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VERFAHREN ZUR HERSTELLUNG EINES MATERIALS, ANGEPASST, UM AN EIN NUKLEARES BRENNSTOFFELEMENT AUF OXIDBASIS GESINTERT ZU WERDEN - Dokument EP1157391
 
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Dokumentenidentifikation EP1157391 15.01.2004
EP-Veröffentlichungsnummer 0001157391
Titel VERFAHREN ZUR HERSTELLUNG EINES MATERIALS, ANGEPASST, UM AN EIN NUKLEARES BRENNSTOFFELEMENT AUF OXIDBASIS GESINTERT ZU WERDEN
Anmelder Westinghouse Atom AB, Västerås, SE
Erfinder ABRY, Philippe, S-723 36 Västeras, SE;
BORELL, Sten, S-722 31 Västeras, SE;
ERIKSSON, Sven, S-730 50 Västeras, SE
Vertreter derzeit kein Vertreter bestellt
DE-Aktenzeichen 60006939
Vertragsstaaten DE, ES, FR
Sprache des Dokument EN
EP-Anmeldetag 08.02.2000
EP-Aktenzeichen 009098385
WO-Anmeldetag 08.02.2000
PCT-Aktenzeichen PCT/SE00/00237
WO-Veröffentlichungsnummer 0000049621
WO-Veröffentlichungsdatum 24.08.2000
EP-Offenlegungsdatum 28.11.2001
EP date of grant 03.12.2003
Veröffentlichungstag im Patentblatt 15.01.2004
IPC-Hauptklasse G21C 3/62

Beschreibung[en]
BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention related to a method for production of a nuclear fuel element with oxide base, in which the nuclear fuel with oxide base is mixed with chrome oxide and sintered into a solid body. The invention also relates to a material with oxide base adapted to be sintered to a nuclear fuel element, which comprises a nuclear fuel with oxide base and chrome oxide.

Methods and materials of the type mentioned above are already known within the field of nuclear energy applications. The nuclear fuel with oxide base may comprise UO2, ThO2, PuO2 or a mixture thereof, and is provided as powder.

Different additions of further oxides, such as TiO2, Nb2O5, Cr2O3, Al2O3, V2O5 and MgO have according to the prior art been added to the nuclear fuel with oxide base for obtaining an increase of the grain size thereof in connection with the sintering thereof, since said additions activate the crystalline growth of the grains of the nuclear fuel during the sintering.

The increased grain size results in a need of a longer time for gas enclosures in the grains to diffuse to grain boundaries and through these out of the nuclear fuel when this is used during operation. The amount of such gases, fission gases, outside the nuclear fuel element is accordingly reduced during normal operation conditions thanks to the increased grain size of the nuclear fuel.

It may also be assumed that an increased corrosion resistance results from an increased grain size of the nuclear fuel, since corrosion preferably starts at the grain boundaries and the relationship between the total grain boundary area and the volume of a nuclear fuel element is reduced, i.e. the total grain boundary area is reduced, when the grain size increases. A good corrosion resistance is desired, since the nuclear fuel may come into contact with steam or water during the operation as consequence of damage on a surrounding cladding tube. Corrosion products may then be spread further out in the plant, which should be avoided for reasons known per se.

Besides the fact that the additions mentioned above result in a larger grain size of the nuclear fuel and the advantages associated therewith, at least some of them contribute to an increase of the density of the nuclear fuel element, with respect to the weight of the very nuclear fuel, for example U, Th or Pu, in relation to the volume of the nuclear fuel element. Thus, more power may be obtained out of a given volume of the nuclear fuel.

At least some of said additions also result in an increase of the plasticity of the nuclear fuel element sintered. This results in a smaller risk of damage on surrounding cladding tubes at rapid power increases during operation, and volume changes of the nuclear fuel element associated therewith, since the fuel element with less power than otherwise acts on the cladding tube.

