EP1088314A1 - Evacuation des dechets fortement nucleaires - Google Patents

Evacuation des dechets fortement nucleaires

Info

Publication number
EP1088314A1
EP1088314A1 EP99921989A EP99921989A EP1088314A1 EP 1088314 A1 EP1088314 A1 EP 1088314A1 EP 99921989 A EP99921989 A EP 99921989A EP 99921989 A EP99921989 A EP 99921989A EP 1088314 A1 EP1088314 A1 EP 1088314A1
Authority
EP
European Patent Office
Prior art keywords
mineral
assemblage
crystals
mineral assemblage
closely related
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP99921989A
Other languages
German (de)
English (en)
Inventor
David John Ellis
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Australian National University
Original Assignee
Australian National University
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
Application filed by Australian National University filed Critical Australian National University
Publication of EP1088314A1 publication Critical patent/EP1088314A1/fr
Withdrawn legal-status Critical Current

Links

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

Definitions

  • This invention relates to the treatment and disposal of high level radioactive wastes (HLW) from nuclear reactors, and in particular relates to a mineral assemblage incorporating HLW, to a process for producing such a mineral assemblage and to a process for immobilisation of HLW in a mineral assemblage which will retain dangerously radioactive isotopes in the waste for periods sufficient to ensure that they do not re-enter the biosphere prior to their effective decay.
  • HLW high level radioactive wastes
  • HLW such as spent fuel from nuclear reactors, as are used in commercial power plants, contains a wide range of highly radioactive isotopes. These radioactive isotopes emit radiation which is dangerous to living organisms and must be disposed of in such a manner that they do not re-enter the biosphere during their effective decay periods.
  • One group of these isotopes is formed by the fission of uranium (and plutonium). From the disposal point of view the most important components formed by such fission are 137Cs, 90Sr and the radio-active isotopes of the actinide elements.
  • the fission products 137Cs and 90Sr have half lives of about 30 years and must be contained for a period of about 600 years before they decay to safe levels.
  • the dominant radioactive species in the waste are the actinide elements, principally isotopes of Pu, Am, Cm and Np which decay by the emission of alpha particles.
  • the activity of the waste becomes comparable to that of the original uranium which was mined to produce the nuclear fuel. This is usually taken to be a suitable time for containment.
  • Spent fuel rods are generally reprocessed to recover plutonium and unused uranium. During this reprocessing the spent fuel rods are placed in cooling ponds for several years to permit the decay of several highly radioactive, short-lived fission products. Subsequently, the rods are chopped into sections and dissolved in nitric acid. Plutonium and uranium are recovered from the solution, the remainder of which is a HLW solution. In most cases these HLW solutions are transformed initially into a solid, insoluble form. This is accomplished in the first instance by evaporating the HLW solution to dryness and calcining the material to produce a fine-grained mixture of radioactive oxides-called "calcine" . Calcine is an unsatisfactory form for disposal because of its low density, low thermal conductivity and high solubility. Thus, further processing of this material is necessary for its safe disposal.
  • a synthetic rock known as SYNROC is described for example in United States Patent No. 4,274,976.
  • the SYNROC materials are a mineral assemblage containing well formed crystals capable of providing lattice sites in which the elements of the HLW are securely bound.
  • the crystals belong to or possess crystal structures closely related to at least two of the titanate mineral classes selected from the group consisting of perovskite (CaTiO 3 ), zirconolite (CaZrTi 2 O 7 ) and hollandite-type (BaAl 2 Ti 6 O 16 ) mineral classes.
  • SYNROC materials have been extensively investigated and are predicted to provide stable immobilisation of HLW elements, allowing the assemblage to be safely buried in an appropriate geological environment. Consequently, SYNROC materials are in the process of commercial development for the storage of HLW wastes.
  • the extensive investigations into the SYNROC materials has led to the incorporation of rutile, and often with a small percentage of titanium metal. It has been reported that the preferred formulations of SYNROC have been designed to avoid destabilisation and incorporate an excess of rutile TiO 2 such that rutile is the major phase of the SYNROC assemblage.
  • SYNROC assemblages are preferably formulated with substantial amounts of rutile in order to improve stability, rutile plays little or no part in taking up the HLW.
  • the present invention is directed to an alternate assemblage which does not contain significant quantities of rutile.
