Release of volatile fission products from ThO(2) with a simulated burnup of 4 at%
One of the possibilities for improving the economics of water-reactor operation is by extending the fuel burnup, which leads to improved fuel utilisation and reduced spent-fuel volumes. At extended burnups, there is growing evidence that the fission-gas release increases more than would be expected from low burnup extrapolation, or from codes developed for low burnup. The paper describes a program designed to examine whether intragranular mobility of fission products increases due to high burnup, without any temperature increase. The program involved fabricating simulated high burnup fuels, UO(2) or ThO(2), with non-active fission products added, and ion-beam implanting a radioactive fission gas or volatile fission product into a thin surface layer. The release of this gas was then monitored for various annealing temperatures and times. The results show clearly that the intragranular mobility is not shifted to lower temperatures in 4 at% ThO(2)-based Simfuel as compared with reactor-grade ThO(2). The conclusion is that the observed increased gas releases, if occurring at constant O/M ratio of the fuel, are more likely to be due to increased fuel temperatures than to increased gas diffusion coefficients.
Bibliographic Reference: Article: Journal of Nuclear Materials, Vol. 182 (1991) pp. 261-264
Record Number: 199111167 / Last updated on: 1994-12-02
Original language: en
Available languages: en