EPMA of ground U(Mo) fuel with and without Si added to the matrix, irradiated to high burnup

In the framework of the IRIS-TUM irradiation program, several full size, flat dispersion fuel plates containing ground U(Mo) fuel kernels in an aluminum matrix, with and without addition of silicon (2 w%), have been irradiated in the OSIRIS reactor [1]. Microstructural analyses (optical and scanning electron microscopy [2]) on samples from these plates, showed that the irradiation of ground fuel dispersed in an Al-2.1wt%Si matrix to a local maximum burn-up of 88 % 235U LEU equivalent (5.9×1021 f/cm3 U(Mo)), has resulted in a considerable, but yet not break-away swelling of the fuel plate. Comparison to the fuel plate with no Si added up to a burn-up of 66.5 % 235U LEU equivalent (4.4×1021 f/cm3 U(Mo)), again shows the (moderate) positive effect of adding Si, in this case mainly to delay the growth of the U(Mo)-Al-Si interaction layer. Electron probe micro-analyses, provide additional information on the role of Si and the fission gas behavior in ground fuel.