Cr2O3 is the addition of those mentioned above that gives the mostly noticeable result. The prior art uses therefor preferably Cr2O3 for obtaining the effects mentioned above, primarily the increase of the grain size of the nuclear fuel. However, Cr2O3 has to be considered as a poison in this context, since Cr has a comparatively large neutron absorption cross section, which in its turn may have a negative influence upon the power of the nuclear fuel element, which has been understood by the applicant. According to the prior art 1000-5000 ppm Cr is added (separate or as Cr2O3) with respect to the amount of the nuclear fuel with oxide base, for example UO2, for obtaining the effects mentioned above.

WO-A-97/06535 discloses a sintered nuclear fuel element with oxide base. The nuclear element comprises a nuclear fuel with oxide base such as uranium dioxide and plutonium dioxide. In example 4 it is proposed to add particles comprising one or more of Ti, Al, Nb, Cr and Mg. The proposed quantity of these metals is 0,01 - 1 %, i.e. 100 - 10000 ppm.

GB-A-1 334 391 discloses another sintered nuclear fuel element with oxide base. The nuclear element comprises a nuclear fuel with oxide base, such as uranium dioxide or plutonium oxide. It is proposed to add one further oxide compound, selected among aluminium, titanium, magnesium, zirconium, colombium, chromium, vanadium, iron and copper. The quantity of the added oxide compound is also 0,01 - 0,1 %, i.e. 100 - 1000 ppm.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method which benefits by the effects obtainable through addition of a further oxide, preferably chrome oxide to the nuclear fuel with oxide base at the same time as the amount of chrome oxide added is regulated while considering the negative consequences of the presence of Cr in the nuclear fuel element.

The object is achieved by the method defined in claim 1. Such amounts of added chrome oxide result in remarkably increased grain sizes of different nuclear fuels with oxide base, such as UO2 in connection with the sintering of the nuclear fuel element, at the same time as the amount Cr is kept at a lower level than before, and has accordingly a reduced negative influence upon the efficiency of the nuclear fuel element during operation, in spite of the comparatively high neutron absorption cross section thereof. A still more preferred interval with respect to the amount of Cr is 100-700 ppm.

The further metal oxide is preferably any of Nb2O5, Al2O3 and MgO. Said additions are alone or in combination with each other insufficient for obtaining the effects obtained by the chrome oxide, but they function excellent as supplements to the chrome oxide. The chrome oxide is preferably Cr2O3.

According to a further preferred embodiment of the method the further metal oxide comprises Al2O3 and the amount of Al added is ≥ 20, and preferably ≤ 300 ppm. Below 20 ppm the effect of Al2O3 added is rapidly reduced. Above 300 ppm the further positive effects of Al2O3 get marginal with the chrome oxide proportion in question.

According to a further preferred embodiment of the method the further metal oxide comprises MgO, in which the amount of Mg added is ≥ 20, and preferably ≤ 300 ppm. Below 20 ppm the positive effects of MgO upon the nuclear fuel with oxide base are reduced rapidly. Above 300 ppm Mg the further positive effects of MgO gets marginal with the chrome oxide proportion in question.

A further object of the invention is to provide a material with oxide base adapted to be sintered to a nuclear fuel element, which through a content of chrome oxide determined in advance and as a result of the composition thereof gets the advantages in the form of higher density, larger nuclear fuel grains and better plasticity resulting from the additions of said further oxides mentioned in the introduction, at the same time as a neutron absorption cross section being as low as possible is obtained for the nuclear fuel element.

This object is obtained by means of a material defined in claim 8.

A further metal oxide may be any of Nb2O5, Al2O3 and MgO already mentioned. Presence of several of these oxides jointly is also possible in the material. The further metal oxide or oxides has a supplementary object with respect to the chrome oxide, without increasing the total neutron absorption cross section of the nuclear fuel element noticeably.

According to a further preferred embodiment said metal oxide comprises aluminium oxide in the form of Al2O3, in which the amount Al is ≥ 20, and preferably ≤ 300 ppm with respect to the amount nuclear fuel. Below 20 ppm the effects of Al2O3 added are reduced. Above 300 ppm AI the further positive effects of Al2O3 gets marginal with the chrome oxide proportion in question.

According to a further preferred embodiment the metal oxide comprises magnesium oxide in the form of MgO, in which the amount Mg is ≥ 20, and preferably ≤ 300 ppm with respect to the amount nuclear fuel. The amount MgO is restricted for the same reasons as for Al2O3.

