged a mixture formed of at least one emitter actinide element alpha with a medium and/or long period such as 237Np, at least one emitter element alpha having a period shorter than 100 years such as 242Cm or 244Cm and at least one light element such as beryllium or boron capable of generating neutrons by reaction (alpha, n). The presence of those different elements enables to obtain a destruction in situ of the long or medium period actinide elements by self-fission under the influence of the neutrons produced by reaction of the particles alpha with the light element.

Description

La présente invention a pour objet un dispositif de conditionnement de déchets radioactifs constitués essentiellement par des actinides à période moyenne et/ou longue.The present invention relates to a device for conditioning radioactive waste consisting essentially of actinides with a medium and / or long period.

Dans les réacteurs nucléaires actuellement en cours d'exploitation, il se forme de grandes quantités d'actinides comme on peut le voir sur le tableau annexé qui donne les quantités des différents isotopes des actinides formés par tonne de combustible neuf irradié dans deux types de réacteurs développés industriellement dans le monde, qui sont les réacteurs à eau légère et les réacteurs à neutrons rapides.In nuclear reactors currently in operation, large quantities of actinides are formed, as can be seen in the attached table which gives the quantities of the different isotopes of actinides formed per tonne of new fuel irradiated in two types of reactors. industrially developed in the world, which are light water reactors and fast neutron reactors.

Certains des actinides produits ne constituent pas réellement des déchets car ils peuvent être utilisés comme combustibles nucléaires dans d'autres réacteurs. C'est le cas en particulier de certains isotopes du plutonium et de l'uranium.Some of the actinides produced do not actually constitute waste since they can be used as nuclear fuel in other reactors. This is particularly the case for certain isotopes of plutonium and uranium.

En revanche, d'autres éléments actinides tels que 237Np, 241Am, 243Am, 244Cm qui sont produits à des teneurs non négligeables, ne sont pas réutilisables comme combustible et constituent de ce fait des déchets au même titre que les produits de fission ou les produits d'activation des gaines et des structures de réacteurs. De plus, ces déchets présentent l'inconvénient d'avoir pour la plupart des périodes extrêmement longues, ce qui pose un problème de conditionnement et de stockage à long terme dans des conditions de sécurité et de sûreté satisfaisantes.On the other hand, other actinide elements such as 237 Np, 241 Am, 243 Am, 244 Cm which are produced at significant contents, are not reusable as fuel and therefore constitute waste in the same way as the products of fission or activation products of the sheaths and reactor structures. In addition, this waste has the disadvantage of having, for the most part, extremely long periods, which poses a problem of conditioning and long-term storage under satisfactory safety and security conditions.

Jusqu'à présent, deux solutions ont été envisagées pour le conditionnement de ces déchets, la première solution consiste à stocker ces déchets en couches géologiques stables, après les avoir introduits dans des matrices en verre ou en résine. La deuxième solution consiste à transformer ces déchets dans un réacteur nucléaire, par réaction de fission ou de transmutation en éléments à période beaucoup plus courte ou en isotopes fissibles utilisables dans des réacteurs nucléaires.Up to now, two solutions have been envisaged for the conditioning of this waste, the first solution consists in storing this waste in stable geological layers, after having introduced them into glass or resin matrices. The second solution consists in transforming this waste in a nuclear reactor, by reaction of fission or transmutation into elements with much shorter period or into fissile isotopes usable in nuclear reactors.

La première solution nécessite une infrastructure complexe de conditionnement dans les matrices en verre ou en résine. Pour des teneurs élevées en actinides, la stabilité de ces matrices n'est pas garantie à très long terme.The first solution requires a complex packaging infrastructure in glass or resin matrices. For high levels of actinides, the stability of these matrices is not guaranteed in the very long term.

La seconde solution nécessite tout d'abord la séparation des actinides avec un degré de pureté élevé avant irradiation pour ne pas augmenter l'anti-réactivité. Par ailleurs, il n'est pas certain que le rendement de l'opération actinides fissionnés/actinides formés soit positif ou soit suffisant, et cette technique qui paraît difficile à mettre en oeuvre ne peut conduire à une destruction totale des actinides. De plus, elle présente l'inconvénient d'être d'un coût élevé et de nécessiter l'utilisation d'un réacteur nucléaire.The second solution firstly requires the separation of the actinides with a high degree of purity before irradiation so as not to increase the anti-reactivity. Furthermore, it is not certain that the yield from the cracked actinide / actinide formed operation is positive or sufficient, and this technique, which appears difficult to implement, cannot lead to total destruction of the actinides. In addition, it has the disadvantage of being of high cost and requiring the use of a nuclear reactor.

