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  • TSPA 2002 1

    Implementation Of Colloid-Facilitated Transport in the Engineered Barrier System of the TSPA Model

    Presented by:Sunil MehtaYucca Mountain Project

    Presented at:2002 GoldSim User ConferenceApril 25-26, 2002

  • TSPA 2002 2

    Introduction

    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 3

    Introduction (continued)

    Colloid CharacterizationWaste Form colloids

    Colloids with Reversibly and Irreversibly attached RNs Most significant contributor to colloid-facilitated radionuclide

    transport 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 packages

  • TSPA 2002 4

    Implementation Requirements

    Colloid 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 5

    Implementation - 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 6

    Treatment of Irreversible species

    Irreversible Pu species:Ic234Ic237Ic238Ic239Ic240

    Irreversible Am species:Ic241Ic243

  • TSPA 2002 7

    Treatment of Irreversible species

  • TSPA 2002 8

    Decay of Irreversible species

  • TSPA 2002 9

    TSPA Implementation

  • TSPA 2002 10

    TSPA 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 11

    Colloid Mass Generation (input to Source)

  • TSPA 2002 12

    CDSP Source Inventory

    Initial mass of colloidsis set very high (unlimited inventory)

    No initial mass of Icspecies given

  • TSPA 2002 13

    Source Term Release to Waste Form Cell

    Mass released fromSource to Waste_Formcell is controlled by Glass matrix dissolution rate

    The mass of Pu and Amreleased is modified by removing the fraction bound irreversibly as colloids

  • TSPA 2002 14

    TSPA Model - Media in Cell - CDSP Package

    Colloids in CDSP Packages

    Reversible colloid component

    Irreversible colloid component

  • TSPA 2002 15

    TSPA Model - Colloid Transport Parameters

  • TSPA 2002 16

    TSPA Model - Colloid Transport

    Mass flux (g/yr) of colloids out of the Waste Form cell

    Computes Advective + Diffusive flux

  • TSPA 2002 17

    TSPA Model - Colloid Transport

  • TSPA 2002 18

    Calculation of Pu mass sorbed to WF colloid

    Concentration of Waste Form colloids with Irreversibly sorbed Pu

    Concentration based on Ionic Strength stability field

    Concentration based on pH stability field

  • TSPA 2002 19

    Calculation of Colloid Mass In a Unit Volume

    Waste Form colloid mass (g/L) available for Reversible and Irreversible sorption

    Conc. (solubility) of Irreversiblysorbed species (mg/L)

    Defines the solubility of Col species

  • TSPA 2002 20

    Species Solubility

  • TSPA 2002 21

    Calculation of Pu species concentration

    Concentration of Pu isotopes irreversiblysorbed to WF colloids-- by multiplying totalPu conc. with mole fraction

  • TSPA 2002 22

    TSPA Model - Colloid Transport

  • TSPA 2002 23

    Irreversible Colloid Mass Computation

    Computes mass of irreversible Puspecies: Minimum of

    Mass of Pu in pathway

    engthTimestep_L ssFlux Colloid_Ma Colloid of Conc.

    Pu Irrev. of Conc.

  • TSPA 2002 24

    Irreversible Colloid Mass Adjustment

    Function to adjust irreversible colloid mass from dissolved mass

  • TSPA 2002 25

    Irreversible Colloid Mass Adjustment

    Consequence element to compute discrete changes within the waste form cell

  • TSPA 2002 26

    Irreversible Colloids Logic

  • TSPA 2002 27

    Waste Form Reversible Colloid Material

  • TSPA 2002 28

    Waste Form Reversible Colloid Material

  • TSPA 2002 29

    TSPA Model - Media in Cell - CDSP Package

    Colloids in CDSP Packages

    Reversible colloid component

    Irreversible colloid component

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