In France, 35 nations are collaborating to build the world's largest tokamak, a magnetic fusion device that has been designed to prove the feasibility of fusion as a large-scale and carbon-free source of energy based on the same principle that powers our sun and stars. The commissioning of the ITER experimental fusion facility will produce low- or intermediate-level radioactive waste with significant amounts of tritium, a radioactive isotope of hydrogen. To be acceptable in a repository, tritiated waste packages must exhibit a very low outgassing rate, which is difficult to achieve, unless the waste incorporation rate is drastically reduced or the waste is previously de-tritiated.The interest of dispersing oxide getters of the ?-MnO2 / Ag2CO3 type within the cementitious conditioning matrix to mitigate the gas release has been evidenced in a recent work carried out at CEA. Nevertheless, the experiments have been carried out over a limited period of time (a few months) with materials cured under endogenous conditions. The question then arises of the evolution of the trapping properties at later age for a material interacting with its environment. In a first part of the study, the trapping properties of dihydrogen, used as a surrogate of tritium, will be investigated as a function of the water saturation degree of the material. Then, the focus will be placed on the chemical evolution of the getter in a cementitious environment, and on its consequences for dihydrogen trapping. A large panel of experimental techniques will be used to characterize solids (XRD, TGA, SEM, TEM, XRF, XPS), solutions (ICP-AES,ICP-MS, ionic chromatography) and gases (gas chromatography). In addition, models (reactive transport, surface complexation) will be built to analyze the experimental data.
This multidisciplinary project is intended for a PhD student in materials chemistry interested by energy issues, and wishing to open up new opportunities for the conditioning of radioactive waste. It will build upon the expertise of three laboratories at CEA: the Cements and Bitumen for Waste Conditioning Laboratory (CEA) for materials elaboration and characterization, the Expertise and Destructive Characterizations Laboratory (CEA) for gas diffusion experiments, and the Radionuclides migration Measurement and Modelling Laboratory for modelling the experimental data.