UO₂グリーンペレットの中心加熱による結晶成長とボイドの挙動

抄録

From the microstructure and the other experimental data obtained from centrally heated UO₂ green pellets, the following conclusions have been obtained.
(1) Observations of the microstructure from the outer to central parts of the pellet indicate that the outer part usually has a sintered microstructure, but in the central part of the pellet the relation between grains and voids becomes very important as follows.
(2) At the higher temperature parts of the pellet, voids gather near the grain boundaries, and form narrow and long voids along the temperature gradient in the pellet. When the edge of the void at higher temperature is heated to a certain temperature, molecules of UO₂ vaporize from this edge and condense at the lower temperature edge of the void. Repetation of this phenomenon, leads to growth of columnar grains with (111) preferred orientation, and long voids mentioned above are transformed in shape to lenticular voids. This phenomenon of the grain boundary void transformation is clearly revealed in the above mentioned transversal microstructures.
(3) Growth is observed at the low temperature side of crack in the pellet, despite prevailing temperature too low to cause the above mentioned phenomenon. This grain growth is assumed to be of the common pattern.