Further advantages and features of the method and the material according to the invention will appear from the detailed description following and the other dependent claims.

DETAILED DESCRIPTION OF AN EMBODIMENT

According to a preferred embodiment of the method according to the invention one or a plurality of powders comprising Cr2O3, Al2O3 and MgO is added to a powder comprising a nuclear fuel with oxide base, in this case UO2.

The amount Cr2O3 added, where Cr is in the interval 50-1000 ppm (weight proportions with respect to the weight of UO2), the amount AI added in the form of Al2O3 is in the interval 20-300 ppm and the amount Mg added in the form of MgO is in the interval 20-300 ppm. An adhesive and a lubricant are added separately or as a part of any of said powders as already known per se.

The powders are then mixed in any way known per se so that a homogenous mixture is obtained.

The homogenous powder mixture is then pressed into one or several green bodies, by a pressure of 200-700 MPa.

The green body or bodies is after that sintered in a hydrogen atmosphere with an addition of 0,1-5,0 % of CO2, as an alternative only in humidified hydrogen without an addition of CO2. The sintering lasts for 1-6 hours at a temperature of 1400-1800°C and under atmosphere pressure. A density very close to the theoretical density is obtained thereby. The UO2 grains, which at the beginning had a grain size in the order of 10 µm, have during the sintering grown to ≥ 25 µm, i.e. they have become considerably larger.

The oxides Cr2O3, Al2O3 and MgO added have during the sintering formed a liquid phase which in the material sintered and cooled, i.e. the fuel element formed, forms the matrix around the UO2-particles present in the sintered body.

Variations of the preferred embodiment described will of course be apparent to a man skilled in the art, but he will then not go around the scope of protection defined by the appended claims with support by the description of the invention.

The method and the material according to the invention are well suited for production of nuclear fuel elements in the form of fuel pellets, which are positioned in cladding tubes and are used in compressed-water reactors and boiling water reactors for extraction of nuclear energy through nuclear fission activated by neutron irradiation.

It has to be pointed out that the ppm values mentioned relate to weight metal/weight nuclear fuel with oxide base, for example weight Cr/weight UO2.


