Director(s): Olivier Pluchery, Christian Grisolia (CEA, co-directeur)
Funding:
Description :
Start: 2017
End: 2020
PhD Sudent :Samuel Peillon
Team(s): Chemical Physics and Dynamics of Surfaces  
Teams' Page of thesis : Chemical Physics and Dynamics of Surfaces  
Thesis status: Thesis defended

Abstract

The mobility and containment of radioactive dust produced by plasma/wall interactions taking place in the heart of a tokamak have become, over the years, major topics for the safety assessment of the ITER installation. Under normal operating conditions, this reactor will accumulate several hundred kilograms of metal dust (from materials facing the plasma) which may be radioactive, exhibit acute chemical toxicity or even form, with air and water vapor, a potentially explosive mixture. To answer these safety issues, I have adopted complementary approaches based on experimental and numerical work. First, a dust sampling device was designed and manufactured in order to collect dust deposited on the walls of a fusion reactor. The in situ sampling campaign carried out with this device in the WEST tokamak (CEA/IRFM)made it possible to identify tungsten particles of spherical shape andmicrometric size.With these samples, I was able to perform a parametric in-depth study on adhesion forces using an atomic force microscope (AFM). Distributions of adhesion forces for different particle/surface systems were thus obtained. The results of this study are in very good agreement with an analytical model which makes it possible to describe the adhesion forces according to the size of the particles and the roughness of the surfaces. I continued the study by performing measurements of the electric potential of particles when labeled with tritium using Kelvin Probe Microscopy (KPFM). The sensitivity of this technique allowed me to demonstrate a difference in surface potential between « neutral » steel particles and steel particlesmarked with tritium. The electric charge of these particles could be explained using a self-chargingmodel and Monte Carlo simulations. Finally, resuspension experiments with tungsten particles loaded with tritium were carried out. The results of these experiments are in agreement with a resuspension model in the case where the adhesive force distributions obtained previously by AFM are taken into account. These results, combined with the validation of a particle resuspension model, provide robust data for dust management, safety analysis and definition of radiation protection plans for future nuclear fusion facilities.

Jury

• M^me Emmanuelle Lacaze (CNRS – Sorbonne Université, examinatrice)
• M^me Rosine Coq Germanicus (Normandie Université, examinatrice)
• M. Khaled Hassouni (Université Paris nord, rapporteur)
• M. Alfred Weber (Université de Clausthal, rapporteur)
• M. Olivier Pluchery (Sorbonne Université, directeur de thèse)
• M. Christian Grisolia (CEA, co-directeur)