Samuel Peillon will defend his thesis
on Monday 26th October 2020 at 2:00 p.m.
at Sorbonne University Jussieu Campus, Charpak amphitheater
4 place Jussieu
75005 Paris
Jury
Mrs. Emmanuelle Lacaze, Director of Research, CNRS - Sorbonne University, President
Mr. Alfred Weber, Professor, University of Clausthal, Reporter
Mr. Khaled Hassouni, Professor, University of Paris 13, Rapporteur
Ms. Rosine Coq Germanicus, Senior Lecturer, University of Caen, Examiner
Mr. Olivier Pluchery, Professor, Sorbonne University, Director
Mr. Christian Grisolia, Director of Research, CEA, Co-Director
Mr. François Gensdarmes, Research Engineer, IRSN, invited member
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 and micrometric size. With these samples, I was able to perform an
in-depth study 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 charge 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 particles marked with tritium.
The electric charge of these particles could be explained using a self-charging
model 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.
The results of these experiments, 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.