GB2367418A - Encapsulation of waste - Google Patents
Encapsulation of waste Download PDFInfo
- Publication number
- GB2367418A GB2367418A GB0020404A GB0020404A GB2367418A GB 2367418 A GB2367418 A GB 2367418A GB 0020404 A GB0020404 A GB 0020404A GB 0020404 A GB0020404 A GB 0020404A GB 2367418 A GB2367418 A GB 2367418A
- Authority
- GB
- United Kingdom
- Prior art keywords
- waste
- medium
- immobilising medium
- sodium
- radioactive
- 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.)
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- 239000002699 waste material Substances 0.000 title claims abstract description 127
- 238000005538 encapsulation Methods 0.000 title description 7
- 239000000446 fuel Substances 0.000 claims abstract description 37
- 238000012958 reprocessing Methods 0.000 claims abstract description 25
- 239000003758 nuclear fuel Substances 0.000 claims abstract description 21
- 238000005253 cladding Methods 0.000 claims abstract description 15
- 239000011159 matrix material Substances 0.000 claims abstract description 15
- YHKRPJOUGGFYNB-UHFFFAOYSA-K sodium;zirconium(4+);phosphate Chemical compound [Na+].[Zr+4].[O-]P([O-])([O-])=O YHKRPJOUGGFYNB-UHFFFAOYSA-K 0.000 claims abstract description 12
- 229910052596 spinel Inorganic materials 0.000 claims abstract description 6
- 239000011029 spinel Substances 0.000 claims abstract description 6
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 claims description 32
- 238000000034 method Methods 0.000 claims description 32
- 239000011734 sodium Substances 0.000 claims description 31
- 229910019142 PO4 Inorganic materials 0.000 claims description 30
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims description 28
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 claims description 28
- 239000010452 phosphate Substances 0.000 claims description 28
- 229910052708 sodium Inorganic materials 0.000 claims description 28
- 239000000203 mixture Substances 0.000 claims description 22
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 17
- 230000004992 fission Effects 0.000 claims description 17
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 15
- 239000012857 radioactive material Substances 0.000 claims description 13
- 238000011068 loading method Methods 0.000 claims description 11
- 239000002901 radioactive waste Substances 0.000 claims description 11
- 229910052768 actinide Inorganic materials 0.000 claims description 10
- 150000001255 actinides Chemical class 0.000 claims description 10
- 229910052804 chromium Inorganic materials 0.000 claims description 9
- 239000011651 chromium Substances 0.000 claims description 9
- 229910052742 iron Inorganic materials 0.000 claims description 9
- 230000002285 radioactive effect Effects 0.000 claims description 9
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 8
- 229910052759 nickel Inorganic materials 0.000 claims description 8
- 238000001035 drying Methods 0.000 claims description 6
- 239000000463 material Substances 0.000 claims description 6
- 238000000638 solvent extraction Methods 0.000 claims description 6
- 238000001354 calcination Methods 0.000 claims description 5
- 238000005245 sintering Methods 0.000 claims description 4
- 239000011363 dried mixture Substances 0.000 claims description 3
- 238000003825 pressing Methods 0.000 claims description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 abstract description 19
- 238000004090 dissolution Methods 0.000 abstract description 5
- 235000021317 phosphate Nutrition 0.000 description 24
- 239000000047 product Substances 0.000 description 14
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 7
- 239000012071 phase Substances 0.000 description 7
- 229910052726 zirconium Inorganic materials 0.000 description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 239000000843 powder Substances 0.000 description 5
- 239000010802 sludge Substances 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- IKNAJTLCCWPIQD-UHFFFAOYSA-K cerium(3+);lanthanum(3+);neodymium(3+);oxygen(2-);phosphate Chemical compound [O-2].[La+3].[Ce+3].[Nd+3].[O-]P([O-])([O-])=O IKNAJTLCCWPIQD-UHFFFAOYSA-K 0.000 description 4
- 238000001513 hot isostatic pressing Methods 0.000 description 4
- 229910052590 monazite Inorganic materials 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 3
- KKCBUQHMOMHUOY-UHFFFAOYSA-N Na2O Inorganic materials [O-2].[Na+].[Na+] KKCBUQHMOMHUOY-UHFFFAOYSA-N 0.000 description 3
- 229910052778 Plutonium Inorganic materials 0.000 description 3
- 229910052770 Uranium Inorganic materials 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 229910001093 Zr alloy Inorganic materials 0.000 description 3
- 239000000654 additive Substances 0.000 description 3
- 238000000429 assembly Methods 0.000 description 3
- 230000000712 assembly Effects 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- OYEHPCDNVJXUIW-UHFFFAOYSA-N plutonium atom Chemical compound [Pu] OYEHPCDNVJXUIW-UHFFFAOYSA-N 0.000 description 3
- 239000002915 spent fuel radioactive waste Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- JFALSRSLKYAFGM-UHFFFAOYSA-N uranium(0) Chemical compound [U] JFALSRSLKYAFGM-UHFFFAOYSA-N 0.000 description 3
