Composite fuels. Neutronic criteria for selection of matrix, core control, transients, and severe accidents

The nuclear fuel context in France, closely linked to reprocessing, today poses numerous problems insofar as a combination of several factors has led to an increase in the stocks of plutonium and irradiated fuels awaiting reprocessing. One solution proposed here is the use of composite fuels in inert matrices, which would enable avoiding 238Pu conversion to 239Pu. As ceramic matrices are transparent to neutrons, the study has been focused on CERMETs. The analysis of certain neutronic criteria, such the Doppler coefficient and the draining coefficient resulted in the selection of a metallic Zry matrix. A certain number of calculations show that the core of a 900 MWe PWR is controllable, providing burnable absorbers are used in association with very precise modes of management. Finally, a preliminary study of severe accidents is performed, which demonstrates that, according to which assumptions are made, conditions can differ considerably. The problem of recriticality is crucial. (author)