抄録
In case of a Hypothetical Core Disruptive Accident (HCDA) in a Liquid Metal Reactor, the interaction between fuel and liquid sodium creates a high pressure gas bubble in the core. The violent expansion of this bubble loads the vessel and the internal structures, whose deformation is important. The experimental test MARA10 simulates a HCDA in a mock-up schematising simply the reactor block of a Fast Breeder Reactor (external vessel and roof as well as the main internal structures of the reactor). The vessel is filled with water, topped with an air blanket. The test is fired using an explosive charge. This paper presents a simulation of the MARA10 test with the fast dynamics code EUROPLEXUS. The computed results are explained by means of an analysis of the pressures, gas fractions, fluid velocities, displacements, strains and stresses. The explosive charge in the centre causes the propagation of a pressure wave which impacts first the radial shield, the diagrid and the Above Core Structure base and later the vessel bottom and vessel lateral wall and finally the roof. The bubble gas expands in the central zone confined by the internal structures and afterwards it escapes in the rest of the mock-up by the narrow space between the ACS and the shield. Water vaporises out of the radial shield, below the diagrid and in the ACS. The air layer is compressed under the roof by the water pushed upwards by the explosion. Very soon, the diagrid moves down, the radial shield goes away and the ACS base goes up. Then the vessel base moves down and the lateral wall goes away, thus creating a lower bulge. The ACS lateral wall buckles, the ACS top goes up, thus pulling up the rest of the roof. Finally, an upper bulge creates in the upper part of the vessel lateral wall and the ACS base changes curvature.
