[en] Development of manufacturing processes and irradiation test results on different types of spherical fuel elements has led to the quasi-isostatically moulded fuel element with homogeneous coupling of fuel zone and fuel-free shell. This fuel element represents the reference design for the first core of the THTR-300. Broad irradiation experience of these moulded fuel elements has been obtained from: high flux rig tests in the Studsvik R2, permitting a quick feed-back of results to fuel element development, prolonged irradiation experiments in the Dragon reactor, the application of a great number of these elements to the AVR reactor, combined with regular post-irradiation examinations, special tests in the Julich DIDO (FRJ-2), normally aiming at fission product release investigations under exceptional conditions. The results of this development and irradiation programme demonstrate the extraordinarily good behaviour of this type of fuel element, even far beyond the THTR target values for burnup and fast fluence, with reference to dimensional and mechanical stability, as well as to the integrity of matrix and coated fuel particles, including fission product retention. The suitability of this approved type of element for the first core of the THTR has been established, but the performance limits are still unknown. (author)