Estimation of Hydrogen Redistribution in Zirconium Hydride under Temperature Gradient

Abstract

To evaluate irradiation behavior of δ-ZrH_x+U fuel, thermal migration of hydrogen under temperature gradient has been estimated according to traditional diffusion theory. Hydrogen profiles at steady state and diffusion kinetics in single-phase δ-ZrH_x have been calculated for a cylinder specimen. When a temperature gradient is imposed on the initial uniform ZrH_1.6 hydride, considerable thermal migration from the higher temperature center region to the pellet surface can be expected. Larger temperature gradient and lower temperature will cause greater inclination of the hydrogen distribution. The hydrogen transportation process in single-phase δ-ZrH_x as a function of time was simulated by a finite difference method. In the case of two-phase δ-ZrH_x+45 wt%U, the uranium phase tends to slow down the thermal migration rate of hydrogen by about 50% compared with that in single phase δ-ZrH_x though it may have little influence on the final hydrogen distribution in the δ-ZrH_x matrix. For the cylinder specimen under the temperature conditions of interest, the steady state would be reached at an early stage of the typical irradiation cycle. Finally, the engineering impact due to the redistribution was discussed.

KEYWORDS:

• hydrogen
• zirconium
• hydrides
• zirconium alloys
• diffusion
• kinetics
• temperature gradients
• radiation effects
• temperature dependence