<p>The purpose of the present study is to evaluate and improve the capability of the SIMMER code to demonstrate severe accident mitigation in Sodium-cooled Fast Reactors. The French concept of mitigation strategy consists of a vertical transfer tube dedicated to facilitate the discharge of molten and degraded fuel from the core center region and guide it towards the core catcher, where re-criticalities can be avoided and long-term cooling can be provided.&nbsp; The numerical representation of the material transfer inside the transfer channels is carried out with SIMMER code. SIMMER is a multi-velocity field multi-phase Eulerian fluid-dynamics code that is able to analyze the progression of severe accidents postulated in SFRs. By using the advanced multi-phase modelling option of the code, the particle-size solid debris is treated with an independent momentum phase in French safety study approach. This modelling choice is encouraged for the simulation of ULOF type transients in French SRF core design where low enthalpy degraded fuel is expected to manifest in solid fragments. The motivation is to provide a more precise description of complex solid-gas-liquid flows inherent to the discharge phenomenon when degraded core mixture is highly abundant in solid debris components. Applying this new particulate approach in SIMMER code requires the reevaluation of current SIMMER fluid dynamics modelling. Our focus is to assess the applicability of SIMMER momentum models to account for the peculiar behavior of a purely particulate phase, and to implement new correlations where improvement is necessary. The assessment is performed through the investigation of simplified test cases that can be associated to reactor scenarios in severe accident mitigation strategy. In this context, a set of validation test cases are presented and concluding on the identified modelling gaps, a new set of particle dynamics models in SIMMER code is introduced in this paper. The evaluation procedure applied here to demonstrate the performance of the new modelling set incorporates analytical, empirical and experimental comparison. It shows that the new modifications in SIMMMER code bring significant improvements in predicting the discharge rate of degraded core materials.</p>

Preliminary Version of Improved Particle-Flow Model in Simmer-v for an Alternative Severe Accident Modeling Approach in Sfrs

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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