Characterization of radiolytic mechanisms in tritiated water–zeolite systems under storage conditions

The operation of the tritium facilities at Valduc generates low-activity tritiated liquid effluents, which are stored in an adsorbed form on 4A zeolite for operational reasons. Understanding the mechanisms of self-radiolysis of this confined water is essential for optimizing storage conditions.
Several PhD projects have already investigated these mechanisms by combining experiments and modelling. Early work showed that below 13% hydration, the radiolytic gases H2 and O2 can recombine within the zeolite. Subsequent studies, based on DFT calculations and molecular dynamics, identified the adsorption sites and the mobility of the gases. They revealed a hydration threshold (13–15%) above which gas diffusion becomes very low, consistent with the experimentally observed cessation of recombination. However, these simulations rely on idealized models.
The new proposed PhD aims to shift the project back toward experimental work in order to better reflect real storage conditions. It will begin with a detailed characterization of the zeolite used industrially. Water–zeolite reservoirs will then be irradiated to simulate the effect of tritium, and analyzed by NMR and possibly by Electron Spin Resonance (ESR) to detect reactive species. The experimental results may feed into a macroscopic model (Kinetic Monte Carlo, KMC), also developed previously, to predict the evolution of the system and identify possible optimizations for storage. The work will be carried out mainly at the NIMBE laboratory (CEA-CNRS), with simulation collaboration in Besançon and regular exchanges with CEA Valduc.