Bibliographic synthesis of the experimental and numerical German and French research programs concerning slug impact
Résumé
Slug impact is considered as a potential risk for PWR power plants in case of a severe accident. A loss of coolant can cause the degradation of the core and its melting. By falling down in the water remaining in the lower plenum, the corium transfers quickly its energy to the water which vaporizes and causes a steam explosion. The explosion may be powerful enough to accelerate upwards all the materials above the explosion zone and causes, in turn, a slug impact.
During this process, the mechanical energy of the explosion is transformed into kinetic energy for the slug. If the slug is energetic enough, it can crush and fail the upper structures. Then the mixture of slug and upper structure pieces may hit the upper head vessel. The impact may fail the upper head or part of it and thus create missiles, ung upwards thanks to the remaining energy.
The slug impact is studied by the german and french research centers FZK and CEA-Saclay. FKZ aims at the quantification of the maximum mechanical energy which would not lead to fail the upper head. They investigate this issue by means of the reduced-scale experiments BERDA.
The transfer of the experimental results to reactor dimensions using scale factors are based on similarity laws whose validity is checked thanks to the german test-facilities FLIPPER. The understanding of the slug material influence and the extrapolation to the corium is investigated with the french test-facilities SKIPPY.
In order to deepen the understanding of the impact process and to extrapolate the experimental results to other combinations of parameters, corresponding theoretical work is being performed with the code ABAQUS for the impact of solid structures and with the code CASTEM-PLEXUS developped by CEA-Saclay
for the impact of liquid projectile against solid structures.
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