[en] The base of the physical model of the FCI in discussion are the shock tube experiments performed with UO₂ and Na. The experiments demonstrated that the process of 'vapour explosion' in constrained configurations consists of successive cycles. According to the experimental results, the interaction model described here divides each cycle into three phases: Fuel-Coolant-Contact (Phase A), Ejection and reentry of the coolant (Phase B), Impact and Fragmentation (Phase C). The results of some calculations, performed for different values of the system pressure resp. of the coolant bulk temperature, are compiled in plots displaying the series of successive ejection events of an interaction; the plots represent the ejection height and the corresponding pressure in the vapour volume versus time. The pressure peaks mark the impact pressure pulse resp. the vapour pressure immediately after contact, which-ever is greater; the acoustic pressure peak of Phase A has not been plotted. The third and the following cycles reveal the oscillating reentry behaviour. A physical model has been proposed to describe fuel coolant interactions in shock-tube geometry. The corresponding code is presently in an advanced state of development. A principal feature, of the code is the consistent application of the Fourier-equation throughout the whole interaction process; this reveals some peculiarities which do not become evident otherwise. The two dimensional representation of the coolant flow provides the basis for a fragmentation mechanism, thus relieving from the necessity to introduce the fragmentation as an input parameter. These features may indicate a step towards a more realistic comprehension of the subject