Monte carlo analysis of SNEAK-12A core disruption in liquid-metal fast breeder reactors - The path for innovative severe accident studies in ZPR

The field of recriticality possibilities in both light water reactors and fast reactors remains an important area of R&D, and in particular from the neutronics point of view. Future experimental programs to be implemented in forthcoming zero power experimental facilities should be able to deal with enhanced capabilities for simulating sequences of severe accidents, leading to significant structural damages, and their impact on power excursion and possible reciticality. However, existing programs have been realized, but not fully intepreted at the time. A new computational benchmark is here introduced based on the SNEAK-12A critical assembly experiments. These experiments studied the reactivity effects of different core disruptions in LMFBRs due to severe accident which results in core degradation, i.e. fuel meltdown and materials relocation in the core. The different stages of the core damage progression during a severe accident were modeled by a series of representative core configurations. These configurations are calculated using advanced Monte Carlo codes such as TRIPOLI and Serpent, and include effective multiplication factor, flux and reaction rates distribution and energy spectrum. The calculated results are compared to the experimental values and show good to very good agreement for reactivity effects. Additional quantities have been modeled, such as fissile detectors positioned in various core areas. The study demonstrates that they behave differently during the accidental sequence, hence opening new possibilities for core monitoring. The ultimate goal of the present study is to prepare a more comprehensive benchmark to be shared within an international context, as to enlarge a future experimental database for both light water and fast reactors, taking profit from innovative modeling and experimental capabilities.