Development of Security and Safety Fuel for Pu-burner HTGR

To develop Pu-burner high temperature gas-cooled reactor (HTGR) attaining very high burn-up around 500 GWd/t, the security and safety fuel (3S-TRISO fuel) is proposed. The 3S-TRISO fuel employs the coated fuel particle with a fuel kernel made of plutonium dioxide (PuO2) and yttria stabilized zirconia (YSZ) as an inert matrix. Especially, a zirconium carbide (ZrC) coating is one of key technologies of the 3S-TRISO, which performs as an oxygen getter to reduce the fuel failure due to internal pressure during the irradiation. R&Ds on ZrC coating directly on the dummy kernel made of YSZ which surrogates PuO2-YSZ have been started in the Japanese fiscal year 2015. As results of ZrC coating tests on YSZ particle by the bromide process developed in Japan Atomic Energy Agency, stoichiometric ZrC coatings with 18 21 μm of thicknesses were obtained with 0.1 kg of particle loading weight. As indicated by a thermochemical analysis on the chemical stability of YSZ against the ZrC bromide process, no deterioration of YSZ exposed by source gases of ZrC bromide process was observed through the characterization by Scanning Transmission Electron Microscope (STEM) observation. Finally, reproducibility of stoichiometric ZrC coating on YSZ particle was demonstrated by the bromide chemical vapor deposition process.