Use of MOX in the disposition of weapons-grade Pu

Five levels of increasing effectiveness are identified in conditioning weapons grade plutonium (WPu) to make it unattractive or unavailable for weapons use. These are: dismantling of weapons delivery systems; dismantling of warheads; converting the metallic WPU to oxides; impeding access to the Pu either by immobilisation and disposal in a high level radioactive waste repository or by burial in a deep borehole; deteriorating the isotopic composition of the Pu. Conversion to MOX fuel seems the most reasonable disposition alternative both for surplus civil grade plutonium (CPu) and the WPU being made available by disarmament, which at 140t represents only 9-12% of the total Pu inventory to be dealt with in the 30-40 years required to eliminate it. In Russia the MOX fuel route only is being considered. MINATOM favours the use of fast neutron reactors but there is pressure from the European Union to consider VVERs as well and suggestions from Canada that some of its CANDU reactors might be used. In the USA, deep boreholes, immobilisation and reactors are still being studied as options. The isotopic composition of WPu, its radioactivity and the fact that the raw material contains 1-2% Ga, will have to be taken into account in the fabrication and design of MOX fuel. Fabrication using CPu is well established in Europe but Russia has rejected the use of any of these facilities for its WPu. Within the reactors option the USA is still considering fabrication in Europe, but problems surround the contamination of the plants with Ga and transatlantic shipment of Pu and MOX. (UK)