[en] During the period 1987-1993 three series of tests on interactions between molten fast reactor fuel and liquid sodium were conducted in the Molten Fuel Test Facility operated by AEA Technology at Winfrith Heath in the UK. In all the tests the molten fuel was simulated by the products of a uranium thermite reaction at 3600 K. Quantities of up to 24 kg of melt and 1200 kg of sodium were involved. The mechanical energy of the interactions was measured, and observations of their consequences were made. The experiments investigated: The effects of scale and pressure on interactions when contact was in simple geometry; The effects of interactions under contact conditions closely representing a hypothetical blockage accident in a fast reactor subassembly; The extent of penetration of molten fuel into an adjacent initially intact subassembly. It was found that the larger the scale and the closer the sodium temperature to saturation the more energetic the interaction between molten fuel and coolant, but the more restricted the geometry of the contact the less energetic the interaction. Penetration of molten fuel into adjacent subassemblies was found to be unaffected by the presence of sodium. Overall the results lead to the conclusion that the propagation of damage from the affected subassembly to its neighbours by this mechanism is unlikely. (author)