Civil Engineering Reference
In-Depth Information
Fig. 20.6
Result of an Eulerian grid model calculation (JRodos screen shot)
gaseous elemental iodine with high binding capacity. For modeling v
d
, the
prevailing meteorological and flow conditions and data about the land use (urban,
agricultural, forestry areas, vegetation, types of plants, leaf sizes, etc.) is taken into
account.
Dry deposition on a given plant type is calculated with the time-integrated air
concentration close to the plant surface and a deposition rate that depends on plant
type and the seasonal development of the plant, making the resulting deposition
velocity clearly dependent on the season. The seasonal plant status is described by
the current leaf surface index that is defined as the aggregate leaf area per unit area
of soil.
The radionuclides are grouped with respect to their deposition properties: noble
gases (not depositing), aerosols (including iodine in aerosol form), and gaseous
iodine (elemental, organically bound).
20.4.2.2 Wet Deposition
Wet deposition is described by a wash-out model, which assumes that the entire
vertical volume of the radioactive cloud is washed out in the area covered by the
rain, whereby the radionuclide content gets deposited partly on the ground and
partly on vegetation or on other surfaces. The intensity of wash-out is determined
by the rain duration and intensity and by the wet deposition characteristics of the
nuclides.
When modeling wet deposition on leaf surfaces, account must be taken of the
fact that incipient rain initially increases the leaf contamination, but parts of that
