Preparation of UO₂ single crystal by induction heating

A UO₂ single crystal 10 mm in diameter and 30 mm long was prepared by means of the floating zone technique. In an atmosphere of 5 atm. nitrogen, a sintered UO₂ rod, 17 mm in diameter and 150 mm long of 97% theoretical density, was heated by high frequency induction in a graphite pipe. The electronic conductivity of UO₂ increased with rising temperature. When the surface temperature of the pipe attained 1,100℃, the pipe was removed and the rod was heated directly by induction. The UO₂ rod was heated at a rate of 500℃/hr, until the surface temperature became 1,850℃ (power supply 18 kW). At this temperature, about 70% of the cross section of the rod been melted, and the nonmelted outer portion acted as crucible. Then the rod was rotated at a speed of 100 r.p.m. and at the same time raised at a speed of 5 mm/hr. After it reached a predetermined height, the rod was again lowered at the same speed to its original position. This double pass generated a single crystal in the central portion. Back reflection Laue photographs taken from different points of the specimen showed that the <111> direction was inclined at about 10° to the axis of the rod. No etch pits were found in the single crystal area. The result of spectroscopic analysis revealed that certain kinds of impurities were concentrated in the lower part. (author)