La présente invention a précisément pour objet un dispositif de conditionnement de déchets radioactifs constitués essentiellement par des actinides à période longue et/ou moyenne, qui pallie les inconvénients rappelés ci-dessus, tout en offrant les garanties suffisantes de sûreté et de sécurité.The present invention specifically relates to a device for conditioning radioactive waste consisting essentially of actinides with a long and / or medium period, which overcomes the drawbacks mentioned above, while offering sufficient guarantees of safety and security.

Le dispositif selon l'invention de conditionnement de déchets radioactifs constitués essentiellement par des actinides, se caractérise en ce qu'il comprend, une enveloppe externe étanche à l'intérieur de laquelle est disposé un mélange comprenant :

  • - au moins un élément actinide émetteur a à période longue ou moyenne,
  • - au moins un élément actinide émetteur a ayant une période courte au plus égale à 100 ans, et
  • - au moins un élément léger, capable d'engendrer des neutrons par réaction (a, n).
The device according to the invention for packaging radioactive waste consisting essentially of actinides, is characterized in that it comprises, a sealed external envelope inside which a mixture comprising:
  • - at least one emitting actinide element a with a long or medium period,
  • - at least one emitting actinide element a having a short period at most equal to 100 years, and
  • - at least one light element, capable of generating neutrons by reaction (a, n).

Les quantités d'éléments actinides à longue et/ou moyenne période, d'éléments actinides émetteurs a à période courte (au plus 100 ans) et d'éléments légers étant choisies de façon telle que l'on produise une quantité de neutrons suffisante pour obtenir la destruction des éléments actinides à période longue et/ou moyenne par autofission et/ou capture et/ou décroissance, et leur conversion en éléments non radioactifs ou radioactifs de période courte ou en éléments actinides utilisables industriellement.The quantities of actinide elements with long and / or medium period, of actinide emitting elements a with short period (at most 100 years) and of light elements being chosen in such a way that a sufficient quantity of neutrons is produced for obtain the destruction of actinide elements with a long and / or medium period by autofission and / or capture and / or decay, and their conversion into non-radioactive or radioactive elements of short period or into actinide elements which can be used industrially.

Grâce à la présence de ces différents éléments dans le mélange disposé à l'intérieur de l'enveloppe, on peut obtenir une destruction « in situ des éléments actinides à périodes longue et/ou moyenne par autofission, sans avoir recours à l'emploi d'un réacteur nucléaire générateur de nouveaux déchets.Thanks to the presence of these various elements in the mixture placed inside the envelope, it is possible to obtain an "in situ destruction of actinide elements with long and / or medium periods by autofission, without resorting to the use of 'a nuclear reactor generating new waste.

En effet, on utilise la réaction (a, n) entre l'émetteur a à période au plus égale à 100 ans et un élément légertel que le bore-11, le fluor, le béryllium, le carbone, etc., pour produire des neutrons rapides ayant une énergie supérieure à 4 MeV et ces neutrons rapides formés « in situ » dans le conditionnement sont utilisés pour fissionner ou transmuter les actinides à période longue ou moyenne et amorcer la chaîne d'autofission.In fact, the reaction (a, n) between the emitter a with a period at most equal to 100 years and a light element such as boron-11, fluorine, beryllium, carbon, etc., is used to produce fast neutrons with an energy higher than 4 MeV and these fast neutrons formed "in situ" in the packaging are used to split or transmute actinides with long or medium period and to initiate the autofission chain.

A la suite de ces réactions, tous les actinides à période longue se transforment en un temps relativement court par décroissance a et/ou par capture et/ou par fission en éléments non radioactifs, en éléments radioactifs de période courte ou en actinides pouvant être utilisés comme combustibles pour réacteurs nucléaires ou présentant de l'intérêt pour d'autres applications.As a result of these reactions, all long-lived actinides are transformed in a relatively short time by decay a and / or by capture and / or fission into non-radioactive elements, into short-lived radioactive elements or into actinides which can be used. as fuel for nuclear reactors or of interest for other applications.

Dans ce dernier cas, on peut réaliser un retraitement du conditionnement en vue de récupérer les éléments actinides intéressants.In the latter case, the packaging can be reprocessed in order to recover the interesting actinide elements.

On précise que. dans l'invention, on entend par actinides à période moyenne, les actinides dont la période est de 100 à 1 000 ans et par actinides à période longue, les actinides dont la période est supérieure à 1 000 ans.It is specified that. in the invention, actinides with a medium period are understood to mean actinides with a period of 100 to 1,000 years and by actinides with a long period, actinides with a period greater than 1,000 years.

A titre d'exemple d'actinides à période longue, on peut citer 23'Np, 243Am, 245Cm, 242PU.Examples of long-lived actinides include 23 'Np, 243 Am, 245 Cm, 242 PU.

