[en] The increasing availability of fissile material and the worldwide perception of the need to reduce or control such material make a new approach towards nuclear reactors necessary. The Nuclear Fission Division at ENEA is presently interested in evaluating various options for the burning of excess plutonium, among which the LWR reactors using rock-like inert matrix fuel in a once-through cycle and fast reactors with recycling. This paper deals with the latter option. A fast system, rich in neutrons, can produce plutonium by breeding, or it can burn it (together with Minor Actinides) with a high degree of effectiveness: this flexibility makes the fast system worth considering. In the framework of a co-operation project between GE-USA and ENEA, the PRISM MOD D oxide-fuelled reactor (small size, 840 MW) was studied as a burner. A complete set of studies was carried out covering several fields: neutronics, thermohydraulics, dynamics and safety. A negative void coefficient was achieved thanks to a particular arrangement of the fuel subassemblies (leaky core) and to the enrichment distribution. The central zone, loaded with shielding subassemblies, accounts for a negative void coefficient even in the inner zone. Moreover, this zone could become a suitable place for burning long-lived fission products. As a burner, using a standard fuel, the expected performance is a consumption of about 60-70 kg Pu/TWhe. ULOF and TOP analysis show a begin transient evolution. Only half of the GEMs are sufficient to close the ULOF transient; the reactor power reaches its maximum at 1.35 of the nominal figure during a TOP accident. A method of detecting a failure in a subassembly and identifying the subassembly concerned was developed. It was demonstrated that it is possible to create a sufficient number of tags for them to be recognised as different by the detector system, by using 'cocktails' of only four tag gases. The total gas required to overcome the uncertainties is less than 15 ncm³ of gas/pin. This method assumes that the detector system is unable to measure the absolute quantities, but only the mutual rations. By processing the results of the detector system with a simple code, the effectiveness of the method can be significantly increased. Moreover, experimental measures can be used to reduce the required quantity of gas. (author)