- 238000004017 vitrification Methods 0.000 description 3
- 239000004254 Ammonium phosphate Substances 0.000 description 2
- 229910052688 Gadolinium Inorganic materials 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 235000019289 ammonium phosphates Nutrition 0.000 description 2
- 229910052788 barium Inorganic materials 0.000 description 2
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 2
- 229910052792 caesium Inorganic materials 0.000 description 2
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical compound [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 238000005056 compaction Methods 0.000 description 2
- UIWYJDYFSGRHKR-UHFFFAOYSA-N gadolinium atom Chemical compound [Gd] UIWYJDYFSGRHKR-UHFFFAOYSA-N 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000010808 liquid waste Substances 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 150000002823 nitrates Chemical class 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- 229910052712 strontium Inorganic materials 0.000 description 2
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 description 2
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- STCOOQWBFONSKY-UHFFFAOYSA-N tributyl phosphate Chemical compound CCCCOP(=O)(OCCCC)OCCCC STCOOQWBFONSKY-UHFFFAOYSA-N 0.000 description 2
- 229940093635 tributyl phosphate Drugs 0.000 description 2
- 229910000148 ammonium phosphate Inorganic materials 0.000 description 1
- ZRIUUUJAJJNDSS-UHFFFAOYSA-N ammonium phosphates Chemical class [NH4+].[NH4+].[NH4+].[O-]P([O-])([O-])=O ZRIUUUJAJJNDSS-UHFFFAOYSA-N 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 239000010786 composite waste Substances 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000000284 extract Substances 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 239000002927 high level radioactive waste Substances 0.000 description 1
- 229910001026 inconel Inorganic materials 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 238000002386 leaching Methods 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 238000009376 nuclear reprocessing Methods 0.000 description 1
- OOAWCECZEHPMBX-UHFFFAOYSA-N oxygen(2-);uranium(4+) Chemical compound [O-2].[O-2].[U+4] OOAWCECZEHPMBX-UHFFFAOYSA-N 0.000 description 1
- 239000002574 poison Substances 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910001415 sodium ion Inorganic materials 0.000 description 1
- 239000004317 sodium nitrate Substances 0.000 description 1
- 235000010344 sodium nitrate Nutrition 0.000 description 1
- 239000001488 sodium phosphate Substances 0.000 description 1
- 235000011008 sodium phosphates Nutrition 0.000 description 1
- 238000003826 uniaxial pressing Methods 0.000 description 1
- FCTBKIHDJGHPPO-UHFFFAOYSA-N uranium dioxide Inorganic materials O=[U]=O FCTBKIHDJGHPPO-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
- C04B35/447—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on phosphates, e.g. hydroxyapatite
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/34—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing cold phosphate binders
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/64—Burning or sintering processes
- C04B35/645—Pressure sintering
- C04B35/6455—Hot isostatic pressing
-
- 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
- G21F9/16—Processing by fixation in stable solid media
- G21F9/162—Processing by fixation in stable solid media in an inorganic matrix, e.g. clays, zeolites
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
- C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
- C04B2235/30—Constituents and secondary phases not being of a fibrous nature
- C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
- C04B2235/3201—Alkali metal oxides or oxide-forming salts thereof
- C04B2235/3203—Lithium oxide or oxide-forming salts thereof
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
- C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
- C04B2235/30—Constituents and secondary phases not being of a fibrous nature
- C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
- C04B2235/3231—Refractory metal oxides, their mixed metal oxides, or oxide-forming salts thereof
- C04B2235/3244—Zirconium oxides, zirconates, hafnium oxides, hafnates, or oxide-forming salts thereof
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/91—Use of waste materials as fillers for mortars or concrete
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Inorganic Chemistry (AREA)
- Organic Chemistry (AREA)
- Structural Engineering (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- General Engineering & Computer Science (AREA)
- High Energy & Nuclear Physics (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Processing Of Solid Wastes (AREA)
Abstract
A means for immobilising both highly active waste and medium active waste arising from an advanced Purex reprocessing plant in which substantial amounts of the non-fuel components of a fuel assembly are also taken into solution during the head-end dissolution step comprising a sodium zirconium phosphate matrix, wherein there is distributed in the matrix a spinel phase comprising at least elements from dissolved nuclear fuel cladding and fuel assembly components.
