Criticality prevention devices and methods in nuclear fuel production

Containment enclosure for processing material containing civilian or military origin plutonium in the form of plutonium oxide, carbide and/or nitride, and possibly other actinides such as americium, neptunium, or curium, said material being preferably in the form of powder, granulate and/or tablets, said containment enclosure comprising a perimeter and a base and being characterized in that it comprises at its base, and eventually also around its perimeter, a plurality of separate sub-critical spaces (603) for catching spilled plutonium-containing material.

Process for preparing nuclear fuel using a mixture containing uranium oxide, carbide or nitride and civilian or military origin plutonium in the form of, respectively, plutonium oxide, carbide or nitride, as well as possibly other actinides such as americium, neptunium, and/or curium, the process being characterised in that:

• said mixture has a plutonium concentration not higher than a maximum guaranteed plutonium concentration, and an isotopic composition within a predetermined envelope, and
• throughout the whole process, substantially all of this mixture and any material resulting from it are contained within a set of vessels dimensioned so as to be sub-critical even if completely filled with said mixture at said maximum guaranteed plutonium concentration, with any isotopic composition within said predetermined isotopic envelope, for any density up to a predetermined maximum guaranteed process density and under the most negative neutron reflection and moderation conditions.