Inert Matrix Fuels for Plutonium Disposition in PWRs

Inert matrix fuel is an non-fertile oxide fuel consisting of PuO2, either weapon-grade or reactor-grade, diluted in a mixed compound of inert oxides such as stabilized ZrO2, Al2O3, MgO or MgAl2O4, and its primary advantage is the no-production of new plutonium during irradiation, because it does not contain uranium (U-free fuel) whose U-238 isotope is the departure nuclide for breeding Pu-239. This new fuel will have a plutonium relative content comparable to that one used in standard MOX fuel for PWRs. After discharge from reactor and adequate cooling time, the spent fuel is outlooked to be sent, as a HLW, directly to the final disposal in deep geological formations without requiring any further reprocessing treatment (once-through solution). Calculations related to using inert matrix U-free fuel in commercial PWRs, operating in a once-through cycle scheme, show that IMF has a quite high Pu burning capability: >93% of fissile plutonium and 74/85% of total RG-/WG-Pu is burnt at end of fuel life. The calculations evidentiate also that radiotoxicity levels in inert matrix spent fuel, do not appear to increase with respect to standard unreprocessed spent fuel. Moreover the fabrication tests on simulate fuel demonsrate that the nuclear-grade specifications can be met and a very limited solubility under the current fuel reprocessing techniques, coupled to the quality-poor residual Pu in the spent fuel, will make inert matrix fuel a potentially strong anti-proliferation product.