[en] The report describes the reprocessing of 2.7 kg of highly irradiated UO₂-PuO₂ fast breeder fuel in the experimental facility MILLI of the Institut fuer Heisse Chemie (IHCH). The fuel contained 15% PuO₂, the initial uranium enrichment was 60% ²³⁵U, and the cladding material was stainless steel. The fuel had been prepared in England by coprecipitation of UO₂ and PuO₂ and calcination, and had been irradiated in the Dounreay Fast Reactor to a burn-up level of 61,000 MWd/t. The cooling time was ca. 7 years. The material dissolved essentially completely in boiling nitric acid at HNO₃ concentrations %T >= 8 moles/l. Insoluble residues amounted to < 0.7%, and were analysed for U, Pu and fission products; less than 0.08% of the total fissile material remained in the insolubles. The separation of U and Pu from fission products was carried out by a modified Purex process designed at IHCH Karlsruhe for the suppression of crud formation; this process is characterized by a high HNO₃ concentration (3 to 3.5 moles HNO₃/l) and a high organic loading (ca. 110 g U + Pu/l) in the first extraction cycle. A smooth and undisturbed operation was observed over the whole campaign of 30 hours duration, thereby demonstrating for the first time the effectiveness of this flowsheet with a mixer-settler facility on a high-activity level. The U/Pu separation was carried out in the third extraction cycle with an electrolytic multi-stage mixer-settler (EMMA), using the in-line electrolytic process developed by IHCH Karlsruhe, thereby demonstrating for the first time the effectiveness of this process with high-burn-up fuel. Losses of U and Pu over the whole reprocessing campaign were low. (orig.)