Abstract
WB2 and TaB2 dispersives in UO2 were heated in flowing steam and in static high-pressurized steam, and the reaction between steam and borides was studied by means of the X-ray diffraction method and optical microscopy.
The main results obtained are as follows:
(1) Powder compacted specimens of UO2–WB2 and UO2–TaB2 reacted with the flowing steam at 600°C. WO2 and H3BO3 were formed for UO2–WB2, and Ta2O5 and H3BO3 for UO2–TaB2. It was considered that the boron element migrated out of specimens in the form of a gaseous compoud. There were no reactions between UO2 and borides in steam.
(2) In the sintered pellet specimen of UO2–WB2, there were no appreciable changes in the shape and location of the WB2 particles even after heating at 600°C, while in the UO2–TaB2 specimen a new phase, which was considered as Ta2O5, appeared in the annulus region surrouding each TaB2 particle after heating at 600°C, although no appreciable migration of TaB2 particles was observed.
(3) The effect of pressurizing of steam on the behaviors of UO2–WB2 and UO2–TaB2 was not recognized in the temperature range below 400°C.
