Burnup credit implementation for transport and storage casks of irradiated UO2 fuel assemblies - Presentation

TN International currently uses the BUC method for the design of casks dedicated to the transport of PWR UO2 used fuel assemblies. As long as the fuel enrichment of the PWR fuel assemblies was sufficiently low, a simplified BUC method based on the sole consideration of 8 major actinides and the use of a simplified axial burnup approach was satisfactory to cover the needs without necessity to design new casks. Nevertheless, the continuous increase of the fuel enrichment during the last decade has led TN International to continue the investigations on an improved BUC method in order to limit both the increase of the neutron poison content in the new basket designs and the burnup constraints attached to the acceptability of the fuel assemblies for transport. The strategy of TN International was then to take benefit of the reactivity reserves, which might be gained by considering the main fission products (103Rh, 133Cs, 143Nd, 149Sm,152Sm and 155Gd) that make up 50% of the negative reactivity of all fission products and more realistic axial profiles of burnup instead of uniform axial burnup profiles . The \"BUC\" calculation route for PWR UO2 used fuel is based on the connection of the French depletion code DARWIN and the French Criticality Safety Package CRISTAL V1 which are developed by the CEA and the IRSN in collaboration with French nuclear industry. French BUC experimental programs have been separately performed in Cadarache (France) and in Valduc (France) in order to validate respectively the DARWIN depletion code and the CRISTAL V1 Criticality Safety code system. The aim of this article is to present the improved BUC method implemented at TN International for the criticality safety assessment of transport and storage casks.