[en] The irradiation of a fuel pin in a nuclear power plant drastically modifies the structure of the starting materials so that in some cases failures of the clad can occur. On the basis of the knowledge gained in the U-Pu MOX system, calculations have been performed with the CODACT and TPROF computing codes in order to investigate the behaviour of fuel pins and target elements containing oxides of Np-Am-Cm for homogeneous and heterogeneous recycling in LWR and FBR. The irradiation conditions must assure that: the specific power rating (W/cm) does not exceed the value accepted for a normal fuel; the central temperature is compatible with the melting point of the materials or with possible eutectic temperature; thermodynamic conditions leading to dangerous fuel-clad interaction are avoided. The calculations show that this hold true for homogeneous pellet of current fuels containing up to 1% actinide oxides (Am, Cm, Np), while the heterogeneous concept for FBR request modification of the pin geometry and of the fuel composition and implies supplementary costs and difficulty for the fabrication. Dense pellets of actinide oxides blended with the inert diluent MgO seem to be the most promising solution. The critical evaluations of the parameters influencing the central temperatures and the radial oxygen profiles are made on a purely theoretical approach because of the lack of experimental data concerning the solid phases containing actinide oxide