Description
ENCAPSULATION OF WASTE
The present invention relates to an immobilising medium for the encapsulation of radioactive waste resulting from the reprocessing of irradiated nuclear fuel and a method for preparing the same.
Nuclear reprocessing plants use the well-established Purex process. These plants produce both highly active (HA) wastes and medium active (MA) wastes. By HA waste is generally meant the bulk of the fission products with associated material from irradiated nuclear fuel. By MA waste is generally meant materials e. g. fuel cladding which have gained a substantial measure of radioactivity by contact with the fuel proper or by exposure to the neutron flux but do not generate significant heat levels.
The conventional Purex process involves stripping the cladding from the fuel rod or leaching the fuel from inside and then dissolving the spent fuel. The uranium and plutonium from the spent fuel is then separated from the minor actinides and fission products by solvent extraction. The HA wastes comprise the minor actinides and fission products separated from the spent fuel. MA wastes typically comprise the remains of the stripped or leached nuclear fuel cladding as well as contaminated filters and other contaminated components of fuel assemblies.
In addition, phosphate containing effluents from the operations using tributylphosphate (tbp) solvent during nuclear fuel reprocessing and sodium containing effluents which may arise from the use of solvent cleaning chemicals such as NaOH in the reprocessing plant may be classed as MA waste.
Vitrification has been the preferred method of encapsulating
HA wastes. The method involves the incorporation of the waste within a continuous amorphous matrix. Encapsulation in cement has to date been the preferred method of encapsulating MA wastes.
However, waste streams which are likely to arise in the future due to developments to the so-called Purex process (so-called
Advanced 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.
An envisaged Advanced Purex process employs a different headend process to conventional Purex, i. e- the process of separating the cladding from the fuel and converting the fuel into a form suitable for chemical separation. The general scheme of an envisaged Advanced Purex head-end process and its waste arisings is shown schematically in Figure 1. The whole fuel assembly including stainless steel structural components, cladding and fuel rods is subjected to a nitric acid dissolution step 1 as opposed to just the fuel in conventional
Purex. This results in large amounts of iron, nickel, chromium and zirconium in the HA solution in addition to the usual actinides and fission products (FP). About 15% of the
Zircaloy (trade mark) fuel cladding and most of the stainless steel and Inconel (trade mark) components are taken into solution along with the irradiated fuel. The remainder of the
Zircaloy is left as a slightly oxygen deficient MA zirconia sludge. This sludge is separated and treated as MA waste 4.
The HA solution is then subjected to solvent extraction 3 to separate the uranium and plutonium from the waste actinides, fission products, iron, nickel, chromium and zirconium which are routed to the HA waste stream S.
An advanced Purex reprocessing plant will also produce MA liquid wastes containing significant quantities of sodium and phosphate. MA waste streams containing sodium, e. g. as sodium nitrate, may arise as a result of using solvent cleaning chemicals such as NaOH in the reprocessing plant. MA waste streams containing phosphate may arise from operations using tributylphosphate (tbp) solvent during nuclear fuel reprocessing. These MA waste streams thus form part of the overall MA waste from the plant 4.