  • mineral assemblages which include calzirtite provide at least a useful alternative to the previously disclosed SYNROC compositions.
  • this invention provides a mineral assemblage comprising crystals belonging to or possessing crystal structures closely related to both the perovskite and zirconoUte mineral classes and further comprising crystals belonging to or possessing crystal structures closely related to the calzirtite mineral class wherein the mineral assemblage incorporates high-level radioactive wastes immobilized therein.
  • a mineral complex which forms part of a mineral assemblage is generally qualified by the term "crystals belonging to or possessing crystal structures closely related to " .
  • This term will be understood by those skilled in the art to refer not only to the mineral complex having an ideal crystal structure but also to mineral complexes incorporating additional elements therein, such as elements replacing one or more of the elements of the ideal crystal structure or additional elements retained interstitially within the ideal crystal structure.
  • the additional elements may give rise to a departure of the crystal structure from the ideal.
  • Perovskite is a complex of calcium and titanium oxides having an ideal formulation CaTiO 3 .
  • Perovskite-type structures are adopted by ABO 3 compounds such as CaTiO 3 perovskite.
  • the ideal CaTiO 3 component is of orthorhombic symmetry.
  • Zirconolite is a complex of calcium, titanium and zirconium oxides having an ideal formula CaZrTi 2 O 7 .
  • Zirconolite may be more generally described as CaZr x Ti 2 . x O 7 and is a generic term to encompass a group of closely related structural polytypes which occur in monoclinic, trigonal and orthorhombic polytypes.
  • Calzirtite is a complex of calcium, titanium and zirconium oxides having an ideal formula Ca 2 Zr 5 Ti 2 O 16 .
  • Calzirtite may be more generally described as Ca 2 Zr 5 .
  • x Ti x O 16 is a generic term to encompass a group of closely related structural polytypes. Both calzirtite and zirconolite are anion deficient fluorite-related superstructure phases.
  • the cations occupy fluorite-type positions in the tetragonal cell.
  • the mineral assemblages of the present invention preferably comprise crystals of mineral complexes which are relatively small in size, in order to maximise diffusion controlled uniformity of HLW incorporation into desired crystalline structures.
  • the crystals of the mineral assemblages are generally of up to two hundred microns in size.
  • titanium in the crystal structures of the crystals of the mineral assemblages of the present invention where the titanium is of at least two different co-existing valency states permits a more stable immobilization of the radioactive isotopes of the HLW within the mineral assemblage.
  • Ti 3+ and Ti 4+ is particularly preferred.
  • Ti 2 O 3 may be present in solid solution in the crystals of the mineral assemblage.
  • Mineral complexes incorporating other elements may advantageously be incorporated into the mineral assemblages of the present invention. It is preferred that mineral complexes which incorporate barium and/or aluminium be incorporated into the mineral assemblages. Hollandite of general composition AJB y Cg. y O,,;, ideal end member (BaAl 2 Ti 6 O 16 ) is particularly preferred as a host phase for HLW elements together with perovskite, zirconolite and calzirtite. Under certain conditions of production, other Ba, Al phases may also occur. The presence of these elements and crystal structures is particularly preferred for hosting certain HLW elements, which otherwise do not readily partition into the other phases. Other hollandite-type mineral complexes which may be included within the mineral assemblages include K and Sr replacing Ba.
  • the assemblage includes at least some of each of the calzirtite, zirconolite, perovskite and hollandite. More preferably, the assemblage includes at least 10 weight percent of each of calzirtite, zirconolite, perovskite and hollandite.
  • the mineral assemblages may include at least 20 weight percent HLW.
  • the present invention also provides a process for immobilizing high level radio-active waste comprising the steps of:
  • the high level radio-active waster calcine is generally formed from a solution of HLW such as may be produced from commercial nuclear power plants.
  • the calcine may typically be formed by evaporating the solution of HLW to dryness and calcining the material to form a fine-grained mixture of radio-active oxides.
  • the composition of a typical HLW calcine resulting from the fission of uranium (and plutonium) is set our in table 1 below: TABLE 1
  • HLW elements may be incorporated into this mineral assembly by adding an HLW calcine mixture prior to heating.
  • the HLW calcine may make up, up to about 20% by weight of the mixture of oxides.
  • the oxides may be mixed by any convenient means and heated by processes as are known to those skilled in the art.
