ULB 2009-2010 Nuclear Fuel Cycle Nuclear Fuel reprocessing Sellafield - UK.

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Transcript of ULB 2009-2010 Nuclear Fuel Cycle Nuclear Fuel reprocessing Sellafield - UK.

  • Nuclear Fuel reprocessingSellafield - UK

  • Nuclear fuel reprocessingWhy reprocess?

    Basic principles

    Description of PUREX process

    Industrial status

  • Reprocessing objectivesRecycling of fissile materials (U, Pu),

    Reduction of U needs)

    Reduction of high level waste volumes

    Reduction of radiotoxicity and heat from the waste

  • The Reprocessing-RecyclingNote: message AREVA

  • Fissile materials recyclingSpent UOX fuel (33 GWj/t, cooling 3 years)

  • Spent fuel composition

  • La radiotoxicit des dchets

  • Arguments against reprocessingTechnological difficulty and large investments

    Large, generally export, reprocessing costs

    Accumulation of Pu: recycling need

    Nuclear proliferation need

    Transports of nuclear materials

  • Le retraitement du combustible irradiWhy reprocess?

    Basic principles

    Description of PUREX process

    Industrial status

  • Reprocessing functionsSeparation from spent fuel of U, Pu, and Fission Products (FP)+ Minor Actinides (MA)

    Purification of U and Pu, to be re-used

    Concentration of FP + MA for final geological disposal

  • Developed by Oak Ridge National laboratory (ORNL) and Knolls Atomic Power Laboratory (KAPL) from 1949 to 1960

    Solvent extraction based on TBP

    Targeted for separation of U and Pu

    Used on an industrial scale in Savannah River & Hanford (USA, past), La Hague (F), Sellafield (UK), Rokkashamura (J)

    PUREX: Plutonium Uranium Refining by EXtraction

  • UP3 La Hague plant*

  • Nitric acidDue to various oxidation states of N, allows the change of actinides valences

    Not too corrosive, formation of soluble metal nitratesStability in nitric acid medium: UVI NpV and NpVI PuIV and PuVI AmIII

    Recycling of vapours in nitric acid (2NO+O2 N2O4 +H2O)

  • U chemical propertiesElectronic configuration: [Rn]5f3 6d1 7s2

    6 extractible valence electrons: U metal oxidises easily in humid or hot air

    Complex chemistry (5f electrons): oxidation levels III to VI

    Level VI most stable (uranyle UO22+ in solution)

    Uranyle nitrate solubility in various organic compounds

  • Plutonium chemical propertiesElectronic configuration: [Rn]5f6 6d0 7s2

    Reuslts from neutronic irradiation of U

    Mix of several isotopes: 238, 239, 240, 241, 242

    Oxydation levels III to VII

    Levels III and IV in industrial processes

    Final reprocessing product: PuO2

  • Physico-chemical aspects (1)Fuel rods/assemblies mechanical shearing (3-4 cm slices)

    Fuel dissolution in boiling nitric acid (2h)

    UO2 + 4HNO3 UO2 (NO3)2 + 2NO2 + 2H2OUO2 + 3HNO3 UO2 (NO3)2 + 0,5NO2 + 0,5 NO + 1,5H2O

    Nitrates: Pu (NO3)4, PF (NO3)3, MA(NO3)3

    Structural materials conditioning (high activity solid waste)

    Nitrous vapours treatment

    Volatile and gaseous FP treatment

  • Physico-chemical aspects (2)TBP: organic compound forming complexes with metal (M) nitrates, not soluble in water

    Maqx- + xNO3aq- + y TBPorg [M(NO3)x y TBP]orgFormation of complexe controled by concentration in ions NO3-

    Increase NO3- favours extraction of M in organic phase

    Decrease NO3- favours re-extraction of M in aqueous phase

  • (C4H9)3PO4 or PO(OC4H9)3

    Low solubility in aqueous phase

    Affinity for U VI and Pu IV (selectivity)

    Good chemical resistance to radiolysis

    Density: 0.973 gcm-3 ; if 30% diluted: 0.83 gcm-3TBP = tri-butyl phosphateTwin free oxigen electrons

  • UO2 + 2 NO3 + 2TBP = UO2(NO3)2.2TBPThe distribution coefficient (cofficient de partage) D is the ratio of the concentration in the aqueous and organic phase: Distribution coefficient

  • Distribution coefficient

  • Extraction ability

    ClassAbility to form complexes with TBPExtraction ability A) UO2+, PuO22+, Pu4+, U4+, Zr4+, Ce4+, RuNO23+Relatively highVery good to goodB) Pu3+, Y3+, Ce3+LowLow to very lowC) Other FPsVery low to nilAlmost nil

  • TBPHNO3Spent fuelU PuFissionproductsMinor actinidesXe, Kr, I2PUREX PrincipleTBP en solution dans hydrocarbure (30%)EmulsionTransfert de matiresMlangeDcantation

  • Separation U - PuPu4+ extracted with U (class A)

    Pu3+ class B : low ability to form complexes

    Mixing of organic phase with aqueous solution, containing a selective Pu reductor (concentration NO3- must be sufficient to keep U in organic phase)

    During emulsion of the phases, Pu is reducted and goes in the aqueous phase -

  • Purification U and PuImpureties: FPs of class A

    Extraction ability lower than U and Pu, depending on [U] and [nitric acid]

    High [U]: mitigates FPextraction

    High acidity: decreases Ru extractionincreases Zr, Sr extraction

    Successive washing of organic phase

    Concentration NO3- variable, but sufficient pour hinder the re-extraction of U and Pu!

