Abstract
Gamma scanning and electron probe microanalysis results are reported for LWR fuels transient-tested in the first Risø Fission Gas Project. The fuels, which had been prepared from powders supplied by Risø National Laboratory (R fuel) and the UKAEA (U fuel), had been transient-tested to powers in the range 30.1 to 44.4 kW m −1 at a burn-up between 3.6 and 4.5 at%. It was found that considerable radial redistribution of Ba had occurred during the transient tests. Evaporation-condensation of BaO had led to the formation of BaSiO 3in pores and cracks at intermediate radial positions. As a result of thermal diffusion up the temperature gradient, Ba had also accumulated in the centre of the fuel. Although radial redistribution of barium occurred in both the R and U fuels, only the R fuel released Ba to the rod free volume. In rods that had been transient-tested to powers greater than 41 kW m −1, accumulations of 140Ba were found at the pellet interfaces. The release of Ba is ascribed to the evaporation of BaO in the central region of the fuel at temperatures above 2000° C. Indications were found that the U fuel operated at a lower temperature than the R fuel. Therefore, it is concluded that the U fuel never reached 2000° C, even at the highest terminal power of 44.4 kW m −1.
Published Version
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