  • the oxides are selected, having regard to their composition and their relative proportions so as to form the desired mineral assemblage.
  • the oxides and amounts will be in part dependent upon the processing conditions and it will be apparent to those skilled in the art how to make such selections in order to obtain the mineral assemblages hereinabove described.
  • Oxides which may be used in the process of the present invention include CaO, ZrO 2 , TiO 2 , TiO 2 - Ti 2 O 3 solution, Al 2 O 3 and BaO, oxides, carbonates, gels or glasses.
  • the heating can be to either subsolidus or above solidus conditions. Heating to above solidus conditions may allow the mineral assemblage to be produced in less time.
  • a mineral assemblage is preferably formed by heating the mixture of oxides to subsolidus conditions.
  • the formation of the mineral assemblage under subsolidus conditions requires the mixture be maintained at an elevated temperature, say 1000 to 1600°C for a period sufficient for the mineral assemblage to achieve phase equilibrium and have the crystals of the desired particle size.
  • the preferred time of heating varies with temperature. It can be at a temperature of 1000°C for 36 hours or up to a temperature of 1600°C for one four as well as intermediate temperatures and heating times to produce desirable results. It is then allowed to cool to ambient temperature.
  • the assemblage of this invention can be formed under pressure of one atmosphere or by using hot isostatic pressing techniques.
  • a reducing environment is preferably used for the incorporation Ti in a number of different valency states. This can be achieved by several methods under appropriate reducing atmospheric conditions. One approach is to take TiO 2 and under appropriate atmosphere convert it into a Magnelli phase with the desired Ti 4+ -Ti 3+ solid solution. This is then added to the other oxides prior to synthesis. Another approach is to add Ti 4+ directly to the other oxides and convert some of it into Ti 3+ prior to heating (with or without Ti metal).
  • Figure 1 shows a molecular proportion phase diagram which illustrates the mineral assemblages of the present invention. Mineral assemblages according to this invention are within the area bordered by the lines respectively joining points marked as calzirtite, zirconolite and perovskite. The assemblages may also include hollandite (Ba Al 2 Ti 6 O 16 ). Previous SYNROC compositions have fallen into the area bounded by the lines connecting zirconolite, rutile and perovskite.
  • Figure 2 shows a molecular proportion phase diagram which incorporates Ti.
  • the mineral assemblages which include perovskite, zirconolite and calzirtite may also include Ti 2 O 3 in solid solution, in the absence of rutile.
  • the mineral assemblages according to the present invention contain a number of coexisting titanate and hollandite-type phases, in which calzirtite, zirconolite, perovskite and preferably a Ba-phase such as hollandite are prevalent. Other Ba-phases as well as baddeleyite, srilankite may occur under certain conditions. These phases, when synthesised under appropriate conditions, substitute HLW elements into their crystalline structures by a variety of substitution mechanisms. This results in significant departure from ideal end member compositions. Without wishing to be bound by theory, it is believed that the HLW elements are immobilized in a number of coexisting minerals which depart from ideal compositions due to their abilities to accommodate HLW elements into their crystalline structures.
  • the mineral assemblages of the present invention is believed to incorporate significant HLW components through a variety of substitutions for Ca, Zr, Ti, Ba, Al in the various crystal structure sites.
  • Certain HLW elements partition differently into the different phases, based on crystal chemical principles. These substitutions range from simple replacements (one element for another) through to coupled substitutions such that several HLW elements replace several element on different crystallographic sites in the ideal crystal structures.
  • both Ca and Ti may be substituted to varying amounts by certain HLW additive elements. This may be by either element-element replacements (for example Ca replaced by Sr) or else more coupled substitutions involving rare earth elements, U, Na) as well as Ti 3+ . These substitutions can result in symmetries other than orthorhombic (such as cubic, rhombohedral).
  • HLW elements such as rare earth and actinide elements may be accommodated within the structure.
  • the mixture was heated in a metal vessel at a temperature of 1300°C for 6 hours and allowed to cool to ambient temperature.
  • the resultant mineral assemblage had the following crystals present in the proportions listed below:
  • the mixture was heated in a metal vessel at a temperature of 1300°C for 6 hours and allowed to cool to ambient temperature.
  • the resultant mineral assemblage had the following crystals present in the proportions listed below:

