Factors Affecting the Stability of Matrix Materials for Actinides Transmutation and Conditioning

Abstract

The minimization of the long-term radiotoxicity of high level nuclear waste is an important criterion adopted for the development of advanced fuel cycles for the new generations of nuclear reactors [1, 2, 3]. Pu recycling as fuel, and transmutation of Minor Actinides (MA: Np, Am, and in some concepts also Cm) in reactors and/or MA burners are the steps considered to achieve this goal. U-free compounds are considered as matrices for Pu, MA burning. In some cases, these matrices are envisaged also for the conditioning and immobilization of radionuclides in final disposal concepts. The list of properties of a good inert matrix includes good chemical compatibility with the actinides, easy and economical processes of fabrication and, if required, reprocessing, and good thermo-mechanical performance in-pile, in terms of thermal transport, swelling and high temperature stability. In addition, the material must retain the good properties under the cumulative effect of radiation damage, and fission product accumulation. Since good radiation resistance materials usually exhibit poor thermal transport, in some concepts the actinides are stabilized in a host phase (e.g. zirconia) dispersed in a high thermal conductivity matrix (either ceramic or metallic).