A titre d'exemple d'actinides à période moyenne, on peut citer 24Am et 242mAm.By way of example of actinides with a medium period, there may be mentioned 24 Am and 242m Am.

Parmi ces actinides à période moyenne ou longue, 237Np, 241Am. 242mAm et 243Am sont intéressants car ils conduisent par capture neutronique à des actinides émetteurs a de plus courte période. Lors de ces réactions, on peut former de nouveaux actinides à courte période, qui sont des émetteurs a ; ceci permet d'engendrer dans le dispositif de conditionnement des neutrons supplémentaires par réaction (α, n) avec les éléments légers présents dans le mélange.Among these actinides with a medium or long period, 237 Np, 241 Am. 242m Am and 243 Am are interesting because they lead by neutron capture to actinide emitters of shorter period. During these reactions, new short-lived actinides can be formed which are a-emitters; this makes it possible to generate additional neutrons in the conditioning device by reaction (α, n) with the light elements present in the mixture.

En effet, le rendement global de l'autofission dépend en dernier lieu du rendement de fission mais cette opération est limitée par la quantité de neutrons produite qui est elle-même conditionnée par le nombre de particules a émises. Le nombre de particules a produites en une période Ta par gramme d'actinide est environ 1.2-1021particules a.In fact, the overall yield of the autofission ultimately depends on the fission yield, but this operation is limited by the quantity of neutrons produced which is itself conditioned by the number of particles emitted. The number of particles a produced in a period Ta per gram of actinide is approximately 1.2-10 21 particles a.

De ce fait, si R est le rendement de la réaction (a, n) le nombre de neutrons produits par gramme d'actinide en une période T" est d'environ 1,2.1021 R neutrons. Aussi, pour maximiser la production de neutrons, il faut une période Tα la plus courte possible, mais restant compatible avec les déchets produits (temps de refroidissement et quantité produite) et il faut un rendement R maximum qui est lié à la nature de l'élément léger utilisé.Therefore, if R is the reaction yield (a, n) the number of neutrons produced per gram of actinide in a period T "is about 1.2.10 21 R neutrons. Also, to maximize the production of neutrons, there must be a period T α as short as possible, but remaining compatible with the waste produced (cooling time and quantity produced) and there must be a maximum yield R which is linked to the nature of the light element used.

Par ailleurs, on peut faciliter la production des neutrons à l'intérieur du dispositif de conditionnement et les collisions des neutrons produits avec les actinides à période longue, en choisissant une répartition appropriée des atomes des éléments émetteurs a à période courte, des éléments actinides à période longue et des éléments légers à l'intérieur du dispositif, c'est-à-dire en séparant les émetteurs a « source à à période courte des actinides « cible à à période longue. Toutefois, la distance entre les « sources» de neutrons et les actinides « cible ne doit pas dépasser la dizaine de centimètres pour que les collisions des neutrons sur les actinides restent efficaces.Furthermore, it is possible to facilitate the production of neutrons inside the conditioning device and the collisions of the neutrons produced with actinides with a long period, by choosing an appropriate distribution of the atoms of the emitting elements a with short period, of the actinide elements with long period and light elements inside the device, that is to say by separating the emitters a "source with short period from actinides" target with long period. However, the distance between the “sources” of neutrons and the target “actinides” must not exceed ten centimeters so that the collisions of the neutrons on the actinides remain effective.

Ainsi, selon un premier mode de réalisation du dispositif de l'invention, le mélange des actinides et du ou des éléments légers est disposé dans une enveloppe étanche, réfléchissant ou absorbant les neutrons, de préférence sphérique de diamètre inférieur à 10 cm, de façon à définir une région centrale constituée par un mélange du ou des éléments actinides émetteurs a ayant une période au plus égale à 100 ans et du ou des éléments légers capables d'engendrer des neutrons par réaction (a, n), et une région périphérique entourant la région centrale constituée par un mélange du ou des éléments actinides émetteurs a à période moyenne et/ou longue et du ou des éléments légers capables d'engendrer des neutrons par réaction (α, n).Thus, according to a first embodiment of the device of the invention, the mixture of actinides and of the light element (s) is placed in a sealed envelope, reflecting or absorbing neutrons, preferably spherical with a diameter of less than 10 cm, so defining a central region constituted by a mixture of the actinide emitting element or elements a having a period at most equal to 100 years and of the light element or elements capable of generating neutrons by reaction (a, n), and a peripheral region surrounding the central region constituted by a mixture of the emitting actinide element or elements with a medium and / or long period and the light element or elements capable of generating neutrons by reaction (α, n).

