THE GAS DEPOSITION OF PYROLYTIC GRAPHITE AND NIOBIUM CARBIDE PROTECTIVE COATINGS ON GRAPHITE FUEL ELEMENTS OF KIWI-A PRIME AND KIWI-A3

摘要

This report describes the methods and apparatus used to coat Kiwi-A Prime and Kiwi-A3 graphite fuel elements with a protective coating of NbC. A new coating method was employed for this purpose. It consisted of the high-temperature reaction of a gaseous mixture of niobium pentachloride, hydrogen, and hydrogen chloride with the graphite of the fuel element to form a NbC coating on the element. Since this gas mixture also reacts:with the uranium dicarbide in the fuel element to form volatile uranium tetra chloride ga3, an initial impervious pyrolytic graphite coating was deposited on the elements. Both of these coating processes are described in detail, as well as the procedures for inspection and evaluation of the coats.