Modelling of premixed layer formation in stratified fuel–coolant configuration

• Published in: Nuclear engineering and design 2021-07, Vol.378, p.111261, Article 111261
• Main Authors: Kokalj, Janez, Uršič, Mitja, Leskovar, Matjaž
• Format: Article
• Language: English
• Subjects: Configurations; Coolants; Explosions; Fuels; Fuel–coolant interaction; Modelling; Nuclear safety; Premixed layer formation; Qualitative analysis; Severe accident; Steam explosion; Steam explosions; Stratified configuration; Visual observation
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2021.111261

•Premixed layer formation in stratified fuel–coolant configuration is presented.•Model for premixed layer formation is developed.•Simulations of premixed layer formation and explosion are performed with MC3D code. 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. The purpose of our research was to improve the knowledge, understanding and modelling of the fuel–coolant interaction phenomena in the stratified configuration. In the paper, models for the premixed layer formation, based on the visual observations and some available mechanisms from the literature, are presented. Due to the uncertainties and the lack of detailed information, two different approaches were followed in the modelling. Both models and experimental observations were discussed and joined into the third model, which describes the considered phenomena the best. 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.