Selon un second mode de réalisation du dispositif de l'invention, dans lequel on retrouve également cette disposition avantageuse des actinides « source et des actinides « cible », le mélange disposé à l'intérieur d'une enveloppe étanche, réfléchissant ou absorbant les neutrons, de préférence sphérique de diamètre inférieur à 10 cm, comprend trois régions, une première région centrale constituée par un mélange du ou des éléments actinides émetteurs a ayant une période au plus égale à 100 ans avec le ou les éléments légers capables d'engendrer des neutrons par réaction (a, n), une deuxième région entourant la région centrale constituée par un mélange d'au moins un élément actinide émetteur a de période moyenne avec au moins un élément léger capable d'engendrer des neutrons par réaction (a, n), et une troisième région entourant la deuxième région constituée par un mélange du au des éléments actinides émetteurs a de période longue avec le ou les éléments légers capables d'engendrer des neutrons par réaction (a, n).According to a second embodiment of the device of the invention, in which we also find this advantageous arrangement of "source" actinides and "target" actinides, the mixture placed inside a sealed envelope, reflecting or absorbing neutrons , preferably spherical with a diameter of less than 10 cm, comprises three regions, a first central region constituted by a mixture of the emitting actinide element or elements a having a period at most equal to 100 years with the light element or elements capable of generating neutrons by reaction (a, n), a second region surrounding the central region constituted by a mixture of at least one actinide emitting element a of medium period with at least one light element capable of generating neutrons by reaction (a, n ), and a third region surrounding the second region constituted by a mixture of the or of the actinide emitting elements has a long period with the light element (s) capable of generating ne utrons by reaction (a, n).

Selon un troisième mode de réalisation du dispositif de l'invention, les différents constituants, actinides et éléments légers, peuvent être mélangés de façon homogène à l'intérieur d'une enveloppe étanche, réfléchissant ou absorbant les neutrons, dont la forme et les dimensions ne sont pas limitées par l'efficacité des collisions des neutrons sur les actinides, comme dans les modes de réalisation précédents ; on pourra, par exemple, utiliser un conteneur cylindrique de un mètre de diamètre environ.According to a third embodiment of the device of the invention, the various constituents, actinides and light elements, can be homogeneously mixed inside a sealed envelope, reflecting or absorbing neutrons, whose shape and dimensions are not limited by the effectiveness of neutron collisions on actinides, as in the previous embodiments; one could, for example, use a cylindrical container with a diameter of about one meter.

Le mélange d'actinides et d'éléments légers confiné dans ledit conteneur peut être obtenu à partir d'un mélange des différents constituants à l'état finement divisé, par exemple sous la forme de poudres ayant des granulométries inférieures à 20 µm. Dans ce cas, on soumet généralement le mélange de poudres à un compactage suivi éventuellement d'un frittage.The mixture of actinides and light elements confined in said container can be obtained from a mixture of the various constituents in a finely divided state, for example in the form of powders having particle sizes less than 20 μm. In this case, the powder mixture is generally subjected to compaction followed possibly by sintering.

On peut aussi obtenir directement le mélange sous la forme d'une solution solide, par formation directe de borures ou de bérylliures des éléments actinides, tels que UB.2 CmB,, AmB6, AmBe., NpB, etc.The mixture can also be obtained directly in the form of a solid solution, by direct formation of borides or berylliides of the actinide elements, such as UB. 2 CmB ,, AmB 6 , AmBe., NpB, etc.

Dans ce cas, au moins une partie des éléments actinides entrant dans la composition du mélange est associée au bore ou au béryllium sous la forme de borure ou de bérylliure.In this case, at least part of the actinide elements entering into the composition of the mixture is associated with boron or beryllium in the form of boride or berylliide.

Dans le cas, où l'on associe les actinides et les éléments légers sous la forme de composés tels que des borures ou des bérylliures, on peut obtenir un mélange très intime et contrôler avec précision la concentration d'actinides en maîtrisant le rapport stoechiométrique du composé et en évitant la présence de précipités d'éléments légers ou d'actinides.In the case where actinides and light elements are combined in the form of compounds such as borides or berylliides, it is possible to obtain a very intimate mixture and to precisely control the concentration of actinides by controlling the stoichiometric ratio of compound and avoiding the presence of precipitates of light elements or actinides.