In conventional oxide fuel Purex reprocessing the HA waste consists predominantly of fission products and is immobilised within a vitrified matrix at a waste loading of 20-25 wt%.
The high level waste produced by more modern and improved
Advanced Purex reprocessing routes, however, contains such high quantities of inert material from the fuel assembly that vitrification at the same waste loading would roughly quadruple the volume of HA waste produced per tonne of fuel reprocessed.
It is therefore desirable to be able to accommodate higher loadings of active waste into the immobilising medium so as to minimise the volume of the final immobilised waste.
Whilst technologies exist to treat the HA and MA streams separately, it may be convenient to immobilise both the HA wastes and MA wastes arising from an Advanced Purex reprocessing plant in a composite waste form to which all waste and effluent streams could be routed. This has the advantages that the plant only produces a single form of waste and thus two different types of encapsulation lines are not required.
According to a first aspect of the present invention there is provided a waste immobilising medium in which highly radioactive waste is contained, the waste immobilising medium comprising a sodium zirconium phosphate matrix, wherein there is distributed in the matrix a spinel phase comprising at least elements from dissolved nuclear fuel cladding and fuel assembly components.
A typical stoichiometry of the sodium zirconium phosphate is
NaZr2 (PO4) 3. The sodium zirconium phosphate typically comprises around 80 % of the immobilising medium. The sodium zirconium phosphate is preferably wholly crystalline.
The waste immobilising medium may contain an approximate molar ratio of Na/P = 1/4.
The sodium zirconium phosphate matrix efficiently acts as an host for highly radioactive elements, for example the fission products and actinide elements. For example, caesium, barium and strontium may be dissolved in the sodium zirconium phosphate. Caesium may replace Na in the matrix. Strontium or barium may replace two Na ions in the matrix to ensure neutrality.
The waste immobilising medium is highly durable and leach resistant and is suitable for long term storage of radioactive waste.
The waste immobilising medium is for containing combined HA and MA waste from an advanced Purex reprocessing plant.
The waste immobilising medium enables a high waste loading of up to about 70 weight % to be achieved.
The radioactive waste comprises at least elements from dissolved nuclear fuel assembly components and fuel cladding and fission products and other radioactive species from irradiated nuclear fuel.
The elements from dissolved nuclear fuel cladding and fuel assembly components typically comprise iron, nickel and chromium and zirconium. Thus the spinel phase is formed of at least some of the iron, nickel and chromium.
The other radioactive species from irradiated nuclear fuel may comprise actinide elements.
There may also be present a monazite phase formed between rare earth elements and phosphate.
The waste is a combination of HA waste and MA waste streams arising from advanced reprocessing plant utilising an electrochemical dissolution head-end process.
The fission products and other radioactive species from irradiated nuclear fuel are predominantly derived from the highly radioactive waste material which arises from the solvent extraction cycle in reprocessing which extracts the uranium and plutonium. A minor proportion of the fission products and other radioactive species from irradiated nuclear fuel are derived from a medium active waste.
Advantageously, the waste itself provides all of the zirconia to form the sodium zirconium phosphate. Zirconia is typically present in HA and MA wastes from advanced reprocessing in high amounts from Zircaloy (trade name) fuel cladding.
As described above, an advanced Purex reprocessing plant produces medium active liquid wastes containing significant quantities of sodium and phosphate. The immobilising medium also makes use of MA waste containing sodium and phosphate to provide preferably all of the sodium and at least some of the phosphate used to form the sodium zirconium phosphate
Overall, HA wastes containing fission products, iron, chromium, nickel and zirconium and MA wastes containing zirconium, phosphate and sodium are combined and encapsulated in one immobilising medium by the present invention, the zirconium, phosphate and sodium being used to form in part the immobilising medium.
The waste immobilising medium may achieve a waste loading of up to about 70 weight % waste. Waste loading is defined as the mass of waste/total mass of waste immobilising medium, which is the same as mass of waste/ (mass of waste + mass of additives).
Such a high waste loading is possible because of the use of zirconia, sodium and phosphate from the waste to form the main phases of the immobilising medium. Maximising the waste loading and thereby minimising the final volume of the waste form is one of the key aims of any new waste form.
