Janez Kokalj, dr. Mitja Uršič and dr. Matjaž Leskovar from the Reactor Engineering Division at Jožef Stefan Institute published the article »Modelling of premixed layer formation in stratified fuel–coolant configuration« in the journal Nuclear Engineering and Design.

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, a model for the premixed layer formation in stratified fuel–coolant configuration, based on the bubble formation and collapse mechanism 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. The indirect comparison of the simulated premixed layer with the SES S1 and PULiMS E6 experiments via the strength of vapour explosion shows underestimation in simulations’ explosion strength. This indicates possible contributions to the vapour explosion from the classical melt jet breakup and additional mixing during the explosion itself.

Figure: Comparison of steam explosion development for different trigger position. Red colour represent the pressure pulse.