Selon un quatrième mode de réalisation du dispositif de l'invention, on combine les caractéristiques de l'un quelconque des deux premiers modes avec celles du troisième, en disposant dans un conteneur tel que celui utilisé dans le troisième mode de réalisation, des mini-sphères à couches concentriques, soit des enveloppes sphériques de diamètre inférieur à 10 cm. étanches, réfléchissant ou absorbant les neutrons, contenant chacune des mélanges d'élément(s) actinide(s) émetteur(s) α, d'élément(s) émetteur(s) a et d'élément(s) léger(s) disposés en couches concentriques comme dans l'un quelconque des deux premiers modes de réalisation. Ces mini-sphères, dont le diamètre est de préférence de l'ordre du millimètre, peuvent être obtenues, par exemple, par le procédé sol-gel tel que décrit par H. D. RINGEL et E. ZIMMER dans Nuclear Technology, vol. 45, n° 3, p. 287-298 (oct. 1979) et par B.L. ALLEN, L. H. FORD et J. V. SHENNAN dans Nuclear Technology sept. 1977, vol. 35, p. 246-251.According to a fourth embodiment of the device of the invention, the characteristics of any one of the first two modes are combined with those of the third, by disposing in a container such as that used in the third embodiment, mini- spheres with concentric layers, i.e. spherical envelopes with a diameter of less than 10 cm. waterproof, reflecting or absorbing neutrons, each containing mixtures of α-emitting actinide element (s), a emitting element (s) a and light element (s) arranged in concentric layers as in any of the first two embodiments. These mini-spheres, the diameter of which is preferably of the order of a millimeter, can be obtained, for example, by the sol-gel process as described by HD RINGEL and E. ZIMMER in Nuclear Technology, vol. 45, n ° 3, p. 287-298 (Oct. 1979) and by BL ALLEN, LH FORD and JV SHENNAN in Nuclear Technology Sept. 1977, vol. 35, p. 246-251.

Ces configurations permettent en particulier de mieux utiliser les neutrons produits par réaction (a, n) ou par réaction (n. 2n) ou (n, 3n).These configurations allow in particular better use of the neutrons produced by reaction (a, n) or by reaction (n. 2n) or (n, 3n).

Dans tous ces modes de réalisation du dispositif de l'invention, les éléments actinides à période longue peuvent être choisis parmi 237Np, 243Am, 245Cm, 242Pu.In all these embodiments of the device of the invention, the actinide elements with a long period can be chosen from 237Np, 243 Am, 2 4 5 Cm , 2 4 2Pu.

Les éléments actinides émetteurs a ayant une période moyenne peuvent être choisis parmi 24Am et 242mAm. Les éléments actinides émetteurs a ayant une période au plus égale à 100 ans sont avantageusement choisis parmi 242Cm, 244Cm, 238Pu, 241pu et z32U. Les éléments légers utilisés sont avantageusement choisis parmi '°B, 11B, 9Be, C, O et F.The actinide emitting elements a having an average period can be chosen from 24 Am and 242m Am. The actinide emitting elements a having a period at most equal to 100 years are advantageously chosen from 242 Cm, 244 Cm, 238 Pu, 241 pu and z32 U. The light elements used are advantageously chosen from '° B, 11 B, 9 Be, C, O and F.

De préférence, on choisit l'élément léger qui présente un rendement de la réaction (a, n) élevé, par exemple le béryllium dont le rendement est d'environ 70 neutrons pour 106 particules a ou le bore dont le rendement est d'environ 20 neutrons pour 106 particules α, avec des particules a de 5,3 MeV.Preferably, the light element which has a high reaction yield (a, n) is chosen, for example beryllium whose yield is approximately 70 neutrons for 10 6 particles a or boron whose yield is around 20 neutrons for 10 6 α particles, with a particles of 5.3 MeV.

Ainsi, avec de tels éléments, on peut obtenir une production de neutrons rapides suffisante pour obtenir la fission des éléments actinides à périodes longue et/ou moyenne. De préférence, pour favoriser cette production, on mélange intimement les éléments légers avec les éléments actinides « source =.Thus, with such elements, it is possible to obtain a production of fast neutrons sufficient to obtain the fission of actinide elements with long and / or medium periods. Preferably, to promote this production, the light elements are intimately mixed with the "source =" actinide elements.

Cependant, on ne peut envisager que chaque neutron rapide produit réagisse avec un atome d'actinide pour provoquer sa fission, ce qui, d'autre part, entraîne la production de plus de deux neutrons rapides en moyenne. Cependant, on peut obtenir un nombre important de fissions de l'actinide à période longue en favorisant les collisions des neutrons avec les actinides par une répartition choisie des différents atomes dans le mélange comme on l'a vu ci-dessus et en choisissant de façon appropriée les concentrations relatives des différents éléments actinides et des éléments légers en fonction de la section efficace de fission moyenne des actinides et du bilan des réactions de transmutation et de fission, et de la concentration de neutrons formés.However, it cannot be envisaged that each fast neutron produced reacts with an actinide atom to cause its fission, which, on the other hand, leads to the production of more than two fast neutrons on average. However, a large number of long-term actinide fissions can be obtained by promoting neutron collisions with actinides by a chosen distribution of the different atoms in the mixture as seen above and by choosing so appropriate the relative concentrations of the different actinide elements and the light elements as a function of the mean fission cross section of the actinides and of the balance of transmutation and fission reactions, and of the concentration of neutrons formed.

