Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
materials (boulders, sand, etc.) present at or transiting via the site zone, the morphology
of the sea or river bottom.
Mathematical models of hydrological dispersion
There is no universal model representing the dispersion of radioactive materials in all
sections of a liquid mass and for all possible situations. In most cases, the initial dilution
phase, the mixing phase, and the long distance dispersion phase are dealt with separately.
Two approaches are generally used:
Models based on simplified forms of the diffusion equation, often used far from the
points of discharge;
Compartmented models describing exchanges between boxes representing clearly
defined portions of the medium in which a homogeneous distribution of the
pollutant is assumed.
The distribution of concentrations near the point of discharge covers an extent that
depends on local conditions, i.e., in particular on the shape and dimensions of the outfall,
the discharge velocity and flow rate. It is at most a few kilometers. The corresponding
models study the dispersion of water discharged into stagnant or moving water.
Other models covering larger areas deal with the “mixing” phase, in the course of which
the initial discharge can be regarded as becoming physically impossible to distinguish
from the receiving waters. Various schematic representations are then used according to
local conditions. It may be a straight rectangular channel with flow parallel to the banks
to simulate a river; more elaborate calculations that include the advection due to the
movement of the masses of water and dispersion by wave action may be performed.
Finally, going beyond this, models of the “far” field must take account of the effects of
❙ 350 ❙