PRECIPITATION OF XE AND CS INTO BUBBLES, KINETICS OF BUBBLE MIGRATION AND ALTERNATIVE RELEASE PROCESSES
Very little basic information is so far available on the role of Cs in the formation and migration of ""fission gas bubbles"". Frequently, Cs is assumed to behave in the way the rare gases do. To obtain information on the important question of the behaviour of Cs at high concentrations, ion bombardment techniques were used to prepare specimens with a Cs concentration corresponding to +- 10 at. % b.u. Parallel specimens with Kr or Xe were also prepared. To study possible synergistic effects, double bombardments were made of the type (Kr + Cs) etc. The precursor of xenon, i.e. iodine, was also used. The precipitation of Cs and Kr or Xe was followed by observing the gradual nucleation and growth of bubbles during isochronal annealing treatments. Both UO-2 and an inert matrix (Pt) were used. Additionally, UO-2 single crystals were irradiated at low temperature to a burn-up of +- 0.1 at. % and the above phenomena were again analyzed in the electron microscope. Bubble or void nucleation occurred largely independently of the nature of the implanted species. Cs formed precipitates of predominantly crystallographic shape. Fission product bubbles were observed to migrate only at temperatures above +- 1600 degrees C, but not all bubbles were mobile. The final release occurred quite abruptly and was connected with recrystallization or sweeping processes by extended planar defects clearing the lattice from Cs and rare gases rather than to bubble mobility. The probably relevance of such mechanisms to the overall release from fuel elements is discussed.
Bibliographic Reference: SPECIALIST WORKSHOP ON FISSION GAS BEHAVIOUR IN SAFETY EXPERIMENTS, CADARACHE/F, OCT. 5-7, 1983
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Record Number: 1989122066200 / Last updated on: 1987-01-01
Available languages: en