Behavior of a Single UO2 Sphere, Irradiated at Approximately 1900 K in the High Flux Reactor (HFR) at Petten (The Netherlands)

摘要

A UO2 sphere, with an as-fabricated diameter of 1.15 mm, an enrichment of 20% U-235 in U, and a density of 96% to 100% TD, was irradiated during 544 hr in a compacted bed of Al2O3 granules in an aluminum capsule placed in the D-8 core position of a fission reactor. Unexpected fission product release from a similarly irradiated sphere suggested that the achieved maximum temperature was beyond the 1100 K specified maximum. Axial gamma scanning of the capsule and microscopy of a cross section of the UO2 sphere indicate a maximum irradiation temperature of 1930 K. Evaluation of the measured fission products releases in relation to the calculated release contributions from fission product chain members emphasizes the release governing role of the volatile precursors of a by itself nonvolatile, radioactive, end member of a fission product chain.