Anspruch[de]
  1. Verfahren zur Herstellung eines Kernbrennstoffelements auf Oxydbasis, bei welchem der Kernbrennstoff auf Oxydbasis mit Cr2O3 gemischt und zu einem festen Körper gesintert wird, wobei dem Kernbrennstoff auf Oxydbasis Cr mit einem Anteil von ≥50 ppm und ≤1000 ppm zugegeben wird, bezogen auf die Menge des Kernbrennstoffs auf Oxydbasis, und wobei mindestens ein weiteres Metalloxyd, dessen Metall einen wesentlich kleineren Neutronenabsorptionsquerschnitt hat als Cr, in einer solchen Menge zugegeben wird, daß es beim Sintern merklich zu der korn-vergrößernden Wirkung von Chromoxyd in dem Kernbrennstoff beiträgt.
  2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das weitere Metalloxyd Aluminiumoxyd enthält oder ist.
  3. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß das Aluminiumoxyd Al2O3 enthält oder ist und daß die Menge des zugegebenen A1 ≥20, und vorzugsweise ≤300 ppm, ist.
  4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß das weitere Metalloxyd Magnesiumoxyd enthält oder ist.
  5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, daß Magnesiumoxyd MgO enthält oder ist und die Menge des zugegebenen Mg ≥20, und vorzugsweise ≤300 ppm, ist.
  6. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß das Sintern bei einer Temperatur durchgeführt wird, bei welcher das Chromoxyd und das mögliche weitere Metalloxyd eine flüssige Phase bilden, welche nach dem Sintern eine Matrix zwischen den Partikeln des Kernbrennstoffs auf Oxydbasis bildet.
  7. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß der Kernbrennstoff auf Oxydbasis mindestens eines der Oxyde UO2, ThO2 und PuO2 enthält.
  8. Material auf Oxydbasis, welches sich zu einem Kernbrennstoffelement sintern läßt, welches einen Kernbrennstoff auf Oxydbasis und Cr2O3 enthält, wobei die Menge Cr ≥50 und ≤1000 ppm ist, bezogen auf die Menge des Kernbrennstoffs auf Oxydbasis, und wobei das Material mindestens ein weiteres Metalloxyd enthält, dessen Metall einen wesentlich kleineren Neutronenabsorptionsquerschnitt als Cr hat und in einer solchen Menge vorhanden ist, daß es beim Sintern des Materials merklich zu einer korn-vergrößernden Wirkung des Chromoxyds bei dem Kernbrennstoff auf Oxydbasis beiträgt.
  9. Material auf Oxydbasis nach Anspruch 8, dadurch gekennzeichnet, daß das weitere Metalloxyd Aluminiumoxyd enthält oder ist.
  10. Material auf Oxydbasis nach Anspruch 9, dadurch gekennzeichnet, daß das Aluminiumoxyd Al2O3 ist und die Menge des A1 ≥20 und vorzugsweise ≤300 ppm ist.
  11. Material auf Oxydbasis nach einem der Ansprüche 8 bis 10, dadurch gekennzeichnet, daß das weitere Metalloxyd Magnesiumoxyd enthält oder ist.
  12. Material auf Oxydbasis nach Anspruch 11, dadurch gekennzeichnet, daß das Magnesiumoxyd MgO ist und daß die Menge Mg ≥20 und vorzugsweise ≤300 ppm ist.
  13. Material auf Oxydbasis nach einem der Ansprüche 8 bis 12, dadurch gekennzeichnet, daß der Kernbrennstoff auf Oxydbasis mindestens eines der Oxyde UO2, ThO2 und PuO2 enthält.
Anspruch[en]
  1. A method for production of a nuclear fuel element with oxide base, in which the nuclear fuel with oxide base is mixed with Cr2O3 and sintered to a solid body, wherein Cr is added to the nuclear fuel with oxide base at a portion of ≥ 50 ppm and < 1000 ppm with respect to the amount of nuclear fuel with oxide base, and wherein at least one further metal oxide, the metal of which has a substantially smaller neutron absorption cross section than Cr, is added at such an amount that it will contribute noticeably to a grain enlarging effect of chrome oxide on the nuclear fuel in the sintering.
  2. A method according to claim 1, characterized in that the further metal oxide comprises aluminium oxide.
  3. A method according to claim 2, characterized in that the aluminium oxide comprises Al2O3 and that the amount of Al added is ≥ 20, and preferably ≤ 300 ppm.
  4. A method according to any of claims 1-3, characterized in that the further metal oxide comprises magnesium oxide.
  5. A method according to claim 4, characterized in that the magnesium oxide comprises MgO and the amount Mg added is ≥ 20, and preferably ≤ 300 ppm.
  6. A method according to any of claims 1-5, characterized in that the sintering is carried out at a temperature at which the chrome oxide and the possibly further metal oxide form a liquid phase which after the sintering forms a matrix between particles of the nuclear fuel with oxide base.
  7. A method according to any of claims 1-6, characterized in that the nuclear fuel with oxide base comprises at least one of the oxides UO2, ThO2 and PuO2.