Landscapes

  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
  • Processing Of Solid Wastes (AREA)

Abstract

L'invention concerne des déchets fortement radioactifs pouvant être immobilisés dans des assemblages de minéraux contenant peu ou pas de rutile. L'assemblage minéral comprend des cristaux appartenant à ou possédant des structures cristallines très proches des minéraux de la classe de la pérovskite et zirconolite et comprenant aussi des cristaux présentant des structures cristallines très proches de des minéraux de type calzirtite. Cet assemblage renferme des déchets fortement radioactifs.
EP99921989A 1998-05-18 1999-05-18 Evacuation des dechets fortement nucleaires Withdrawn EP1088314A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
AUPP3555A AUPP355598A0 (en) 1998-05-18 1998-05-18 High level nuclear waste disposal
AUPP355598 1998-05-18
PCT/AU1999/000376 WO1999060577A1 (fr) 1998-05-18 1999-05-18 Evacuation des dechets fortement nucleaires

Publications (1)

Publication Number Publication Date
EP1088314A1 true EP1088314A1 (fr) 2001-04-04

Family

ID=3807808

Family Applications (1)

Application Number Title Priority Date Filing Date
EP99921989A Withdrawn EP1088314A1 (fr) 1998-05-18 1999-05-18 Evacuation des dechets fortement nucleaires

Country Status (5)

Country Link
EP (1) EP1088314A1 (fr)
JP (1) JP2002516397A (fr)
AU (1) AUPP355598A0 (fr)
CA (1) CA2332842A1 (fr)
WO (1) WO1999060577A1 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB9926674D0 (en) 1999-11-12 2000-01-12 British Nuclear Fuels Plc Encapsulation of waste
GB2367418A (en) * 2000-08-19 2002-04-03 British Nuclear Fuels Plc Encapsulation of waste
US8754282B2 (en) * 2011-06-02 2014-06-17 American Isostatic Presses, Inc. Methods of consolidating radioactive containing materials by hot isostatic pressing

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4274976A (en) * 1978-07-14 1981-06-23 The Australian National University Treatment of high level nuclear reactor wastes
US4329248A (en) * 1979-03-01 1982-05-11 The Australian National University Process for the treatment of high level nuclear wastes
US5656009A (en) * 1995-08-11 1997-08-12 Battelle Memorial Institute Process for immobilizing plutonium into vitreous ceramic waste forms
US5597516A (en) * 1995-08-11 1997-01-28 Battelle Memorial Institute Process for immobilizing plutonium into vitreous ceramic waste forms

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9960577A1 *

Also Published As

Publication number Publication date
JP2002516397A (ja) 2002-06-04
CA2332842A1 (fr) 1999-11-25
AUPP355598A0 (en) 1998-06-11
WO1999060577A1 (fr) 1999-11-25

Similar Documents

Publication Publication Date Title
EP0007236B1 (fr) Résidus radioactifs de haute activité immobilisés dans un assemblage minéral et procédé pour immobiliser les résidus radioactifs de haute activité
McMaster et al. Radionuclide disposal using the pyrochlore supergroup of minerals as a host matrix—A review
AE et al. The SYNROC process: A geochemical approach to nuclear waste immobilization
McCarthy High-level waste ceramics: materials considerations, process simulation, and product characterization
Vance Synroc: a suitable waste form for actinides
Vance et al. Incorporation of radionuclides in crystalline titanates
US4329248A (en) Process for the treatment of high level nuclear wastes
Raison et al. Zirconia-based materials for transmutation of americium and curium: Cubic stabilized zirconia and zirconium oxide pyrochlores
Shoup et al. Novel plutonium titanate compounds and solid solutions Pu2Ti2O7‐Ln2Ti2O7: relevance to nuclear waste disposal
Ringwood et al. Immobilization of high-level waste in ceramic waste forms
Stefanovsky et al. Characterization of modified murataite based ceramics as a perspective hosts for actinides, fission, and corrosion products of HLW
Matzke et al. Incorporation of transuranic elements in titanate nuclear waste ceramics
Ishida et al. Leaching behavior of crystalline phosphate waste forms
WO1999060577A1 (fr) Evacuation des dechets fortement nucleaires
Burakov et al. Behavior of 238 Pu-doped ceramics based on cubic zirconia and pyrochlore under radiation damage
Yudintsev et al. Phase distribution of uranium in matrices for immobilization of the rare earth–actinide fraction of high-level waste
AU3921699A (en) High level nuclear waste disposal
Hartmann et al. Fabrication and chemical durability of ceramic technetium-based pyrochlores and perovskites as potential waste forms
Burakov et al. Development of crystalline ceramic for immobilization of TRU wastes in VG Khlopin Radium Institute
Kinoshita Development of ceramic matrices for high level radioactive wastes
Balmer et al. The structure and properties of two new silicotitanate zeolites
Gong et al. Zirconia–a ceramic for excess weapons plutonium wastes
Raison et al. Fundamental aspects of Am and Cm In Zirconia-based materials: investigations using X-ray diffraction and Raman spectroscopy
US7148394B2 (en) Ceramic for packaging of radioactive cesium
Vance et al. Studies of pollucite

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 20001120

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AT DE FR GB IT SE

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 20031202