FFTF driver fuel experience

The Fast Flux Test Facility is a 400 MWt, sodium-cooled, loop-type reactor located in Richland, Washington. by the end of Cycle 3, after 336 equivalent full power days the driver fuel achieved the initial design burnup of 80 MWd/kg with flawless performance. Because of the excellent performance of the driver fuel assemblies up to their design lifetime is was decided to extend the irradiation of several assemblies to establish the actual lifetime limit. As a result of the continuing irradiation it was confirmed that the lifetime of the driver fuel assemblies could be extended to a peak duct fluence of about 17.5 x 10/sup 22/ n/cm/sup 2/ (E > 0.1 MeV). The demonstration that the lifetime of the driver fuel assembly was duct fluence limited rather than fuel pin burnup limited has been further confirmed by the fact that over a third of the assemblies irradiated in FFTF since the initial power demonstration have exceeded 80 MWd/kgM. As a result of its high reliability the driver fuel system lifetime is now about 100 MWd/kgM in the inner enrichment zone corresponding to the fast fluence limit for the duct of 17.5 x 10/sup 22/ n/cm/sup 2/.