De plus, on peut aussi utiliser les éléments légers pour émettre des particules a par réaction (n, a) des neutrons avec les éléments légers tels que le bore-10 utilisé, dans ce cas, en couverture.In addition, one can also use the light elements to emit particles a by reaction (n, a) neutrons with the light elements such as boron-10 used, in this case, in cover.

On peut encore augmenter le rendement global de l'autofission en disposant une couche de matériau réflecteur de neutrons entre l'enveloppe externe et le mélange des éléments actinides avec le ou les éléments légers.The overall performance of the autofission can be further increased by placing a layer of neutron reflective material between the outer shell and the mixture of the actinide elements with the light element (s).

Le matériau réflecteur de neutrons peut être du bore, de l'eau, du graphite, de l'acier, etc.The neutron reflective material can be boron, water, graphite, steel, etc.

On peut aussi améliorer le rendement de fission par thermalisation des neutrons produits par réaction (a, n) en introduisant dans le mélange ou dans la zone du mélange qui comprend les actinides « cible« un matériau ralentisseur de neutrons tel que le graphite, l'eau, etc.It is also possible to improve the fission yield by thermalization of the neutrons produced by reaction (a, n) by introducing into the mixture or in the zone of the mixture which comprises the "target" actinides a neutron retarding material such as graphite, water, etc.

Enfin, en dosant de façon précise les actinides et les éléments légers, on peut obtenir une augmentation sensible de la production de neutrons par effets Doppler.Finally, by precisely measuring actinides and light elements, we can obtain a significant increase in the production of neutrons by Doppler effects.

Les éléments actinides présents dans le dispositif de conditionnement de l'invention, sont utilisés de préférence sous une forme relativement pure pour obtenir le meilleur rendement de fission.The actinide elements present in the packaging device of the invention are preferably used in a relatively pure form to obtain the best fission yield.

Toutefois, si ces éléments ne présentent pas un degré de pureté suffisant, on peut jouer sur les concentrations en actinides et en éléments légers afin de tenir compte des impuretés absorbant ou thermalisant les neutrons, et obtenir ainsi un bon rendement de fission.However, if these elements do not have a sufficient degree of purity, it is possible to act on the concentrations of actinides and of light elements in order to take account of the impurities absorbing or thermalizing the neutrons, and thus obtaining a good fission yield.

Généralement, on isole les éléments actinides lors du retraitement des combustibles irradiés par des techniques d'extraction par solvant acide et on les récupère dans la solution organique ou la solution aqueuse d'extraction par des techniques de précipitation, ce qui permet de les séparer des autres éléments avec un bon degré de pureté. On obtient généralement un mélange de plusieurs actinides et ce mélange peut être utilisé directement dans le dispositif de conditionnement de l'invention.Generally, the actinide elements are isolated during the reprocessing of the irradiated fuels by extraction techniques by acid solvent and they are recovered in the organic solution or the aqueous extraction solution by precipitation techniques, which makes it possible to separate them from the other elements with a good degree of purity. A mixture of several actinides is generally obtained and this mixture can be used directly in the packaging device of the invention.

D'autres caractéristiques et avantages de l'invention apparaîtront mieux à la lecture de la description qui suit donnée bien entendu à titre d'exemple illustratif et non limitatif en référence au dessin annexé qui représente en coupe un dispositif de conditionnement selon l'invention.Other characteristics and advantages of the invention will appear better on reading the description which follows given of course by way of illustrative and nonlimiting example with reference to the appended drawing which shows in section a packaging device according to the invention.

Sur cette figure, on voit que le dispositif comprend une enveloppe externe 1 sphérique réalisée par exemple en acier, à l'intérieur de laquelle est disposé le mélange des éléments actinides et des éléments légers.In this figure, it can be seen that the device comprises a spherical outer envelope 1 made for example of steel, inside which is placed the mixture of actinide elements and light elements.