The volume of the final immobilised waste form according to the present invention is typically about 0.25 m3 per tonne of reprocessed fuel.
Combining all the waste in one immobilising medium according to the present invention means that the overall process for waste encapsulation is simpler as two separate encapsulation methods for HA and MA waste are not required.
According to a second aspect of the present invention there is provided a method of preparing a waste immobilising medium according to the first aspect of the invention, the method including the steps of forming a mixture comprising highly radioactive material, zirconia, phosphate and sodium; drying the mixture; calcining the dried mixture; and pressing and sintering the calcined mixture.
Preferably, the amounts of phosphate and sodium are adjusted so that the final waste immobilising medium has an approximate molar ratio of Na/P = 1/4.
The highly radioactive material results from the dissolution of fuel assemblies, cladding and fuel in an Advanced Purex reprocessing scheme as described above.
The highly radioactive material is a combination of HA and MA waste streams from an Advanced Purex reprocessing plant.
The highly radioactive material comprises minor actinides and fission products separated from irradiated nuclear fuel by reprocessing.
The highly radioactive material substantially comprises the HA waste material produced by the solvent extraction cycle of reprocessing as represented by step 3 in Figure 1.
The highly radioactive material also comprises in a minor amount the small amount of highly radioactive material present in a MA waste.
The highly radioactive material is typically provided in the form of a waste liquor. The waste liquor comprises a combination of HA and MA waste streams. The waste liquor thus typically comprises substantial amounts of iron, nickel and chromium resulting from dissolution of the fuel assembly and cladding in the Advanced Purex process.
The waste liquor typically contains substantial amounts of zirconia sludge (step 2 in figure 1). The waste liquor preferably also contains phosphate and sodium. Thus, the waste liquor may provide some of the zirconia, phosphate and sodium for forming the sodium zirconia phosphate matrix of the waste immobilising medium. The waste liquor may provide all of at least one of the zirconia and sodium.
Supplementary amounts of sodium and phosphate may be added.
Typically only phosphate will need to be added to the waste liquor in substantial amounts. This is so that the amounts of the sodium and phosphate are adjusted to enable a sodium zirconium phosphate matrix to be formed in the final waste immobilising medium having a sodium and phosphate composition of about 20 mol% Na20 and about 80 mol% P205.
Where the waste itself comprises zirconia, phosphate and sodium, the proportions of waste to the supplementary amounts of phosphate and/or sodium are such that a waste loading of typically 70 weight% may be achieved in the final immobilising medium.
The phosphate and sodium may be added as P205 and Na20.
Preferably, sodium and ammonium phosphates may be used as additives.
In addition to fission product and actinide elements, the waste liquor may contain gadolinium from its use as a neutron poison in the fuel.
In the waste liquor many of the highly active waste elements may be present in the form of nitrates because of the use of nitric acid in the reprocessing operations
Preferably, the waste liquor is denitrated before or whilst forming the mixture. This makes further processing of the waste liquor easier. If the liquor is not denitrated, an undesirable sludge or paste may be formed in the mixture which may be difficult to dry effectively.
The denitration may be performed in one of many ways. A preferred method of denitration comprises reacting the liquor with formaldehyde. After denitration, the liquor remains as a substantially liquid phase.
Mixing of the components in the mixture is effected typically by stirring. Stirring ensures homogeneity in the mixture.
Other methods of homogeneously mixing may be used.
After the mixture has been formed and sufficiently mixed, the mixture is dried. The drying may be carried out by one of many methods known to the person skilled in the art. For example drying may be effected on a hot plate or similar apparatus.
After the mixture has been dried, it is calcined to form a powder. The calcination may be carried out in a neutral (e. g. with N2 gas) or reducing atmosphere. The reducing atmosphere may comprise an Ar/H2 mixture or a N2/H2 mixture. The hydrogen is typically diluted to 10% or less in the inert gas. For example, a 5% mixture of H2 in N2 may be used.
The calcination may be carried out between 650-800oC.
Typically, about 750oC may be used.
Optionally, the calcined powder, particularly powder calcined in an N2/H2 mixture, may be mixed with an oxygen getter prior to compaction and sintering. The oxygen getter may be a metal. For example, metallic titanium is an effective getter.
