Study of PVC behavior under the combined action of alpha particles and temperature: gas emission in the context of radioactive waste transportation

Polymers are present in numerous technological radioactive wastes. Among those, Polyvinylchloride (PVC) is the most common.  In the course of its usage, it is contaminated with alpha-emitting particles, leading to radiolysis, resulting in the formation of macromolecular defects and gas emission. The main gases emitted from PVC under irradiation are H₂ and HCl, each of which presents a specific risk in presence of molecular oxygen: flammability and explosion for H₂ and corrosion (in the presence of H₂O) for HCl. As corrosion also initiates H₂ emission, the mitigation of the risk resulting from H₂ is the major challenge in the storage and transportation of nuclear wastes.

In the framework of nuclear waste transportation, polymers can be subjected to the combined effect of radiolysis and temperature in presence of molecular oxygen. Numerous studies exist on the behavior of PVC exposed to electron beams or gamma rays at room temperature but very few exist on the influence of the irradiation temperature in these conditions of low LET. In presence of alpha particles the studies are sparser; even at room temperature.

The aim of the present thesis is thus to study the behavior of PVC under a particle irradiations at temperatures varying from room temperature to 180°C with the goal of understanding the impact of temperature on defects creation and gas emission mechanisms. The objectives are to characterize and quantify outgassing and macromolecular defects first at room temperature under various oxygen pressures and then at different temperatures under the same oxygen conditions. Besides, the evolution of the same defects will be studied under the sole thermolysis conditions with the aim of decoupling the radiolysis from the thermolysis and extracting a potential synergetic effect.

The effect of alpha particles will be simulated using finely selected swift heavy ion beams at GANIL. Some low LET irradiations (X-rays and gamma-rays) will also be performed to assess the specific effect of the high LET induced by ions on the mechanisms under study. These irradiations will be performed using a specific device to be developed during the thesis. Defects will be analyzed on-line using FTIR, mass spectroscopy and µ-GC and off-line using DSC, HPLC (for extracted solutions), and GC-MS.

At the completion of this thesis work, the PhD will have valuable expertise in the study of material under ionizing radiation, in oxidation ageing and radiolysis, in analytical chemistry and in the physics of ion/mater interactions. These skills are applicable in domains other than radiolysis. More broadly, they will have acquired a solid experience in managing a multidisciplinary project.

Le CIMAP (Centre de recherche sur les ions, les matériaux et la photonique) est une unité mixte (UMR 6252) regroupant le CEA, le CNRS, l’ENSICAEN et l’université de Caen Normandie. Son activité s’organise autour de trois missions : recherche, enseignement et accueil des recherches interdisciplinaires auprès des faisceaux d’ions du GANIL (Grand Accélérateur National d'Ions Lourds). Les activités de recherche s’intéressent aux aspects théoriques, expérimentaux et appliqués portant sur : l’interaction ion-matière et la relaxation des matériaux excités, l’étude des défauts dans les matériaux, les matériaux pour les lasers, la photonique et l’électronique.

The applicants should hold-or be preparing- a Master II in chemistry, physical chemistry or material science and should be interested in experimental research. Engineers and engineering school students can benefit from a Master II exemption.