Influence of redox conditions on iodine dissolution mechanisms in borosilicate glasses: Experimental and spectroscopic approaches



Three keywords: Environment, Nuclear waste, Iodine radioisotope

Research unit : Laboratoire de Planétologie et Géodynamique – UMR CNRS 6112

Name of the thesis director: MORIZET Yann
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Name of the thesis co-supervisor 1 (if applicable): PARIS Michael
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Thesis grant (funding origin and amount): Doctoral school

Contact(s) (mailing address and E-mail): Yann Morizet LPG UMR CNRS 6112 Bât. 4 Faculté des Sciences et Techniques 2 rue de la Houssinière – BP92208 44322 Nantes Cedex3 (France)



The 129I radioactive isotope is a by-product of nuclear plants activity and is considered as the radioactive dose contributor in natural geological system. Owing to its volatility and strong mobility in environment; it cannot be immobilized using the standard protocol of glass synthesis at ambient pressure. Considering that this radioisotope can fix in living organisms, it represents an immediate environmental and societal risk. Consequently, there is a need for immobilizing this element in the most adequate matrix. The IPress PhD project proposes an innovative experimental approach aiming at entrapping iodine in glass matrix synthesised under high pressure and high temperature. Our preliminary study suggests that this protocol is efficient in immobilizing iodine radioisotope.

Research will concentrate on the determination of the solubility laws and the incorporation mechanisms for iodine as a function of intensive conditions and in particular the change in redox conditions as iodine presents several oxydation states (-1 to +7). The effect iodine on the local structure of glasses will be determined as it represents a proxy for glass stability that is an crucial parameter for determining the possibility for natural geological disposal of such I- bearing matrices.

The main steps of the thesis and scientific procedure

- Bibliographical study to understand and define in detail the scientific problem and to apprehend the use of analytical tools and the processing of the obtained data

- Sample preparation and syntheses under extreme conditions

- Sample characterization using state-of-the-art analytical techniques: Solid-State NMR, X-ray Photoelectron Spectroscopy, Raman spectroscopy

- Modelling of the iodine solubility as function of intensive conditions (pressure, temperature and redox conditions) - Constraints on the effect of iodine on glass local structure

Methodological and technical approaches considered

- Experimental approach under high pressure and high temperature conditions in piston-cylinder (LPG) - Change in redox conditions using various sources of iodine: NaI, I2, I2O5, Na(IO4)
- I speciation determination using XPS
- I effect on glass structure via NMR using isotopically enriched samples

Scientific and technical skills required by the candidate

- An experience on NMR spectroscopy is desired
- Knowledge of amorphous/vitreous systems, inorganic chemistry, and thermodynamics is preferred - A spirit of synthesis and enthusiasm in lab work
- Undeniable writing skills in French and English