| Popis: |
A continuing chanllenge to thermionic fuel elements is degradation of the sheath insulator in the high temperature and high neutron flux environment. Also, the present alumina insulator requires a barrier coating to isolate it from the alkali metals. The recent successes in applying polycrystalline films to metals led to the consideration of diamond as the ideal sheath insulator. Diamond possesses several of the intrinsic characteristics demanded of a sheath insulator, e.g., the highest combination of electrical resistivity and thermal conductivity at room temperature, compatibility to alkali metals, and high neutron radiation tolerance. However, a number of durability issues must be resolved before the practicality of diamond insulators can be assessed in prototype thermionic diodes. Also, since the fabrication techniques for thin diamond films are undergoing extraordinary advancement, the structural integrity and reproduceability are yet to be addressed in a systematic manner. Recent results increase the understanding of diamond as a sheath insulator. The paper quantifies the potential advantage, identifies the issues to be resolved, and summarizes the progress in resolving the issues. |