Dans le dispositif représenté sur le dessin, on a utilisé le second mode de réalisation du dispositif de l'invention, soit une disposition du mélange sous la forme de trois régions concentriques de compositions différentes. Ainsi, on trouve au centre la première région 3 qui constitue la source de neutrons et comprend un mélange d'éléments émetteurs a à période courte avec un élément léger capable de produire des neutrons par réaction (α, n). Cette région 3 est constituée, par exemple, par un gramme d'une source de 242Cm et/ou 244Cm avec du béryllium ou du bore. Autour de cette région qui constitue la source, on trouve la seconde région 5 qui est constituée par une couche d'un élément actinide à période moyenne tel que 242Am qui présente une section de capture des neutrons élevée et joue également le rôle d'émetteur α, cette couche contient également du bore-11 ou du béryllium.In the device shown in the drawing, the second embodiment of the device of the invention was used, namely an arrangement of the mixture in the form of three concentric regions of different compositions. Thus, there is in the center the first region 3 which constitutes the source of neutrons and comprises a mixture of emitting elements a with short period with a light element capable of producing neutrons by reaction (α, n). This region 3 is constituted, for example, by a gram of a source of 242 cm and / or 244 cm with beryllium or boron. Around this region which constitutes the source, there is the second region 5 which is constituted by a layer of an actinide element with a medium period such as 242 Am which has a high neutron capture section and also plays the role of emitter. α, this layer also contains boron-11 or beryllium.

L'épaisseur de la seconde région 5 peut être d'environ 1 cm ou plus. Autour de cette région 5. la troisième région 7 qui constitue la cible, est formée d'un mélange d'actinides à période longue tels que 237Np avec du 9Be ou du "B. L'épaisseur de cette troisième région est sensiblement égale à l'épaisseur de la seconde région 5. Cette troisième région 7 est entourée par une couche 9 de matériau réflecteur de neutrons constituée par du bore-10. Grâce à l'utilisation de béryllium dans la première région centrale 3. on produit des neutrons rapides avec un rendement relativement élevé. Ainsi, si l'on utilise 242Cm, on produit environ 2.10'° neutrons/gramme et par seconde et si l'on utilise z44Cm, on produit environ 4 108 neutrons par gramme et par seconde.The thickness of the second region 5 can be about 1 cm or more. Around this region 5. the third region 7 which constitutes the target, is formed of a mixture of long-lived actinides such as 237 Np with 9 Be or "B. The thickness of this third region is substantially equal to the thickness of the second region 5. This third region 7 is surrounded by a layer 9 of neutron reflective material constituted by boron-10, thanks to the use of beryllium in the first central region 3. fast neutrons are produced with a relatively high yield. Thus, if we use 242 Cm, we produce about 2.10 ° neutrons / gram per second and if we use z44 Cm, we produce about 4 108 neutrons per gram per second.

Ces neutrons sont utilisés pourfissionner l'américium 241 présent dans la zone 5 qui à son tour émet d'autres neutrons capables de fissionner et/ou de transformer par réaction de transmutation, de fission et/ou de capture le neptunium 237 présent dans la région 7 en 232U.These neutrons are used to split the americium 241 present in zone 5 which in turn emits other neutrons capable of splitting and / or transforming by reaction of transmutation, fission and / or capture the neptunium 237 present in the region 7 in 232 U.

Dans tous les modes de réalisation, les concentrations pondérales des actinides et des éléments légers sont respectivement de l'ordre de 95 % et de 5 %.

Figure imgb0001
In all the embodiments, the weight concentrations of actinides and of light elements are of the order of 95% and 5% respectively.
Figure imgb0001

Claims (19)

