Prediction of the migration of several radionuclides in ocean sediment with the computer code IONMIG: a preliminary report Page: 12 of 19
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For all elements, except iodine, it is assumed that the molecular diffu-
sion coefficient is 0.01 m2/year (3.0 E - 10 m2/s), longitudinal dispersivicy
factor is 6.1 m,+ the transverse dispersivity factor is 0.61 m, the porosity of
the sediment is uniform and equal to 0.75. For iodine, the molecular diffusion
coefficient is 0.018 m2/year. Values for the equilibrium partition coefficient,
Kd, were obtained by fitting a limited amount of laboratory data, and were
approximated as follows:
Plutonium: Kd = +3EC + 0.01
Cesium: xd =1 + 1000 C + 0.1
Iodine and Technetium: K 1 0.0001
where C is the fluid ionic concentration in kg/m3 (Kd -alues are in a /kg; to
obtain ml/g multiply by 1000). Valence states of Cs and Pu are assumed to be
+1 and +4, respectively.
The fluid properties useJ by the code MARIAB to calculate the connective
velocities vary with temperature and plots of these quantities are shown in
Figure 5. A nominal fluid density of 1000 kg/m3 was used. Additional sediment
property values used in the MARIAH calculations are:
Density = 2950 kg/m3
Specific Heat = 880 J/kg C
Thermal Conouctivity = 1.92 exp(-6.376 E-6 T) W/m C
Porosity = 0.8
Horizontal Permeability = 5 x 10-16 m2
Vertical Permeability = 5 x 10- m2
This conservative overestimate of dispersivity factor is used because good
data is not currently available, and the low velocities calculated make
dispersion very small compared to molecular diffusion so that errors in this
factor do not affect the results.14
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Russo, A.J. Prediction of the migration of several radionuclides in ocean sediment with the computer code IONMIG: a preliminary report, report, May 1, 1980; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1056769/m1/12/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.