WO1998001867A1 - Conditionnement de dechets radioactifs - Google Patents

Conditionnement de dechets radioactifs Download PDF

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Publication number
WO1998001867A1
WO1998001867A1 PCT/GB1997/001674 GB9701674W WO9801867A1 WO 1998001867 A1 WO1998001867 A1 WO 1998001867A1 GB 9701674 W GB9701674 W GB 9701674W WO 9801867 A1 WO9801867 A1 WO 9801867A1
Authority
WO
WIPO (PCT)
Prior art keywords
waste
ceramic
immobilising
phase
medium
Prior art date
Application number
PCT/GB1997/001674
Other languages
English (en)
Inventor
Ewan Robert Maddrell
Original Assignee
British Nuclear Fuels Plc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB9614026.4A external-priority patent/GB9614026D0/en
Application filed by British Nuclear Fuels Plc filed Critical British Nuclear Fuels Plc
Priority to AU31837/97A priority Critical patent/AU3183797A/en
Publication of WO1998001867A1 publication Critical patent/WO1998001867A1/fr

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Classifications

    • 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
    • G21F9/28—Treating solids
    • G21F9/30—Processing
    • G21F9/301—Processing by fixation in stable solid media
    • G21F9/302—Processing by fixation in stable solid media in an inorganic matrix
    • 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
    • G21F9/14—Processing by incineration; by calcination, e.g. desiccation

