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Current investigations on tritiated dust and its impact on tokamak safety

par Caroline CHAMPENOIS - publié le

vendredi 28 juin 2019 à 14h30 en salle du conseil de PIIM service 322.

Current investigations on tritiated dust and its impact on tokamak safety
Christian Grisolia
Institut de Recherche sur la Fusion Magnétique (IRFM) CEA Cadarache

During the operation of tokamaks and due to plasma/wall interaction, particles (called dusts in the fusion community) are created. They have variable sizes ranging from nanometers to tens of microns. The properties of these particles, such as their ability to be covered by an insulating oxide layer or their surface topology that affects their tritium inventory, are essential to describe their behavior in the tokamak. After having recalled the different processes of creation of particles during the operation of a tokamak, we will endeavor to describe the physicochemical properties specific to tritiated tungsten particles. We will recall their inventory in tritium, inventory which varies according to their specific surface. We will then specify how these tritiated particles acquire, over time, a positive electric charge, a load that we will determine. These electrostatic properties modify the adhesion of dust on the surfaces on which they are deposited. We will argue that in the case of a single particle, adhesion is enhanced. However, if the tritiated particle is part of an aggregate (a pile of particles), the adhesion remains unknown but should be very small. Due to the limited free path of the β emission in the material, the tritium inventory transported by the aerosol created during their suspension in the air during a "Lost Of Vacuum Accident" for example cannot be measured in real time by conventional measurement methods. A new measurement strategy is necessary for measurements at the workplace, for example, or during release into the environment. We will also present the results of toxicity studies on the in vitro exposure of lung cells to 100 nm untritiated / tritiated tungsten particles. Finally, after the collection of these powders by aspiration, it is necessary to avoid their dispersion in the environment. We will specify the different technical solutions that we will envisage.

contact : Jean-Marc Layet


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