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Kinetic study of the formation, aggregation and speciation of iodine oxides (IOx) in the vessel of a nuclear reactor in a serious accident situation

Shaoliang Zhang has defended his thesis on 29th June 2012 in Marseille.

Document type > *Mémoire/HDR/Thesis

Keywords >

Research Unit > IRSN/DPAM/SEMIC/LETR

Authors > ZHANG Shaoliang

Publication Date > 29/06/2012

Summary

Within the framework of the research in the nuclear reactor safety field, the iodine oxides formation by organic iodides destruction in the containment has been studied with the means of the atmospheric chemistry field. The destruction kinetics and their activation energy of organic iodides by ·OH and ·O radical has been quantified by a Flash Photolysis system able to monitor the oxidant radicals by resonance fluorescence. Those results have been published and some of them for the first time in the literature. The mechanisms leading to the organic iodides destruction are either by a hydrogen atom abstraction, either by the formation of a complex, depending on the organic iodide involved.

 

Then, certain kinetics reactions have been updated in the IODAIR code. Other reactions have
been added based on the recent literature available. A comparison of the kinetics destruction of CH3I by ·OH and ·O with IODAIR and the global kinetics of destruction in ASTEC/IODE showed a difference of about 2 which shows the importance of these two radicals (and mainly ·O) in those destruction processes. The other main path of destruction would be by electron radiation. Other radicals like ·H and ·N would not contribute significantly to organic iodides destruction. A sensitivity analysis highlighted that organic iodides would mostly be destroyed into iodine oxides with a almost complete conversion within a few hours.

 

Finally, an atmospheric chamber has been used to quantify iodine oxides growth, density and composition. Under the conditions studied, their formation is fast. Particles sizes of about 200- 400 nm are formed within a few hours. The main parameters influencing their growth are the relative humidity and the presence of ozone (whose function is to create ·O and ·OH radicals).


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