Definitions

  • the present invention relates to a ceramic material for the encapsulation of high level radioactive waste resulting from the reprocessing of irradiated nuclear fuel .
  • Vitrification has been the preferred method of encapsulating highly active wastes comprising fission products resulting from the reprocessing of irradiated fuels.
  • the method involves the incorporation of the waste within a continuous amorphous matrix.
  • waste streams which are likely to arise in the future due to developments to the so-called PUREX process (so-called Radical PUREX process) may not be suitable for containment by the vitrification technique due principally to relatively high levels of iron, chromium and zirconium which result from the non-fuel components of fuel assemblies which are also taken into solution in the envisaged new reprocessing techniques.
  • a ceramic waste immobilising medium in which waste ions from at least fission products in irradiated nuclear fuel may be dissolved in substantially solid solution form, the ceramic waste immobilising medium having a matrix comprising phases of: cubic - Zr0 2 , ; BaZr0 3 ; at least one nickel-based solid solution; and, optionally at least one of Fe 3 0 4 , FeO and a spinel- type oxide phase comprising Fe, Cr and Al in which matrix said waste ions are dissolved.
  • the waste immobilising medium may also contain some intermetallic compound phases in addition to the nickel- based phase or phases.
  • the waste element ions partition themselves to the phases having lattice sites where they are most stable.
  • Fe and Cr are contained within the cubic Fe 3 0 4 and/or FeO phase
  • Zr rare earth elements and non- recycled actinides are contained within the Zr0 2 phase
  • larger ions such as Sr, Rb and Cs are contained within the BaZr0 3 phase.
  • elements such as Mo, Sn and Ru for example will form either solid solutions with metallic Ni which is present or will form intermetallic compounds as appropriate. At least some of the Mo and Sn may also partition to a spinel phase in the matrix.
  • the content of ZrO : m the medium may be maximised as this phase is the most resistant to leaching during storage.
  • the content of the BaZr0 3 phase may be minimised as this phase is least resistant to leaching during storage.
  • the content of the BaZr0 3 may be maintained below about 15 vol% since at this level the phase becomes reticulated, le. interconnected within the matrix and leaching is facilitated. Below about 15 voi%, this phase exists in discrete sites within the matrix and, in a fully dense material, leach resistance is greatly enhanced.
  • the spinel-type oxide phase comprising Fe, Cr and Al
  • Fe-containmg phase or phases An example of this phase may be Fe1.2Cr5. 4 Al 1 . 4 O 4 .
  • This phase may also contain Mn when present.
  • compositions of the ceramic waste immobilising medium may comprise vol%: 35- 55 Zr0 2 ; 30- 50 Fe-containmg phase or phases; 5- 20 BaZr0 3 ; and, 2- 10 Ni.
  • composition of the immobilising medium according to the present invention comprises vol%: 55 Zr0 2 ; 33 Fe 3 0 4 ; 7 BaZr0 3 ; and, 5 Ni .
  • the content of the specified Fe-containmg phase or phases in the waste immobilising medium will also reduce and, snould stainless steel and Inconel be eliminated altogether, the Fe-containmg phase or phases content will also reduce to substantially zero. Therefore, to account for this eventuality, the content of the specified Fe-containmg phase or phases is made optional .
  • a method of immobilising waste from reprocessed nuclear fuel assemblies by combining said waste in a ceramic immobilising medium according to the first aspect including the steps of converting said fuel assemblies by dissolution into a liquor; forming a slurry from said liquor by mixing with a precursor material; drying said slurry; calcining said dried slurry under a reducing atmospnere; and, containing said calcined powder for storage .
  • the method of the second aspect may also include a solvent extraction step between dissolution of the waste and forming a slurry in order to remove at least U and Pu which are separately reprocesse ⁇ into new fuel for re-use in reactors. Suitable solvent extraction cycles are known to those skilled in the relevant art.
  • the remaining waste stream after the solvent extraction step contains the fission product waste which it is desired to encapsulate by the product and method of the present invention and, the inert materials resulting from the non-fuel components of the dissolved fuel assemblies.
  • the waste stream resulting from dissolution of the waste into a liquid, and which comprises mainly nitrates may be denitrated by electrochemical techniques prior to forming a slurry, le the slurry may be formed of the denitrated waste stream with the precursor material.
  • the denitrated waste stream may comprise metal oxides and hydroxides in a very fine particle size form which have been precipitated from solution during denitration.
  • the initial waste stream may comprise metal nitrates resulting from the electrochemical dissolution (ECD) of the fuel in nitric acid.
  • ECD electrochemical dissolution
  • a typical composition of a highly active waste stream resulting from fuel assembly dissolution of one tonne of uranium may comprise the following as set out in Table 1 below:
  • the relative contents of fission products will vary with the type of fuel question, le MOX will differ from U0 2 fuel and the relative ratios thereof which may be present.
  • the ceramic immobilising medium of the present invention is able to accommodate such variations.
  • the precursor material to form the slurry may be a Zr0 2 precursor material and may comprise zirconia powder per se or zirconium propoxide for example which may be added so as to eventually establish Zr0 2 as the majority ceramic matrix constituent.
  • the precursor material may also include alumina in the form of aluminium sec- butoxide for example. The purpose of forming alumina is to provide a spinel phase in the matrix to accommodate
  • Fe 2 " ions and prevent, as far as possible, the formation of FeO which is not a naturally occurring compound.
  • Naturally occurring analogues indicate stability and leach resistance.
  • the zirconia powder forming the majority of the ceramic material should be as fine as possible, finer for example than common commercially available zirconia pow ⁇ ers .
  • the particle size of the zirconia powder should preferably be less than about 10 nanometres.
  • additives may also be used according to the actual waste composition and may include one or more of: an yttrium source, for example in the form of the nitrate or a calcium source; a barium source from the hydroxide or nitrate; a pentavelent ion in the form of tantalum oxide (from tantalum ethoxide for example) and/or niobium as an oxide for example; and iron and chromium as the nitrate for example.
  • an yttrium source for example in the form of the nitrate or a calcium source
  • a barium source from the hydroxide or nitrate
  • a pentavelent ion in the form of tantalum oxide from tantalum ethoxide for example
  • niobium as an oxide for example
  • iron and chromium as the nitrate for example.
  • a significant advantage of the method of the present invention is that the two major constituents of the ceramic immobilising medium of the present invention are also major constituents of the waste stream.
  • the zirconia is in the cubic form and provides the host phase for the rare earth elements within the spectrum of fission products produced together with non-recycled actinides.
  • the specified Fe-containing phase or phases provides the host phase to immobilise the iron, manganese and chromium.
  • the barium source is provided to react with some of the zirconia to form the BaZr0 3 phase in which the larger elements such as Cs and Sr are held in solid solution.
  • the nickel containing phase or phases serves to host at least a part of the Mo, Sn and Ru.
  • the slurry is then dried by known means to form a powder which is then calcined.
  • Calcining is carried out under a reducing atmosphere, such as an argon and hydrogen atmosphere, to convert the various constituent nitrate phases or the mixed oxide and hydroxide phases from an earlier denitration step as described above, for example, principally to oxides.
  • a reducing atmosphere such as an argon and hydrogen atmosphere
  • some nitrate phases or oxide phases such as nickel nitrate or oxide will be reduced to metallic nickel.
  • the nickel originates mainly from stainless steel and Inconel (trade name) components in the fuel assemblies.
  • the metallic nickel so formed provides a host phase to Mo and Ru present in the waste stream, these elements being combined in solid solution and/or in various intermetallic phases. Whilst some of the Mo is likely to go into the metallic phase with the Ni, some may also persist as Mo 4* ions in a spinel phase.
  • Typical calcining temperatures may lie the range from about 750°C to about 1000°C.
  • the conditions of calcining should be chosen so as to ensure that a maximum of the available Mo ions partition to the Ni-based phase to eliminate formation of barium and/or caesium molybdate.
  • Metallic iron powder may optionally be added to the pre- powder after calcining to act as an oxygen getter for any residual oxygen.
  • Processing conditions should be such as to avoid the formation of barium molybdate, BaMoOfact, and caesium molybdate, Cs 2 Mo0 4 , which have relatively low leach resistance and are thus most preferably avoided.
  • Barium and caesium molybdate have been found to form whenever M0 3 has not been completely eliminated from the waste at the calcining stage. Therefore, calcining conditions are chosen such as to ensure that no residual M0 3 exists after the calcining step. Control of the reducing conditions to avoid these phases may also entail some changes to the partitioning of the elements between the host phases and to the intentional additions made so as to influence such partitioning in order to satisfy charge balancing requirements within the host phases so as to maintain electrical neutrality.
  • the calcined powder may then be treated so as to compact, densify and sinter to form a strong, substantially porosity-free, leach resistant body suitable for long term storage.
  • the powder may be compacted into individual pellets and sintered for example or may be packed into metal cans which are then themselves compacted either by hot uniaxial pressing for example or by isostatic pressing which may be either hot isostatic pressing or cold isostatic pressing followed by sintering.
  • sintering may be carried out as close as possible to full density leaving as little porosity as possible in the final material so as to enhance leach resistance as far as possible.
  • a particular advantage of the method and ceramic waste immobilising material of the present invention is that greater loadings of highly active fission product waste of up to about 1000 kg/m 3 may be achieved compared with known techniques, the total waste loading including inert material being about 4000 kg/m 3 .
  • Modern, but known, conventional reprocessing routes such as that exemplified by Applicant's THORP plant at its Sellafield site in the United Kingdom, utilising vitrification achieve waste loadings of about 700 kg/m 3 of fission products.
  • the process and waste immobilising medium of the present invention may typically achieve a waste loading of about 50 wt% but, loadings in the range from about 40 wt% to about 70 wt% depending on waste stream composition may be achieved.
  • the tin was added as the oxide. This mixture was then homogenised using a high shear mixer, and evaporated to dryness. The resulting powders were then calcined in a flowing Ar-5% H 2 atmosphere. After calcining the powders were ground in a pestle and mortar. lOg portions of the powders were mixed with 2 wt% of metallic iron, pressed into pellets and sintered in nitrogen at 1300°C for four hours. This fabrication method is not envisaged to be that which will be used in a full scale plant. The variations in lattice parameter of the cubic zirconia and BaZr0 3 phases are consistent with what would be expected from solid solution effects.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
  • Compositions Of Oxide Ceramics (AREA)

