Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
consequences differ considerably according to the final dispersion channel into the
environment, i.e. atmospheric or water channel.
Deposition is the main phenomenon that reduces the radioactivity contained in the gas.
They depend on the form in which the fission products are found in the gas (gas, steam,
aerosols) and on the thermodynamic conditions. The main physical phenomena that affect
the fission products concentration (under aerosol physical state) in the containment are
the following: − Agglomeration and sedimentation; − Thermophoresis (temperature
gradient induced mechanism); − Diffusiophoresis (concentration gradient induced
mechanism); − Impaction; − Hygroscopicity (particle growth due to steam
condensation on it).
It was found that most of the fission product aerosols agglomerate and deposit on the
walls and floor of the containment in approximately 4 hours and from there they are
transported to the sump. Thus, they are not available for release to environment on the
failure of the containment. In this process, the more toxic fission products, i.e., 131 I and
137 Cs which had formed the highly water‐soluble compounds CsI and CsOH are
removed from the containment atmosphere when a spray action is activated. [7]
Code validation and results indicate that the aerosol behaviour itself is fairly well
understood. The main uncertainties rise from the accuracy of predicting and modelling
the prevailing thermal hydraulic and flow conditions as well as coupling aerosol
behaviour with thermal hydraulics.
Revaporization/resuspension of deposits:
These phenomena are also crucial, since it is a deferred potential source, likely to
challenge the conservatism of assessments. They depend on thermal hydraulic conditions
and on the link's strength between the deposit and the deposition surface, (therefore still
depending on the physical and chemical forms). In the deposition and revaporization/
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