Empirical and physics-based mathematical models of uranium hydride decomposition kinetics with quantified uncertainty

Abstract

Metal hydride particle beds have recently become a major technique for hydrogen storage. In order to extract hydrogen from such beds, it is crucial to understand the decomposition kinetics of the metal hydride. We are interested in obtaining a better knowledge of the uranium hydride decomposition kinetics. We first developed an empirical model fit to measurements compiled from different experimental studies in the literature and quantified the uncertainty resulting from the scattered data. We found that the decomposition time range predicted by the obtained kinetics is in a good agreement with published experimental results. Secondly, we developed a physics-based mathematical model to simulate the rate of hydrogen diffusion in a spherical hydride particle during the decomposition. We used this model to evaluate the kinetics for temperatures ranging from 300K to 1000K while propagating parametric uncertainty. We have compared the kinetics parameters derived from the empirical and physics-based models and found that the uncertainty in the kinetics predicted by the physics-based model covers the scattered experimental data. Finally, we used the predicted kinetics parameters to simulate the effects of boundary resistances and powder morphological changes during decomposition in a continuum level model. We found that the phase change within the bed occurring during the decomposition accelerates the hydrogen flow by increasing the bed permeability, while the pressure buildup and the gap forming at the wall significantly impede the hydrogen extraction. We also found that there is significant uncertainty in the bed decomposition time at the lower range of the kinetics.