Safety and criticality analysis for storage and transport of spent MOX fuel

Within the framework of spent fuel reprocessing in La Hague plant, the authorization to unload these fuel assemblies into a pool is obtained further to studies relative to their transport in cask. As regards the criticality, the MOX type fuels display several specificities with respect to uranium assemblies (UOX). In actual fact, whereas the UOX type assemblies are characterized by their 235U enrichment, the MOX assemblies are fabricated from a mixture of plutonium batches of various origins and with different isotopic compositions: this leads to define fabrication fields with ranges of values for the Plutonium content and isotopic composition parameters, to which are added the fluctuations of parameters which have a great incidence on the assembly reactivity. The MOX designs are therefore diversified and the authorizations for transport and acceptance in pools can be obtained per type of concept. However, in order to enlarge its approach, COGEMA has developed a safety-criticality demonstration aimed at encompassing the widest possible range of MOX fuel assemblies so as to reduce the number of generic authorizations without any requirement as to the minimum burnup. (author)