Inert matrix fuels to reduce the radiotoxicity of nuclear waste

Inert matrix fuels are U-free fuels to effectively burn, or transmute, surplus and ex-military 239Pu and 235U, the 'minor' actinides Am, Np and Cm, and possibly long-lived fission products such as 129I and 135Cs, thus reducing significantly the radiotoxicity of nuclear waste. The three alternatives of cercers, i.e. a ceramic actinide compound in an inert, i.e. no actinide producing matrix, such as AmO2 in Mg O, of cermets, i.e. a ceramic actinide compound in a metal matrix, such as AmO2 in Mo or Zr, and solid solutions as ceramics, e.g. (Ce,Am)O2, are discussed. The criteria for selecting inert matrices are summarized, the effects of radiation damage are reviewed and optimized, innovative concepts are described, such as 'hybrid' fuels of a dispersion of an actinide host phase, e.g. (Zr,Am)O2 in an inert matrix such as spinel MgAl2O4. With such optimized fuels, radiation damage effects can be minimized and the thermal behavior can be optimized. (author)