[en] Summary: A major task within the US/FRG Spent Fuel Treatment Development Subprogram (Ref. 1) is the conceptual design of a Joint US/FRG Cold Prototype Head-End Facility (JPHF). Since 1979, the conceptual design activity has been supported by an experimental program called the Joint Fuel Processing Demonstrations (JFPD). The primary objectives of the JFPD activities have been to verify design assumptions, answer open questions and provide necessary baseline operating data for formulation of JPHF system and component requirements. Extensive experimental results are available concerning the burning of American reference hexagonal prismatic fuel elements (Ref. 2). In order to obtain congruent data for the FRG reference fuels, two JFPD tests have been completed using 10000 HEU mixed oxide (U, Th)O₂ spherical fuel elements (Ref. 3 and 4). The tests described herein, using both HEU-MO and LEU-UO₂ fuel elements represent a continuation of the JFPD cooperative effort. The previous experiments in 1980 demonstrated the basic suit ability of fluidized bed burning for removal of the fuel element matrix graphite. However, operational difficulties were encountered when the FRG fuels exhibited an extremely high fines generation and elutriation rate, causing a rapid build up of fines in the existing above bed fines recycle system. Because of these difficulties, additional JFPD activities were scheduled for 1981, including the following objectives: - Investigate the results of below bed fines recycle with regard to increased fines burn rate, reduced fines elutriation and improved burner operation compared with the results in 1980 with HEU-MO-FE (Special Tests). - Test the modified primary burner system with FRG LEU-UO₂- TRISO spherical fuel elements in so called LEU-Tests (Low Enriched Uranium).