Improved CVD Coatings for NTP Fuel Elements, Phase I

The development of a high quality coating for space nuclear reactor fuel elements could have potential across a variety of nuclear applications. A variety of designs exist for the next generation nuclear power plant, such as the Gas Cooled Fast Reactor (GCFR) and the Very High Temperature Reactor (VHTR). In the case of both of these the final fuel form has not been decided. The triso fuel particle has been suggested for both as well as clad solid fuel pins. Either of these two fuel forms could benefit from an improved fuel coating of this type. The idea of using mixed carbides (U,Zr)C, (U,Nb)C, which would allow for much higher operating temperatures, for both pellets and solid fuel pins has been put forth and both would require a cladding material. Most of these systems will operate above the temperature limit of SiC or would have compatibility issues with the standard C/C/SiC/C (triso) coating developed for pebble type fuel. The case of the VHTR the reactor has the ability to generate hydrogen by splitting water molecules, the presence of hydrogen and oxygen pose serious problems for the triso coating. The development of a high quality coating for space nuclear reactors will be enabling for the development of nuclear thermal propulsion (NTP), in particular if one uses fuel elements based on the Rover/NERVA heritage design or the Pebble Bed design. The higher specific impulses afforded by NTP will provide significantly shorter travel times to the moon and Mars, reducing the time in zero gravity for manned missions and greatly increasing the speed of cargo/supply deliveries and unmanned exploration missions. More »