The aim of the paper is to highlight the research priorities for the sodium vapour explosion modelling with the fuel-coolant interaction codes. Several simulations were performed with the MC3D code (IRSN, France) to support the qualitative and quantitative assessment of the modelling challenges. The main findings are: (1) the MC3D code is capable to cover vapour explosions in sodium, (2) the need for super-critical sodium tables is indicated, (3) the vapour explosion in sodium might be considered as an intensive premixing phase, (4) the experimentally observed limitation of the pressure to some MPa is also observed with simulations, (5) in future the thermal fine fragmentation modelling might be needed and (6) an experimental study of the heat transfer around the fine fragments shall be performed.
COBISS.SI-ID: 13554691
In the frame of safety studies for the demonstration-scale sodium cooled fast reactors, it is important to estimate the risk of vapour explosions. The modelling capabilities of the fuel-coolant interaction codes to study the vapour explosion phenomenon in light-water reactors were already proven in the frame of international programmes. Because of large differences in the thermo-dynamical and physical properties of sodium compared to water, the applicability of the fuel-coolant interaction codes for sodium must be investigated and the models adapted to sodium. The MC3D code (IRSN, France) is one of the codes that have the capabilities to simulate the fuel-sodium interaction. In the presented paper, the first investigation of the MC3D code applicability to the vapour explosions in sodium is presented. The results indicate that the strength of vapour explosions in sodium seems to be intrinsically limited to some MPa.
COBISS.SI-ID: 32369959
In the recent fuel–coolant interaction experiments performed in the stratified configuration at the SES and PULiMS facilities (KTH, Sweden), a premixed layer of ejected melt drops in water was clearly visible and was followed by strong spontaneous steam explosions. In the paper, model for the premixed layer formation, based on the visual observations and some available mechanisms from the literature, is presented. The developed model was implemented into the MC3D code (IRSN, France) and validated against the experimental results. The presented analyses demonstrate the model capability to describe the premixed layer formation in a qualitative agreement with the available experimental data.
COBISS.SI-ID: 62091523
The duration of the stratified steam explosion is studied by the analysis of experimental observations in the PULiMS and SES (KTH, Sweden) tests using simulation results obtained with the MC3D code (IRSN, France). The explosion characteristics are analysed by varying the available melt mass in the premixed layer, the triggering position, the melt droplet diameter, the void fraction in the premixed layer, the void fraction in the water above the premixed layer and the size of the fine fragments. The analysis showed that longer explosion duration for the experiments with strong explosions cannot be predicted solely by varying the premixed layer conditions. A significant increase of the explosion duration could be obtained only by increasing the size of the fine fragments, which depends on the nature of the explosion. Thus, the observed discrepancies between the experimental results and simulations can be explained by the fact that in strong stratified steam explosions there is also significant melt-water layer mixing during the explosion propagation.
COBISS.SI-ID: 32558119
The backward facing step geometry (BFS) is a representative geometry for sudden expansions in pipe, duct and channel flows. While this type of geometry by itself is not a part of engineering components, the flow separation and the accompanying flow features present in a BFS are of great importance when designing manifolds, heat exchangers or fuel bundles. In the frame of EU Horizon 2020 project SESAME, an extensive effort has been put forward to gain more insights into the flow and thermal features in a BFS geometry for low-Prandtl number fluids. In this paper, also a direct numerical simulation (DNS) results are shown. Similar to the experiment, the shape of the outflow is a square and the average flow is three-dimensional. Conjugate heat transfer DNS is performed for the heated solid walls. Finally, this reference DNS data is used to validate a LES and an advanced RANS modelling approach.
COBISS.SI-ID: 32226855