1. Radionuclide transport modelling
Igor Brovchenko, Vladimir Maderich,
Institute of Mathematical Machine and System Problems, National Academy of Sciences of Ukraine, Ukraine
K.T.Jung, K.O.Kim
Korea Institute of Ocean Science and Technology, South Korea

2. Main applications of SELFE/SCHISM: Sediment transport (Yellow Sea)
Radionuclide transport (Fukushima)
Stratified flows (Weddel Sea)
Lagrangian particle tracking models:
Oil spills
Sediments
Radionuclides

3. Model of radionuclide transport

4. Observed vertical profiles of 137Cs in bed sediments around the Fukushima NPP
Closest to NPP point
Black, Buesseler 2014

5. Observed vertical profiles of 137Cs in bed sediments around the Fukushima NPP
February 2012
July 2012
Ambe et. al. 2014

6. Multylayer bed sediment and radionuclide model

7. Tortuosity factor can be related with porosity of medium
Tortuosity is the ratio of the length of the curve (L) to the distance between the ends of it (A-B)
Tortuosity factor can be related with porosity of medium
Boudreau, 1997

8. Radioactivity model equations in water column
- dissolved radionuclide in water, Bq/m3
- particulated radionuclide on i-th suspended sediments, Bq/m3
- settling velocity of i-th suspended sediments, m/s
- concentration of suspended sediments, kg/m3
- distribution coefficient between dissolved and particulated phases
- desorption rate, 1/s

9. Governing equation for the bed sediments
Upper layer thickness:
Upper layer fractions:
Upper layer porosity:
Lower layers fractions
And porosity:
-bed layer thickness
-mass fraction of sediment of class I in the bed layer j
-porosity in the layer j

10. Radionuclide transport model equations for bed layers

11. Exchange between water column and bottom sediments
Shaw and Hanratty (1977)
is Schmidt number, u* is friction velocity
Exchange rate corrected for rough bottom
is Reynolds number

12. Migration of radionuclides in bed sediments in laboratory experiment
Concentration profiles
in pore water
Concentration profiles in sediments
J. Smith et. al. 2000

13. Channel flow morphology processes
Cs inflow = 1.e+6Bq/m3, for t<14days
Cs inflow = for t > 14days
Scenarios:
One fraction of sediments, no erosion-deposition
One fraction of sediments, erosion- deposition
Three fractions of sediments, no erosion-deposition
Three fraction of sediments, erosion- deposition

14. Simulation of one- and three-fraction scenarios
SSC
Particulate
Dissolved
One fraction with erosion
Three fractions with erosion

15. Bed surface layer concentration and inventory along the channel

16. Vertical profiles of concentration in locations along the channel

17. Application for the Fukushima Daichi NPP accident
Forcing used in numerical simulations:
Open boundary: global HYCOM (UV,TS,El)
Tides: NAO99 database
Meteo: Era-Interim (temperature, wind, cloudiness, humidity, pressure)
Period of simulation: 1 Jan 2011 – 30 Jun 2011

18. Scenario of direct and atmospheric release
Atmospheric deposition
Direct release

19. Comparison of dissolved 137Cs with TEPCO measurements

20. Evolution of bottom inventory
April 1
April 6
April 11
April 21
May 1
May 11

21. Evolution of bottom contamination profiles
sediments
pore water

22. Evolution of bottom contamination profiles
sediments
pore water

23. Evolution of total inventories calculated by one-layer and multilayer models

24. Conclusions
A new 3D radioactivity transport model coupled with multiscale circulation and multifractional sediment transport modules is developed
Simulation of radionuclide migration in bed sediments is in good agreement with laboratory experiment
Redistribution of radionuclide between different fractions of sediments is far slower (10 days for 137Cs) than between water and the total concentration in the sediment (several minutes).
It was shown that multi multifractional sediment and multilayer bed representation is very important on the example of contamination in channel with depression.

26. Mutual adjustment of the concentration of radioactivity in the pore water and in the mutifraction sediment
The difference between the concentration of radioactivity in the sediment fraction
and the total concentration in the sediment:
Concentration in the pore water tends to the equilibrium with
characteristic time of several minutes
Redistribution of the radioactivity between fractions is much
slower, with characteristic time 10 days.

27. One-layer model of bed sediment contamination
Equilibrium pore water
concentration

28. Idealized case of contamination of a single sediment layer by water through a diffusion mechanism

29. Radionuclide transport model equations for upper bed layer

30. Bioturbation rate j j+1 If uniform -decay of bioturbation with depth
-biodiffusion coefficient in layer j

31. A hypothetical time-series record of the concentration of a solid or solute species at a chosen point in a bioturbated sediment
Bernard P. Boudreau “Diagenetic Models and Their Implementation: Modelling Transport and Reactions in Aquatic Sediments” (1997)

32. Profiles of the apparent Kd calculated for the experiment J. Smith et
Profiles of the apparent Kd calculated for the experiment J. Smith et. al. 2000
Kd slowly approaches to the equilibrium value 2 m3/kg

33. Standard diagenetic equations
Boudreau, 1997

34. Types of advection in the bed sediments
Burial and compaction. Burial – moving of the sediment-water interface. Compaction – closer packing of sediment particles, caused by the weight of the overlying sediment column with expulsion of porewater.
Externally impressed flow. Pressure driven underground flows
Biological advection
Boudreau, 1997

35. Diffusion fluxes Boudreau, 1997 a. Molecular and Ionic Diffusion
b. Hydrodynamic dispersion
Boudreau, 1997
c. Bioturbation – biological mixing
Diffusive models and non-local models

36. Models of sorption/desorption
Borretzen, Salbu, 2002

37. Comparison of total inventory with Black&Buesseler 2014 measurements