Abstract

Milieu d'immobilisation de déchets radioactifs dans une matrice céramique et son procédé de fabrication. L'immobilisation de ces déchets consiste à dissoudre des ions de déchets radioactifs provenant au moins de produits de fission de combustible nucléaire irradié, afin d'obtenir une solution sensiblement solide, le milieu d'immobilisation possédant une matrice comprenant des phases de: cubique - ZrO2; BAZrO3; au moins une solution solide à base de nickel; et, éventuellement, au moins Fe3O4 et/ou, FeO et/ou une phase d'oxyde de type spinelle contenant Fe, Cr et Al dans laquelle lesdits ions de déchets radioactifs sont dissous.
PCT/GB1997/001674 1996-07-04 1997-06-23 Conditionnement de dechets radioactifs WO1998001867A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU31837/97A AU3183797A (en) 1996-07-04 1997-06-23 Encapsulation of waste

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GBGB9614026.4A GB9614026D0 (en) 1996-07-04 1996-07-04 Encapsulation of waste
GB9614026.4 1996-07-04
GB9624473.6 1996-11-25
GBGB9624473.6A GB9624473D0 (en) 1996-07-04 1996-11-25 Encapsulation of waste

Publications (1)

Publication Number Publication Date
WO1998001867A1 true WO1998001867A1 (fr) 1998-01-15

