Freezing of a thermite melt injected into an annular channel experiments and recalculations

Abstract

The analysis of hypothetical accidents of liquid metal cooled fast breeder reactors (LMFBR) shows that the reactor core can under certain circumtances undergo melting. The movement and freezing behavior of the molten core material are of primary importance for the subsequent course of the accident. To investigate the characteristics of freezing and crust formation of a melt penetrating into cold structure, a series of out-of-pile experiments was performed using a simple cylindrical geometry. In the experiments the molten fuel was simulated by a thermite melt that was formed by the reaction of iron oxide and aluminum and was forced into a freezing channel. The movement of the melt was observed by X-ray cinematography and on-line instrumentalation. Post-test examination supplied information about the distribution of the relocated material and the formation of the crusts. The tests were then analyzed with the multicomponent computer code BUCOGEL. The test results show that the freezing behavior of the thermite melt is comparable to that of a uranium oxide/stainless steel mixture as used in in-pile tests conducted in similar geometry. The results of the thermite tests are therefore regarded as suitable to validate the relocation and freezing modules of computer codes describing whole-core accidents.