[en] The Paper provides a general description of the BIZET experiments carried out at Zebra under collaboration between the DeBeNe and UK Fast Reactor Projects. This programme included a large assembly representing the essential features of a conventional power reactor and also two cores incorporating internal breeder regions typifying current heterogeneous designs. Emphasis throughout was on validating predictions of reaction-rate distributions, control rod performance, and sodium-voiding reactivity. The scope of these measurements is outlined. A brief account is given of the data and methods being applied to the analysis of results. Conclusions drawn so far from the experiments and their evaluation are summarised. (author)