  • TBP separation basic principles Slectivity of TBP (UVI and PUIV)

    Importance of acidity: to extract UVI and PuIV: 2-3 mol/l

    To de-extract UVI:

  • Le retraitement du combustible irradiWhy reprocess?

    Basic principles

    Description of PUREX process

    Industrial status

  • ShearingDissolutionClearingExtractionPurificationSpent fuelUPuStructural elements HullsFission products & MAInsoluble residuesVitrificationGasesGasesAtmospheric or sea releasePUREX: Plutonium URanium EXtraction

  • http://www.ricin.com/nuke/bg/lahague.htmlThe La Hague reprocessing scheme

  • Spent fuel assemblies storage pool at Sellafield (UK)**

  • Shearing of cladding

  • Rotatif Dissolver

  • Caracteristics of the dissolution solution Composition: U: 200 250 g/L Pu: 2 3 g/L FP: 80% of inventory MA: 100%

    Specific activity : 7,4 TBq/L (200Ci/L)

    Nitric acidity : 3 4 M

    Oxidation state of oxides: VI, PuIV, NpV, AmIII, CmIII

  • Extraction cycles in a reprocessing plant (example)Decontamination separation cycle

    M Extraction in organic phaseAcid washing of the organic phasePu Separation (reducing re-extraction)U Re-extraction in aqueous phase

    U purification cycles (2x)

    New U extraction in organic phaseWashingU re-extraction in aqueous phase

    Pu purification cycles (2x)

    Solution oxidation (Pu4+)New Pu extraction in organic phasePu re-extraction in reducing aqueous phase

  • Feed(aq)Product(org)Waste(aq)Fresh solvent(org)Fresh solventAqueous feedLoaded solvent meets most concentrated aqueous solution Fresh solvent meets depleted aqueous solution Counter current: maximising loading & extraction

  • Feed(aq)Product(org)Waste(aq)cfcpcwFresh solvent(org)c = 01inMulti-stage extraction

  • Solvent extraction devices

  • Solvent extraction devices

  • Laboratory scale centrifugal contactors (ITU)

  • Pulsed Column

  • Solvent extraction devices

  • Recovery rate and decontamination factor Residual materials recovery rate: Pu:99,88%

    Decontamination factor: Impureties in inlet product divided by impureties in outlet product

    , impurities: U: 1,5 106; Pu: 7 107

    Separation factor U-Pu: 106

  • Technological constraints of reprocessing** High activities

    Heat release

    Under-criticity to be guaranteed, verifications

    Corrosion resistance (stainless steels, zirconium)

    Maintenance of equipement

    Controls of materials fluxes

  • U and Pu conditioningAqueous solution of Uranyl nitrate [UO2 (NO3)2] at 250 300 g U / l

    Denitration and transformation into UO3 or UO2 (fabrication plant)

    Aqueous solution of Pu nitrate: [Pu (NO3)2] at 50-150 g Pu / l

    Oxidation of Pu in Pu 4+, mixing to oxalic acid which precipitates Pu as oxalate

    Calcination and storage of PuO2 or transport to MOX plant

  • Plutonium Conversion : calcination

  • High decontamination factors

    High selectivity for U and Pu

    Low cost

    Easy scale up

    Room temperature processRadiolytic degradation of organic phase

    TBP not incinerable yielding solid radioactive waste

    Some fission products are not (fully) soluble (Zr, noble metals particles)

    Pure plutonium producedAdvantages and disadvantages of PUREX

  • Bitumen: e.g. for residues from evaporation or spent organic ion exchangers

    Cement: for low radioactive waste

    Glass: for high level liquid waste

    Ceramics: alternatives for HLLW (not industrial)

    Waste forms

  • Borosilicate glass matrix

    HLW concentrate is calcined

    Mixed with glass frit and heated at 1100 oC

    Liquid poured in a stainless steel canister

    Canister is welded shutVitrification of HLW

  • Silica is the main glass-forming component Boron oxide reduces thermal expansion and improves chemical durability

    Vitrification of HLW

    Concentration (wt%)

    R7/T7

    (Cogema)

    Magnox

    (BNFL)

    SiO2

    47.2

    47.2

    B2O3

    14.9

    16.9

    Al2O3

    4.4

    4.8

    CaO

    4.1

    -

    MgO

    -

    5.3

    Na2O

    10.6

    8.4

    Others

    18.8

    17.4

  • Vitrification of HLW

  • Waste treatment

  • Le retraitement du combustible irradiWhy reprocess?

    Basic principles

    Description of PUREX process

    Industrial status

  • Reprocessing cap