  8. A material with oxide base adapted to be sintered to a nuclear fuel element, which comprises a nuclear fuel with oxide base and Cr2O3, wherein the amount Cr is ≥ 50 ppm and ≤ 1000 ppm with respect to the amount of the nuclear fuel with oxide base, and wherein the material comprises at least one further metal oxide, the metal of which has a substantially smaller neutron absorption cross section than Cr and is present in such an amount that it contributes noticeably to a grain enlarging effect of chrome oxide upon the nuclear fuel with oxide base at the sintering of the material.
  9. A material with oxide base according to claim 8, characterized in that the further metal oxide comprises aluminium oxide.
  10. A material with oxide base according to claim 9, characterized in that the aluminium oxide is Al2O3 and that the amount Al is ≥ 20, and preferably ≤ 300 ppm.
  11. A material with oxide base according to any of claims 8-10, characterized in that the further metal oxide comprises magnesium oxide.
  12. A material with oxide base according to claim 11, characterized in that the magnesium oxide is MgO and that the amount Mg is ≥ 20, and preferably ≤ 300 ppm.
  13. A material with oxide base according to any of claims 8-12, characterized in that the nuclear fuel with oxide base comprises at least one of UO2, ThO2 and PuO2.
Anspruch[fr]
  1. Procédé de production d'un élément combustible nucléaire ayant une base d'oxyde, dans lequel le combustible nucléaire ayant une base d'oxyde est mélangé à du Cr2O3 et fritté en un corps solide, Cr étant ajouté au combustible nucléaire ayant une base d'oxyde en une proportion ≥ 50 ppm et < 1 000 ppm par rapport à la quantité de combustible nucléaire ayant une base d'oxyde, et dans lequel au moins un oxyde métallique supplémentaire, dont le métal a une section efficace d'absorption des neutrons sensiblement plus petite que celle du Cr, est ajouté en une quantité telle qu'il contribue de manière notable'à un effet d'agrandissement des grains d'oxyde de chrome sur le combustible nucléaire dans le frittage.
  2. Procédé suivant la revendication 1, caractérisé en ce que l'oxyde métallique supplémentaire comprend de l'oxyde d'aluminium.
  3. Procédé suivant la revendication 2, caractérisé en ce que l'oxyde d'aluminium comprend du Al2O3 et la quantité d'aluminium ajoutée est ≥ 20 et de préférence < 300 ppm.
  4. Procédé suivant l'une quelconque des revendications 1 à 3, caractérisé en ce que l'oxyde métallique supplémentaire comprend de l'oxyde de magnésium.
  5. Procédé suivant la revendication 4, caractérisé en ce que l'oxyde de magnésium comporte du MgO et la quantité de Mg ajoutée est ≥ 20 et de préférence < 300 ppm.
  6. Procédé suivant l'une quelconque des revendications 1 à 5, caractérisé en ce que le frittage est effectué à une température à laquelle l'oxyde de chrome et l'oxyde métallique supplémentaire éventuel forment une phase liquide qui, après le frittage, forme une matrice entre des particules du combustible nucléaire ayant une base d'oxyde.
  7. Procédé suivant l'une quelconque des revendications 1 à 6, caractérisé en ce que le combustible nucléaire ayant une base d'oxyde comprend au moins l'un des oxydes UO2, ThO2 et PuO2.
  8. Matériau ayant une base d'oxyde conçu pour être fritté en un élément combustible nucléaire, qui comporte un combustible nucléaire ayant une base d'oxyde et du Cr2O3, dans lequel la quantité de Cr est ≥ 50 ppm et ≤ 1 000 ppm par rapport à la quantité de combustible nucléaire ayant une base d'oxyde, et dans lequel le matériau comporte au moins un oxyde métallique supplémentaire, dont le métal a une section efficace d'absorption. des neutrons sensiblement plus petite que celle du Cr et est présent en une quantité telle qu'il contribue de manière notable à un effet d'agrandissement des grains de l'oxyde de chrome sur le combustible nucléaire ayant une base d'oxyde au frittage du matériau.
  9. Matériau avec une base d'oxyde suivant la revendication 8, caractérisé en ce que l'oxyde métallique supplémentaire comprend de l'oxyde d'aluminium.
  10. Matériau avec une base d'oxyde suivant la revendication 9, caractérisé en ce que l'oxyde d'aluminium est du Al2O3 et en ce que la quantité de AI est ≥ 20 et de préférence ≤ 300 ppm.
  11. Matériau avec une base d'oxyde suivant l'une quelconque des revendications 8 à 10, caractérisé en ce que l'oxyde métallique supplémentaire comprend de l'oxyde de magnésium.
  12. Matériau avec une base d'oxyde suivant la revendication 11, caractérisé en ce que l'oxyde de magnésium est du MgO et en ce que la quantité de Mg est ≥ 20 ppm et de préférence ≤ 300 ppm.
  13. Matériau avec une base d'oxyde suivant l'une quelconque des revendication 8 à 12, caractérisé en ce que le combustible nucléaire ayant une base d'oxyde comprend au moins l'un de UO2, de ThO2 et PuO2.






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