Implementation Of Colloid-Facilitated Transport in ?· Implementation Of Colloid-Facilitated Transport…

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TSPA 2002 1Implementation Of Colloid-Facilitated Transport in the Engineered Barrier System of the TSPA ModelPresented by:Sunil MehtaYucca Mountain ProjectPresented at:2002 GoldSim User ConferenceApril 25-26, 2002TSPA 2002 2Introduction Three types of colloids modeled (two mineralogies) Waste form colloids (glass-waste derived smectite assumed to behave as natural smectite colloids) Corrosion product colloids (rust; assumed to be iron oxyhydroxides) Groundwater colloids (assumed to be smectite; used as proxy for all mineral colloids present in natural groundwater) Colloid presence based on aqueous conditions Colloid concentration as f (ionic strength) Colloid stability as f (ionic strength, pH) - either maximum possible amount (stable) or ~zero amount (not stable)TSPA 2002 3Introduction (continued) Colloid CharacterizationWaste Form colloids Colloids with Reversibly and Irreversibly attached RNs Most significant contributor to colloid-facilitated radionuclidetransport Formed by nucleation of colloids from waste form dissolution and/or spallation of colloid-sized waste form alteration products Only for Co-disposal packages (not for CSNF packages)Iron (hydr)oxide and Groundwater colloids Colloids with Reversibly attached RNs only For both Co-disposal and CSNF packagesTSPA 2002 4Implementation RequirementsColloid Model Parameters in TSPA Determination of RN mass on colloids - based on ionic strength Determination of colloid stability - based on ionic strength and pH Determination of Irreversible and Reversible Partitioning of dissolved RN inventory onto colloids at each calculation time step TSPA 2002 5Implementation - Assumptions Pu, Am (and their daughter products) are irreversibly sorbed oncolloids. Pu, Am, Th (Ra, Pb), Pa (Ac) are reversibly sorbed on colloids. Radionuclide mass irreversibly sorbed on colloids will be permanently locked within the colloid for transport (ingrowth and decay considered). Colloids with irreversibly sorbed RNs can also act as sites for reversible sorption. No reversible sorption can occur until the maximum irreversible sorption to colloids is satisfied in a given time step. Irreversible attachment of Pu and Am is treated by considering them as separate species -- called Ic species.TSPA 2002 6Treatment of Irreversible speciesIrreversible Pu species:Ic234Ic237Ic238Ic239Ic240Irreversible Am species:Ic241Ic243TSPA 2002 7Treatment of Irreversible speciesTSPA 2002 8Decay of Irreversible speciesTSPA 2002 9TSPA ImplementationTSPA 2002 10TSPA Implementation In order to adjust the dissolved mass of Pu and Am, the fraction bound irreversibly must be removed from the Waste Form cell Thus the mass fraction bound irreversibly must be known But this value is not known ahead of time as irreversibly sorbedmass is a function of pH, Ionic strength, and mass in Waste Formpathway. Thus a separate calculation has to be performed, where, mass of irreversibly bound Pu and Am is computed first and then removed from the available mass in the Waste Form cell using a feed back loop. For this a fictitious species called Col was created. It is used to produce mass of colloids in the Waste Form cell based on the stability of colloids (pH and I dependent).TSPA 2002 11Colloid Mass Generation (input to Source)TSPA 2002 12CDSP Source InventoryInitial mass of colloidsis set very high (unlimited inventory)No initial mass of Icspecies givenTSPA 2002 13Source Term Release to Waste Form CellMass released fromSource to Waste_Formcell is controlled by Glass matrix dissolution rateThe mass of Pu and Amreleased is modified by removing the fraction bound irreversibly as colloidsTSPA 2002 14TSPA Model - Media in Cell - CDSP PackageColloids in CDSP PackagesReversible colloid componentIrreversible colloid componentTSPA 2002 15TSPA Model - Colloid Transport ParametersTSPA 2002 16TSPA Model - Colloid TransportMass flux (g/yr) of colloids out of the Waste Form cellComputes Advective + Diffusive fluxTSPA 2002 17TSPA Model - Colloid TransportTSPA 2002 18Calculation of Pu mass sorbed to WF colloidConcentration of Waste Form colloids with Irreversibly sorbed PuConcentration based on Ionic Strength stability fieldConcentration based on pH stability fieldTSPA 2002 19Calculation of Colloid Mass In a Unit VolumeWaste Form colloid mass (g/L) available for Reversible and Irreversible sorptionConc. (solubility) of Irreversiblysorbed species (mg/L)Defines the solubility of Col speciesTSPA 2002 20Species SolubilityTSPA 2002 21Calculation of Pu species concentrationConcentration of Pu isotopes irreversiblysorbed to WF colloids-- by multiplying totalPu conc. with mole fractionTSPA 2002 22TSPA Model - Colloid TransportTSPA 2002 23Irreversible Colloid Mass ComputationComputes mass of irreversible Puspecies: Minimum ofMass of Pu in pathway engthTimestep_L ssFlux Colloid_Ma Colloid of Conc.Pu Irrev. of Conc.TSPA 2002 24Irreversible Colloid Mass AdjustmentFunction to adjust irreversible colloid mass from dissolved massTSPA 2002 25Irreversible Colloid Mass AdjustmentConsequence element to compute discrete changes within the waste form cellTSPA 2002 26Irreversible Colloids LogicTSPA 2002 27Waste Form Reversible Colloid MaterialTSPA 2002 28Waste Form Reversible Colloid MaterialTSPA 2002 29TSPA Model - Media in Cell - CDSP PackageColloids in CDSP PackagesReversible colloid componentIrreversible colloid component


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