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AU (1) AU3183797A (fr)
WO (1) WO1998001867A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2367418A (en) * 2000-08-19 2002-04-03 British Nuclear Fuels Plc Encapsulation of waste
US7078581B1 (en) 1999-11-12 2006-07-18 British Nuclear Fuels Plc Encapsulation of waste
US7241932B2 (en) * 2001-08-03 2007-07-10 British Nuclear Fuels Plc Encapsulation of radioactive waste using a sodium silicate based glass matrix

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0007236A1 (fr) * 1978-07-14 1980-01-23 The Australian National University Résidus radioactifs de haute activité immobilisés dans un assemblage minéral et procédé pour immobiliser les résidus radioactifs de haute activité
JPS5512448A (en) * 1978-07-14 1980-01-29 Tokyo Shibaura Electric Co Ceramiccsolidified radioactive waste* and manufacture thereof
JPS5642198A (en) * 1979-09-17 1981-04-20 Tokyo Shibaura Electric Co Ceramiccsolidified radioactive waste products and preparing same
JPS5642197A (en) * 1979-09-17 1981-04-20 Tokyo Shibaura Electric Co Ceramiccsolidified radioactive waste products and preparing same
EP0043643A1 (fr) * 1980-06-30 1982-01-13 Corning Glass Works Matrice de vitro-céramique pour l'incorporation de déchets radio-actifs et pour des composés contenant des fibres inorganiques et production de ces vitro-céramiques
EP0137054A1 (fr) * 1983-09-13 1985-04-17 Kernforschungszentrum Karlsruhe Gmbh Procédé pour la fabrication d'un produit de fixation de boues résiduaires nuisibles et de ciment résistant au lessivage
EP0244534A1 (fr) * 1985-11-04 1987-11-11 Australian Nuclear Science And Technology Organisation Préparation de mélanges de déchets radioactifs particulaires
JPS62276708A (ja) * 1986-05-26 1987-12-01 株式会社村田製作所 誘電体磁器組成物
JPS63235401A (ja) * 1987-03-23 1988-09-30 Natl Inst For Res In Inorg Mater ジルコニウム及び鉛を含有する誘電体粉末の製造方法

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0007236A1 (fr) * 1978-07-14 1980-01-23 The Australian National University Résidus radioactifs de haute activité immobilisés dans un assemblage minéral et procédé pour immobiliser les résidus radioactifs de haute activité
JPS5512448A (en) * 1978-07-14 1980-01-29 Tokyo Shibaura Electric Co Ceramiccsolidified radioactive waste* and manufacture thereof
JPS5642198A (en) * 1979-09-17 1981-04-20 Tokyo Shibaura Electric Co Ceramiccsolidified radioactive waste products and preparing same
JPS5642197A (en) * 1979-09-17 1981-04-20 Tokyo Shibaura Electric Co Ceramiccsolidified radioactive waste products and preparing same
EP0043643A1 (fr) * 1980-06-30 1982-01-13 Corning Glass Works Matrice de vitro-céramique pour l'incorporation de déchets radio-actifs et pour des composés contenant des fibres inorganiques et production de ces vitro-céramiques
EP0137054A1 (fr) * 1983-09-13 1985-04-17 Kernforschungszentrum Karlsruhe Gmbh Procédé pour la fabrication d'un produit de fixation de boues résiduaires nuisibles et de ciment résistant au lessivage
EP0244534A1 (fr) * 1985-11-04 1987-11-11 Australian Nuclear Science And Technology Organisation Préparation de mélanges de déchets radioactifs particulaires
JPS62276708A (ja) * 1986-05-26 1987-12-01 株式会社村田製作所 誘電体磁器組成物
JPS63235401A (ja) * 1987-03-23 1988-09-30 Natl Inst For Res In Inorg Mater ジルコニウム及び鉛を含有する誘電体粉末の製造方法

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* Cited by examiner, † Cited by third party
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DATABASE WPI Section Ch Week 8123, Derwent World Patents Index; Class K07, AN 81-41189D, XP002040602 *
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7078581B1 (en) 1999-11-12 2006-07-18 British Nuclear Fuels Plc Encapsulation of waste
GB2367418A (en) * 2000-08-19 2002-04-03 British Nuclear Fuels Plc Encapsulation of waste
US7241932B2 (en) * 2001-08-03 2007-07-10 British Nuclear Fuels Plc Encapsulation of radioactive waste using a sodium silicate based glass matrix

Also Published As

Publication number Publication date
AU3183797A (en) 1998-02-02

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