Titanium Carbide Coating for Hafnium Hydride Neutron Control Rods: In Situ X-ray Diffraction Study

Abstract

This article considers the possibility of using a magnetron-deposited coating for the protection of hafnium hydrides at high temperatures as a material for neutron control rods. We describe the role of TiC coating in the high-temperature behavior of hafnium hydrides in a vacuum. A 1 µm thick TiC coating was deposited through magnetron sputtering on the outer surface of disk HfHx samples, and then in situ X-ray diffraction (XRD) measurements of both the uncoated and TiC-coated HfHx samples were performed using synchrotron radiation (at a wavelength of 1.64 Å) during linear heating, the isothermal stage (700 and 900 °C), and cooling to room temperature. Quadrupole mass spectrometry was used to identify the hydrogen release from the uncoated and TiC-coated hafnium hydride samples during their heating. We found the decomposition of the HfH1.7 phase to HfH1.5 and Hf and following hafnium oxidation after the significant decrease in hydrogen flow in the uncoated HfHx samples. The TiC coating can be used as a protective layer for HfHx under certain conditions (up to 700 °C); however, the fast hydrogen release can occur in the case of a coating failure. This study shows the temperature range for the possible application of TiC coatings for the protection of hafnium hydride from hydrogen release.