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UFD_DECAY

The UFD Decay Process Model is formally documented here.

Specifies the isotope decay, ingrowth, and phase partitioning model.

Required Cards:

ELEMENT <string>

Opens the block for defining elements, where <string> is the name of the element.

SOLUBILITY <float>

Specifies the solubility of the element in units of [M].

KD <float>

Opens a block where linear Kds are entered for each material property (see example below). It is assumed that all elemental isotopes sorb at the same rate, in units of [kg-water/m3-bulk].
MATERIAL_PROPERTY clay
...
MATERIAL_PROPERTY sand
...
ELEMENT Am
  SOLUBILITY 3.39d-7 ! [M]
  KD
    clay 6.d6
    sand 6.d4
  /
/

ISOTOPE <string>

Specifies each isotope, where <string> is the isotope name. The following required blocks:

ELEMENT <string>

Specifies the name of the element (group) to which the isotope belongs.

DECAY_RATE <float>

Specifies the first-order decay rate in units [1/sec].

DAUGHTER <string> <float>

Gives the name of the daughter isotope and the unitless stoichiometry of contribution to that daughter isotope.
ISOTOPE Am241
  ELEMENT Am
  DECAY_RATE 5.08d-11 ! [1/sec]
  DAUGHTER Np237 1.d0
/

Optional Cards:

IMPLICIT_SOLUTION

Applies an implicit solution approach for the decay of isotopes.

How to set up an input file:

  1. Add necessary PRIMARY_SPECIES and kinetic MINERALS to the input deck. The name of each mineral must be the same as the name of the primary species with (s) appended (e.g. I129 and I129(s)). Blocks for MINERAL_KINETICS must be included with a rate constant of 0.d0. See example:
PRIMARY_SPECIES
  I127
  I129
  Am241
  ...
  Th232
/

MINERALS
  I127(s)
  I129(s)
  Am241(s)
  ...
  Th232(s)
/

MINERAL_KINETICS
  I127(s)
    RATE_CONSTANT 0.d0
  /
  I129(s)
    RATE_CONSTANT 0.d0
  /
  Am241(s)
    RATE_CONSTANT 0.d0
  /
  ...
  Th232(s)
    RATE_CONSTANT 0.d0
  /
/
  1. Within the CONSTRAINTS, ensure that species concentrations are specified for all primary species (and minerals if the constraint is used in an initial condition). See example:
CONSTRAINT initial
  CONCENTRATIONS
    I127    1.d-20 F
    I129    1.d-20 F
    Am241   1.d-20 F
    ...
    Th232   1.d-20 F
  /
  MINERALS
    I127(s)   1.d-4 1.d0
    I129(s)   0.d0  1.d0
    Am241(s)  1.d-4 1.d0
    ...
    Th232(s)  0.d0  1.d0
  /
/
  1. Outside the SUBSURFACE/END_SUBSURFACE blocks, add a UFD_DECAY block that lists all elements and isotopes. Each element has a name (the root of the isotope; e.g. I for I127, Th for Th232), solubility, and Kd. Each isotope has a name, element, decay rate, daughter name and daughter stoichiometry (assuming a decay daughter product exists). See example:
UFD_DECAY
  ELEMENT I
    SOLUBILITY 1.d4
    KD
      sand 0.d0 ! kg water/m^3 bulk
    /
  /
  ELEMENT Am
    SOLUBILITY 3.39d-7
    KD
      sand 6.d6
    /
  /
  ...
  ELEMENT Th
    SOLUBILITY 7.94d-11
    KD
      sand 2.5d6
    /
  /
  ISOTOPE I127
    ELEMENT I
    DECAY_RATE 0.
  /
  ISOTOPE I129
    ELEMENT I
    DECAY_RATE 1.29d-15
  /
  ISOTOPE Am241
    ELEMENT Am
    DECAY_RATE 5.08d-11
    DAUGHTER Np237 1.d0
  /
  ...
  ISOTOPE Th232
    ELEMENT Th
    DECAY_RATE 1.56d-18
  /
END
  1. Include UFD_DECAY as a process model in the SIMULATION block. See example:
SIMULATION
  SIMULATION_TYPE SUBSURFACE
  PROCESS_MODELS
    SUBSURFACE_FLOW flow
      MODE TH
      OPTIONS
        MAX_PRESSURE_CHANGE 1.d8 #Pa
        MAX_TEMPERATURE_CHANGE 1.d0 #deg. C
      /
    /
    SUBSURFACE_TRANSPORT transport
      GLOBAL_IMPLICIT
    /
    UFD_DECAY ufd_decay
    /
    WASTE_FORM wf_general
      TYPE GENERAL
    /
    UFD_BIOSPHERE bio
    /
  /
END