Where a metal getter is used, e. g. titanium, it may be present in the powder in an amount of, for example, about 2 wt%.
Finally, the calcined powder is compacted and sintered to produce the final immobilising medium suitable for long term storage.
The compaction and sintering may be carried out according to known methods such as Hot Uniaxial Pressing or Hot Isostatic
Pressing (HIP). HIP is preferred. Preferably the temperature for HIP is 1000-1400 C. More preferably the temperature for
HIP is 1100-1300oC.
Specific embodiments of the present invention will now be described by way of example and with reference to Figure 1 which shows an X-Ray Diffraction (XRD) pattern of a sample of a waste immobilising medium according to the present invention. The embodiments are illustrative only and do not limit the invention in any way.
Example 1
The compositions of various envisaged wastes are given below in Table 1. They simulate the waste arisings for one tonne of nuclear fuel being reprocessed in an advanced Purex reprocessing plant and contain substantial amounts of zirconia, phosphate and sodium.
TABLE I
WASTE AND EFFLUENT ARISINGS PER TONNE FUEL*
HA WASTE OXIDES HBU MOX 3: 1 mix HBU: MOX Fission 58. 2 57. 7 58. 1 Products Gadolinium 9. 1 9. 1 9. 1 Fe2O3 63.8 63.8 63.8 Cr20321. 021. 0'21. 0 NiO 19.5 19.5 19. 5 ZrOz49. 9 49. 9 49. 9 MoOs 0. 8 0. 8 0. 8 SnO2 0.8 0.8 0.8 Actinides 2. 2 6. 6 3. 3 MA WASTE OXIDES 2rO2 as 287. 5 287. 5 287. 5 Zirconia sludge Phosphate as 20 20 20 P205 Sodium as Na2O 35 35 35 HBU = High Burn Up uranium dioxide fuel
MOX = mixed oxide fuel * all values in kg
A waste immobilising medium was prepared as follows using a simulated waste from reprocessing of 3: 1 HBU: MOX mixed fuel as listed in the last column of Table 1 having a burn-up of 55GMd/te (GWd/te = giga watt days per tonne).
The oxides of the waste elements were then obtained by denitrating solutions of the corresponding nitrates as described.
Additional P205 as ammonium phosphate was added to the waste solution after the denitration but before drying (to ensure homogeneous mixing) in the following amount per one tonne fuel reprocessed.
Additives per tonne fuel reprocessed: P205 300.0 kg
Batches were prepared corresponding to 1/2000th of the waste arisings per tonne.
After drying, the dried mixture was divided into two portions before calcination. The two portions were then each calcined
at 750oC for 4 hours. One portion was calcined in flowing nitrogen, the other in flowing nitrogen/5% hydrogen. The gas flow rate was about 1 litre/minute.
The calcined mixtures were then ball milled to break down coarse aggregates and then they were hot isostatically pressed at 1200oC and a pressure of 200 Mpa for 4 hours.
The pressed waste forms were then decanned and characterised by X-ray diffraction (XRD).
An XRD pattern is shown in Figure 2. Figure 2 also shows the theoretical peak positions calculated for given phases as indicated by reference numerals 1 and 2. The theoretical peaks fit well with the experimental data. The data shows the presence of phases which match theoretical peaks for sodium zirconium phosphate (NaZr2 (PO4) 3), nichromite (NiCr204), and monazite (NdPO4). It should be noted however that neither the spinel/nichromite or monazite phases will be exactly the same as these compositions. The spinel will in practice be (Fe, Cr, Ni) 304 and the monazite will contain some of all of the rare earth elements.
Claims (18)
- Claims 1. A waste immobilising medium in which highly radioactive waste is contained, the waste immobilising medium comprising a sodium zirconium phosphate matrix, wherein there is distributed in the matrix a spinel phase comprising at least elements from dissolved nuclear fuel cladding and fuel assembly components.
- 2. A waste immobilising medium as in claim 1 wherein fission products and other radioactive species from irradiated nuclear fuel are dissolved in the matrix.
- 3. A waste immobilising medium as in claim 1 or 2 wherein the Na/P molar ratio is 1: 4.
