The ECO steam explosion experiments

Analyses of LWR core melt accidents show that in case of a steam explosion the reactor pressure vessel may experience a considerable mechanical load which however remains below the capabilities of the vessel. The ECO experimental series has been conducted with relevant melt masses (up to 18 kg) at the Forschungszentrum Karlsruhe to extend the data basis necessary for the analyses and to reduce the uncertainties (that had to be covered conservatively). Explosion pressures were measured as well as the Energy COnversion under well-defined conditions. The facility consists in principle of a piston and cylinder system. Molten alumina (Al2O3) from a thermite reaction was used to simulate the high temperature core melt. The melt is injected from above into a water pool which is situated in the piston. Under the explosion pressure forces, the piston moves downwards compressing a stack of crushing material with known forces. The energy conversion ratio was considerably increased after the first few tests by changing essential test conditions. The water-to-melt mass ratio was decreased and the melt jet was partly fragmented before it penetrated into the water. Under these conditions, the short-term peak pressures exceeded the registration limits of 50 and 100 MPa while the energy conversion ratio reached about 3%. (orig.)