1. Apparatus for conditioning radioactive waste essentially constituted by actinides, characterized in that it comprises a tight outer envelope (1) within which is placed a mixture incorporating at least one a emitter actinide element with a medium or long half-life, at least one a emitter actinide element having a short half-life at the most equal to 100 years and at least one light element able to produce neutrons by (a, n) reaction, the quantities of medium and/or long half-life actinide elements, short half-life a emitter actinide elements (at the most 100 years) and light elements being chosen so that an adequate neutron quantity is produced to obtain the destruction of the medium and/or long actinide elements by autofission and/or capture and/or decay and their conversion into non-radioactive elements or radioactive elements with a short half-life or industrially usable actinide elements.
2. Apparatus according to claim 1, characterized in that the mixture of the actinides and the light element or elements is placed in a tight envelope, which reflects or absorbs neutrons and which is preferably spherical having a diameter below 10 cm, so as to define a central region (3) constituted by a mixture of the a actinide emitter or emitters having a half-life at the most equal to 100 years and the light element or elements able to produce neutrons by (a, n) reaction, and a peripheral region (7) surrounding the central region constituted by a mixture of the a emitter actinide element or elements with a medium and/or long half-life and the light element or elements able to produce neutrons by (α, n) reaction.
3. Apparatus according to claim 1, characterized in that the mixture placed in a tight envelope, which reflects or absorbs neutrons and which is preferably spherical with a diameter below 10 cm, comprises three regions, namely a first central region (3) constituted by a mixture of the a emitter actinide element or elements having a half-life at the most equal to 100 years and the light element or elements able to produce neutrons by (α, n) reaction, a second region (5) surrounding the central region constituted by a mixture of a least one a emitter actinide element with a medium half-life and at least one light element able to produce neutrons by (a, n) reaction, and a third region (7) surrounding the second region constituted by a mixture of the a emitter actinide element or elements with a long half-life and the light element or elements able to produce neutrons by (a, n) reaction.
4. Apparatus according to claim 1, characterized in that the constituents of the mixture, namely α emitter actinide element or elements with a medium or long half-life, a emitter actinide elements or elements with a half-life at the most equal to 100 years and light element or elements are mixed homogeneously within a tight envelope, which reflects or absorbs neutrons.
5. Apparatus according to claim 1, characterized in that the mixture of the actinides and of the light element or elements is placed in spherical envelopes of a diameter below 10 cm, which are tight, reflect or absorb neutrons. so as to define within each spherical envelope a central region constituted by a mixture of the a emitter actinide element or elements with a half-life at the most equal to 100 years and of the light element or elements able to produce neutrons by (α, n) reaction and a peripheral region (7) surrounding the central region constituted by a mixture of the α emitter actinide element or elements with a medium and/or long half-life and the light element or elements able to produce neutrons by (a. n) reaction and wherein the spherical envelopes containing said mixtures are placed in a container forming the outer envelope of the apparatus.
6. Apparatus according to claim 1, characterized in that the mixture of the actinides and the light element or elements is placed in spherical containers with a diameter below 10 cm, which are tight and reflect or absorb neutrons, so as to define within each spherical envelope three regions, namely a first central region (3) constituted by a mixture of the a emitter actinide element or elements having a half-life at the most equal to 100 years and the light element or elements able to produce neutrons by (a. n) reaction, a second region (5) surrounding the central region constituted by a mixture of at least one a emitter actinide element having a medium half-life and at least one light element able to produce neutrons by (a, n) reaction and a third region (7) surrounding the second region constituted by a mixture of the a emitter actinide element or elements with a long half-life and the light element or elements able to produce neutrons by (a, n) reaction and wherein the spherical envelopes containing said mixtures are placed in a container constituting the outer envelope of the apparatus.
7. Apparatus according to any one of the claims 1 to 6, characterized in that a layer of neutron-reflecting material (9) is placed between the outer envelope (1) and the mixture of the actinide elements and the light element or elements.
8. Apparatus according to claim 7, characterized in that the neutron-reflecting material is boron. water. graphite, steel or any other neutron reflector.
9. Apparatus according to any one of the claims 1 to 8, characterized in that the light element or elements are chosen from among '°B, "B, 9Be, C, 0 and F.
10. Apparatus according to any one of the claims 1 to 9, characterized in that the a emitter actinide element or elements with a half-life at the most equal to 100 years is chosen from among 242Cm, 244Cm, 238pU, 241Pu and 232U.
11. Apparatus according to any of the claims 1 to 10, characterized in that the actinide elements with a long half-life are chosen from the group including 237Np, 243Am. 245Cm and 242Pu.
12. Apparatus according to either of the claims 3 and 6, characterized in that the a emitter actinide element or elements with a medium half-life are chosen from among 241Am and 242Am.
13. Apparatus according to any one of the claims 2, 3, 5 and 6, characterized in that the central region is constituted by a mixture of curium 242 and/or curium 244 with beryllium or boron.
14. Apparatus according to either of the claims 2 and 4, characterized in that the peripheral layer is constituted by a mixture of at least one actinide element chosen from among 237Np, 243Am. 5Cm and 242p U with boron.
15. Apparatus according to any one of the claims 3, 6, 10 and 13, characterized in that the second region is constituted by a mixture of at least one actinide element chosen from among 241Am and 242Cm with beryllium.
16. Apparatus according to any one of the claims 3, 6, 10, 13 and 15, characterized in that the third region is constituted by a mixture of at least one actinide element chosen from among 237Np, 243Am, 245Cm and 242PU with boron.
17. Apparatus according to any one of the claims 1 to 8, characterized in that with the light element being formed by boron, at least part of the actinide elements entering into the composition of the mixture is combined with the boron in the form of actinide boride.
18. Apparatus according to any one of the claims 1 to 8, characterized in that with the light element being beryllium, at least part of the actinide elements entering into the composition of the mixture is combined with the beryllium in the form of actinide beryllide.
19. Apparatus according to any one of the claims 1 to 18, characterized in that the weight concentrations of the actinides and light elements are respectively approximately 95 % and 5 %.
EP19850902571 1984-06-05 1985-06-04 Device for conditioning radioactive waste comprised of mediumand /or long period actinides Expired EP0186677B1 (en)

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