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A series of scanning electron micrographs trace the development of gas bubbles on the grain faces in a transient tested BWR fuel. The observations indicate that gas bubbles nucleate on metallic precipitate particles and that bubble migration is prevented by the precipitates. X-ray fluorescence and electron probe microanalysis results show an accumulation of Xe on the grain boundaries at intermediate radial positions and high "in grain" retention in the centre of the fuel. These findings are ascribed to high compressive forces in the fuel during the transient and an increase in the rate of thermal resolution with temperature. It is concluded that under transient conditions the magnitude of the local mechanical restraint and the existence of macroscopic pressure gradients are important in determining the behaviour of grain face bubbles. In a high pressure field both the bubbles and precipitates grow by Ostwald ripening and little bubble interlinkage occurs. In a non-uniform pressure field bubble interlinkage can take place in areas where the restraint pressure is low and this leads to the formation of escape tunnels at the grain edges. Intergranular cracks which form at the end of the transient when the mechanical restraint pressure is removed also provide escape routes for fission gas.

Additional information

Authors: WALKER C T, JRC Karlsruhe Estab. (DE);KNAPPIK P, JRC Karlsruhe Estab. (DE);MOGENSEN M, Riso National Lab., Roskilde (DK)
Bibliographic Reference: Article: Journal of Nuclear Materials, Vol. 160 (1988), pp. 10-23
Record Number: 198910194 / Last updated on: 1994-12-01
Original language: en
Available languages: en
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