- 4. A waste immobilising medium as in any one of claims 1 to 3 wherein the elements from dissolved nuclear fuel cladding and fuel assembly components comprise iron, nickel and chromium.
- 5. A waste immobilising medium as in claim 2 wherein the other radioactive species from irradiated nuclear fuel comprise actinide elements.
- 6. A waste immobilising medium as in any one of claims 2 to 5 wherein the fission products and other radioactive species from irradiated nuclear fuel are predominantly derived from a highly radioactive waste material produced by a solvent extraction cycle in reprocessing.
- 7. A waste immobilising medium as in any one of claims 1 to 6 wherein a minor proportion of the fission products and other radioactive species from irradiated nuclear fuel are derived from a medium active waste.
- 8. A waste immobilising medium as in any one of claims 1 to 7 wherein at least some of the zirconia, sodium or phosphate of the sodium zirconia phosphate matrix originates from the radioactive waste.
- 9. A waste immobilising medium as in any one of claims 1 to 8 wherein the waste loading is about 70 weight % waste or less.
- 10. A waste immobilising medium as in claim 1 and substantially as herein described.
- 11. A waste immobilising medium substantially as herein described with reference to the examples.
- 12. A method of preparing a waste immobilising medium as in claims 1 to 11, the method including the steps of forming a mixture comprising highly radioactive material, zirconia, phosphate and sodium; drying the mixture; calcining the dried mixture; and pressing and sintering the calcined mixture.
- 13. A method of preparing a waste immobilising medium as in claim 12 wherein a radioactive waste liquor provides the highly radioactive material and a substantial amount of the zirconia, phosphate and sodium.
- 14. A method of preparing a waste immobilising medium as in claim 12 or 13 wherein the highly radioactive material is predominantly derived from a highly radioactive waste material produced by a solvent extraction cycle in reprocessing.
- 15. A method of preparing a waste immobilising medium as in claim 14 wherein the highly radioactive material also comprises a minor amount of highly radioactive material from a medium active waste.
- 16. A method of preparing a waste immobilising medium as in any one of claims 12 to 15 wherein the radioactive waste is eventually contained in the waste immobilising medium at a 70 weight% loading or less.
- 17. A method of preparing a waste immobilising medium substantially as herein described with reference to the examples.
- 18. A method of preparing a waste immobilising medium as in claim 12 and substantially as herein described.
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| GB0020404A GB2367418A (en) | 2000-08-19 | 2000-08-19 | Encapsulation of waste |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2841897A1 (en) * | 2002-07-08 | 2004-01-09 | Rousselot Sas | Production of apatitic cement useful for trapping pollutants comprises reacting dicalcium phosphate dihydrate with calcium carbonate in the presence of an activator |
| FR2841896A1 (en) * | 2002-07-08 | 2004-01-09 | Rousselot Sas | Production of apatitic cement useful for trapping pollutants comprises reacting dicalcium phosphate dihydrate with calcium carbonate in the presence of an activator |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1998001867A1 (en) * | 1996-07-04 | 1998-01-15 | British Nuclear Fuels Plc | Encapsulation of waste |
| WO1999060577A1 (en) * | 1998-05-18 | 1999-11-25 | The Australian National University | High level nuclear waste disposal |
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2000
- 2000-08-19 GB GB0020404A patent/GB2367418A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1998001867A1 (en) * | 1996-07-04 | 1998-01-15 | British Nuclear Fuels Plc | Encapsulation of waste |
| WO1999060577A1 (en) * | 1998-05-18 | 1999-11-25 | The Australian National University | High level nuclear waste disposal |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2841897A1 (en) * | 2002-07-08 | 2004-01-09 | Rousselot Sas | Production of apatitic cement useful for trapping pollutants comprises reacting dicalcium phosphate dihydrate with calcium carbonate in the presence of an activator |
| FR2841896A1 (en) * | 2002-07-08 | 2004-01-09 | Rousselot Sas | Production of apatitic cement useful for trapping pollutants comprises reacting dicalcium phosphate dihydrate with calcium carbonate in the presence of an activator |
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| GB0020404D0 (en) | 2000-10-04 |
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