On the correlation between mechanical and TEM studies of the aging of palladium during tritium storage

Tritium has considerable technological applications in nuclear industry. Since it is a radioactive element, its storage is often considered in the form of tritides which ensure the required safety. However, the decay of tritium into 3He alters the tritide properties during aging. With the aim of understanding the aging mechanisms of palladium tritide, a macroscale approach coupled with a microscopic study was performed on palladium aged up to eight months after tritium loading. The macroscale investigation based on the vibration of microcantilevers allowed the mechanical response of the material to be followed during its aging. The microscopic study was performed by Transmission Electron Microscope (TEM) and led to the observation of 3He nanometric bubbles within the material at different ages. The Young's modulus was found to grow mainly during the first weeks of aging. The bubble density was found to remain almost constant after the first month while their diameter grew very slightly after further aging. As a result, both methods showed the importance of the phenomena occurring during the first month of aging in the case of palladium tritide.