Safe disposal of surplus plutonium

About 150 tons of weapons grade and weapons usable plutonium (metal, oxide, and in residues) have been declared surplus in the USA and Russia. Both co untries plan to convert the metal and oxide into mixed oxide fuel for nucle ar power reactors. Russia has not yet decided what to do with the residues. The US will convert residues into a ceramic, which will then be over-poure d with highly radioactive borosilicate glass. The radioactive glass is mean t to provide a deterrent to recovery of plutonium, as required by a US stan dard. Here we show a waste form for plutonium residues, zirconia/boron carb ide (ZrO2/B4C), with an unprecedented combination of properties: a single, radiation-resistant, and chemically durable phase contains the residues; bi llion-year-old natural analogs are available; and criticality safety is giv en under all conceivable disposal conditions. ZrO2/B4C can be disposed of d irectly, without further processing, making it attractive to all countries facing the task of plutonium disposal. The US standard for protection again st recovery can be met by disposal of the waste form together with used rea ctor fuel. (C) 2001 Elsevier Science B.V. All rights reserved.