Modelling of the iodine/aerosol interaction in the atmosphere

PhD student: Camille FORTIN

Context
In the case  of a nuclear reactor accident, radionuclides can be released into the atmosphere. Some simulation tools are developed to predict their behaviour in the environment. These codes are used in an emergency case to inform populations and to take countermeasures (evacuation, prophylaxis). This approach complete the evaluation of the iodine source term due to the lack of knowledge in the case of an accidental scenario. During the Fukushima accident, the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) has conducted evaluations about the radionuclides dispersion in the environment. The caesium deposition quantity estimated by the IRSN crisis centre (C3X) was closed to the one measured by the in-situ measurement while it was not the case for iodine. This discrepancy could be explained by the chemical reactivity of iodine in the atmosphere, which was not implemented in the codes.

The gaseous phase mechanism development has shown that organic and inorganic iodine species can easily react with atmospheric particles. To have a better understanding of the iodine radiologic impact, it is necessary to take into account those interactions mainly about their impact on ozone and their radiative impact. These particles can moreover easily be inhaled and make health damages. In atmospheric sciences, the volatile species, which can react with particles, are essentially water, inorganic species (sulphate, nitrate, ammoniac), biogenic or anthropogenic organic species. The gas/particle study go through the good evaluation of the thermodynamic equilibrium between different phases. This equilibrium can be characterized by experimental data or theoretical calculations (quantum chemistry, molecular dynamics).

The purpose of this thesis is to study the interactions between iodine species and atmospheric aerosols and to add this phenomenology to the iodine dispersion model.

Director : Florent Louis (PC2A)

Co-director : Valérie Fèvre-Nollet (PC2A)

IRSN advisor : Frédéric Cousin

Laboratory : PC2A

Financing : IRSN