Optimisation of inert matrix fuel concepts for americium transmutation

Concepts of inert-matrix fuels for americium transmutation are discussed. It is demonstrated that a 'hybrid' fuel design, consisting in a dispersion of an americium-bearing phase in an inert matrix, is desirable. More than a solid-solution is preferred in order to localise within a small volume the damage in the matrix due to fission fragments. Such a dispersion is composed of spherical inclusions (between 50 and 300 mu m) of an americium host phase in a dense inert matrix. For an oxide fuel, we recommend the solid solution (Zr,Am)O-2, possibly stabilised by yttrium as the host phase. For a nitride fuel, (Zr,Am)N is proposed. MgO and MgAl2O4 (oxide fuel), as well as TiN and ZrN (nitride fuel) are the most likely candidates for the inert matrix. Recommendations are also given for the research required to optimise the concept. (C) 1999 Elsevier Science B.V. All rights reserved.