Post-accident heat removal (PAHR) experiments are being conducted in BR2 as part of the fast reactor safety program of the Commission of the European Communities. In the first experiment a mixture of UO² particles in a crucible with sodium has been irradiated in the central channel of BR2 at a temperature of about 1500°. Two similar experiments will be performed in the future at higher temperatures.

Neutron and gamma calculations (one- and two-dimensional) contributed to the optimization of the irradiation device and determined the heating rate distributions and level. The latter is compared with the results of an analysis of the data collected during the irradiation. As quality control of the particle bed, a neutron transmission measurement with a beam issuing from the BR1 reactor allowed us, before the irradiation, to scan the bed in order to determine its porosity variation.