Coating development on graphite-based composite fuel for nuclear thermal propulsion

ORNL is currently recapturing graphite-based fuel forms for Nuclear Thermal Propulsion (NTP). Previous work at ORNL focused on reviewing historic fuel technology developed during the ROVER/NERVA programs and performing coating development at the lab scale. The current effort focuses on transitioning the coating work from the lab scale to an intermediate length, and coating an element with a more prototypic geometry to include a hexagonal cross section and multiple internal channels. A new vertical multi-zone furnace capable of coating 16“ length elements was installed and the ability to deposit a ZrC coating along the full length of the element demonstrated. A chemical vapor deposition (CVD) process was used to apply a ZrC coating where zirconium metal was chlorinated in-situ forming ZrCl₄ as the Zr precursor and CH₄ was used for the carbon source. The coating and additional diluent gases were directed through the internal channels using custom fixtures. While processing conditions were not fully optimized, good progress was made in coating development. Between the information gained and new capabilities installed, an excellent foundation for further fuel development and eventual qualification has been put into place.