FOUNDATIONS FOR THE DEFINITION OF MOX FUEL QUALITY REQUIREMENTS

The quality of uranium-plutonium mixed oxide (MOX) fuel, as of any nuclear fuel, depends on the design optimization and on the fabrication process stability. The design optimization is essentially based on feed-back from irradiation experience through engineering assessment of the results; the stability of the process is necessary to justify minimal uncertainty margins in the fuel design. Since MOX fuel is quite similar to UO2 fuel, the lessons learned from UO2 fuels can complement the MOX experimental data base. MOX is however different from UO2 fuel in some respects, among others: the industrial fabrication scale is a factor 10 lower than for UO2 fuel, the fuel enrichment process takes place in the manufacturing plant, the radioactivity of Pu imposes handling constraints, Pu ages quite rapidly, altering its isotopic composition during storage, the incorporation of Pu alters the material physics and neutronic characteristics of the fuel. In this perspective, the paper outlines some quality attributes for which MOX fuel may or even must depart from UO2 fuel.