In the fabrication of fuel containing transuranium (TRU) elements, flow sheets and techniques that allow a shielded and/or remote fabrication will probably need to be applied. One approach, which has been demonstrated on the laboratory and semiprototype scale, is the wet fabrication route of coprecipitation of the matrix element uranium mixed with plutonium to form either dense spherical particles or to produce hybrid pellets made from pressed gel microspheres. The ceramic material produced holds the TRU elements homogeneously distributed in the matrix. In conjunction with the Département d’Études des Combustibles of the French Commissariat à I’Énergie Atomique in Cadarache, France, the Paul Scherrer Institut in Switzerland is further developing a mixed nitride ceramic and mixed oxide with high concentrations (up to 50%) of plutonium with the aim of a joint irradiation test of TRU elements in the French Phénix reactor.