CRISTAL: a french criticality code package to assess nuclear installation criticality safety

For more than thirty years, CEA, IRSN and the French nuclear industry have been combining their efforts to finance, develop and validate computer codes to assess the criticality safety concerns of nuclear installations, transport casks, and reprocessing facilities. As one of the major world fuel vendors, Framatome ANP is deeply involved in defining code developments which incorporate feedback from both users and customers. The result of these continuous efforts is the evolutionary CRISTAL code. The CRISTAL package was developed as an easy-to-use system using cross-section libraries (JEF 2.2 and CEA93), well-established computer codes (APOLLO2, MORET 4 and TRIPOLI-4) and including a Graphical User-Friendly Interface. The APOLLO2 computer code, a spectral code used for evaluating the basic characteristics of fuel assemblies, has been upgraded to perform criticality safety calculations. The MORET 4 computer code is a neutron simulation code in three dimensions which uses the multigroup formalism for cross-sections and the Monte Carlo method to solve the Boltzmann equation. Through the years, the CRISTAL package has been improved to take into account both the growth of its validation database and the increasing user requirements. Today, CRISTAL V0 is an up-to-date computational tool incorporating the comprehensive APOLLO2 and MORET 4 computer codes; CRISTAL V0 is the result of more than five years of development work focusing on theoretical approaches and on the implementation of user-friendly graphical interfaces. Thanks to its broad validation database, CRISTAL V0 provides outstanding accuracy of criticality evaluation for configurations covering the entire fuel cycle life (i.e. from fuel enrichment, pellet/assembly fabrication and transport casks to fuel reprocessing). With more than a thousand benchmark/calculation comparisons, uncertainties can be deduced for various file media, fissile shapes, fissile process interactions, neutron-poisoning screens and material reflectors. These uncertainties, combined with suitable modelling features, ensure confidence in the CRISTAL results when justifying sufficient safety margins. After a brief description of the calculation scheme and the physics algorithms used in the codes, various industrial applications encountered in a UO2 fuel fabrication plant will be discussed. (authors)