Neutron radiography flow visualization of liquid metal injected into an empty vessel and a vessel containing saturated water

Neutron radiography was used to observe the behavior of molten lead-bismuth alloy injected into a thin (10-mm) semicircular vessel, which was empty or contained saturated water. The fluid velocity distribution for the melt in jected into the empty vessel was successfully measured using particle image velocimetry (PN). The numerical analysis for this case using the FLOW-3D c ode revealed that the wall heat transfer attenuates the rotational speed of swirls that were formed during the melt injection. The melt-coolant intera ction experiment demonstrated several features of molten fuel and coolant i nteractions in the reactor pressure vessel lower head. The violent vapor ex pansion occurred at the initial melt impact on the saturated pool water A o ne-dimensional model predicted the observed behavior well by assuming the a diabatic expansion immediately after art instantaneous heat transfer during the first melt coolant contact. A crust was formed between the melt and co olant by the heterogeneous distribution of the coolant and pool melt. The c onvective velocity distribution in the pool melt was measured well by the P IV.