High temperature zirconium carbide coatings for use in particle bed reactors

The Particle Bed Reactor is composed of one-half millimeter in diameter nuclear fuel particles held in a fixed bed configuration by frits and cooled by a gas flowing through the bed and frits. The operating temperature of the reactor is in the 1500 to 3000/degree/K range depending upon its projected use. The gas coolant may be an inert gas for closed cycle systems, hydrogen, or decomposed ammonia for open cycle propulsion systems. The high temperature approx.2500/degree/K hydrogen system requires a coating on the frits and fuel particles that will not react with hydrogen. Zirconium carbide particles (1/2 mm) were tested at 2000/degree/K in flowing hydrogen gas for twelve hours with little or no reaction (<0.1% weight loss). They also showed no visible surface change under the microscope. Test fuel is being coated with zirconium carbide by the zirconium chloride vapor reaction process. Test frits made by the carbon fiber-carbon composite method have been made and will be coated with zirconium carbide and incorporated in the full-sized fuel element. 5 refs., 12 figs.