Advanced small and large core distortion modeling in ZPR to assess core recriticality scenarios of SFR core degradation sequences

Severe accident and their impact on core recriticality is still a pending problem in both thermal and fast lattices. Several lacks in core physics understanding need to be addressed, through, for example, dedicated experimental programs in ZPRs. A new computational benchmark is introduced based on the SNEAK-12A critical assembly experiments in the 80’s. 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 as TRIPOLI and Serpent, and include effective multiplication factors, flux and reaction rates distribution and energy spectrum. The results are compared to the experimental measurements. The ultimate goal of the study is to assess recriticality possibilities in both light water reactors and fast reactors in a future experimental programs that could be implemented in adapted ZPR. The main objective of this work is to evaluate two scenarios of SFR core degradation sequences, small and large core distortions. The sequence leading to core damage is initiated by a total sodium dry out of several channels, which is then followed with small and large fuel compactions around the core mid plane. At the final stage the compacted fuel is relocated to the bottom part of the core, where it forms a molten pool representative configuration. The objective of the work is included in a more general framework of developing a new approach for experiments design in the frame of severe accidents studies in LWRs and FRs. The underlying idea is to build a full program of tests in a dedicated facility and to develop innovative approaches to manage the measurement of reactivity effects and local power distributions.