PhD contract (M/F). Experimental approach to the mechanisms of selenium incorporation in aluminoborosilicate glasses: Application to the immobilisation of 79Se radioisotopes.

Job Description

Thesis Subject

Experimental approach to the mechanisms of selenium incorporation in aluminoborosilicate glasses: Application to the immobilisation of 79Se radioisotopes.
Selenium-79 is a by-product of nuclear power plant activity. Although produced in small quantities, it poses a serious environmental problem due to its long half-life (0.28 Ma), high mobility in the environment and high volatility at high temperature, which prevents the use of a standard vitrification protocol for long-term immobilisation.
As part of the ADAM&EVE project, we propose an experimental protocol using high-pressure conditions to circumvent the problem of Se volatility and allow for increased incorporation into the glass matrix. Currently, the behaviour of Se in glass matrices is almost unknown. There is only one study that investigates the local environment of Se at extremely low concentrations in nuclear glasses. Preliminary tests show that we are able to produce matrices with much higher Se concentrations. Under these conditions, the behaviour of Se is unknown.
During this thesis work, we will first synthesise glass matrices under variable pressure conditions (0.25-1.5 GPa) and for variable compositions ranging from the most polymerised to the most depolymerised in order to determine the most suitable matrix formulation for immobilising selenium. Next, we will test different forms of selenium, ranging from Se metal to a more oxidised form (SeO2). The materials produced will be characterised by XPS spectroscopy to determine the speciation of Se. We plan to obtain access to synchrotron radiation for X-ray absorption experiments, which will complement this method, and finally we plan to perform NMR analyses by enriching our samples with 77Se.
In the second part of the thesis, we will characterise the matrices produced by NMR in order to determine the impact of Se incorporation on the glass structure. It should be noted that we have considerable expertise in this field, particularly on the impact of pressure on glass structures. We will be able to gain a more detailed understanding of the impact of Se and, in this case, on the chemical durability of the matrices produced. This approach involves analysing local environmental changes for the cations forming the framework (e.g. B, Al and Si) and also the associated anions (e.g. the different types of oxygen present in the structure).
Finally, we will focus on the evolution of the physical properties of materials, with particular emphasis on the impact of selenium on the mechanical strength of matrices, which is an important parameter in the long-term immobilisation of nuclear waste storage matrices. At this stage, it will be interesting to link our observations at the atomic scale with the analysis of macroscopic properties.
All of these results will contribute to our fundamental understanding of the behaviour of selenium incorporated into glass matrices, with a view to developing a future experimental protocol for the immobilisation of 79Se that is industrially feasible.
Applications must include two PDF files:
1) A PDF file containing a full and up-to-date CV.
2) A PDF file containing the following: - A cover letter. - Two letters of recommendation, at least one of which must be written by the supervisor of your Master's thesis. - Proof of your academic results in the form of official transcripts.

Your Work Environment

The Laboratoire de Planétologie et Géosciences (LPG – UMR 6112) is a multidisciplinary research unit established in 2000 and spread across three sites: the Nantes Université, the Angers Université and the Université of Le Mans. The LPG is a major player at both national and international level in the field of Earth and Space Sciences. The laboratory's research covers a very broad disciplinary spectrum, currently organised around three themes. Its research forms part of past, present and planned international space missions to the rocky and icy bodies of the solar system. On Earth, research covers geosciences in the broadest sense, ranging from the Earth's interior and surface (imaging, observations, analyses and modelling in the fields of geophysics, geochemistry and digital science) to environmental and palaeoenvironmental themes, employing experimental approaches in the laboratory and numerous field and marine missions. The post is based at the LPG's Nantes site. This site is home to around 85 of the Unit's staff, out of a total of 130. The successful candidate will be integrated into the LPG's “Terre” research theme and will work in collaboration with the various LPG members involved in the ADAM&EVE project. In addition, close collaboration will be required with members of the Institut des Matériaux de Nantes Jean Rouxel.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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