Review of Experimental Results on Light Water Reactor Core Melt Progression

This paper reports on results from integral-effects core melt progression experiments and from the examination of the damaged core of the Three Mile Island Unit 2 (TMI-2) reactor which are reviewed to gain insight on key severe accident phenomena. The experiments and the TMI-2 accident represent a wide variety of conditions and physical scales, yet several important phenomena appear to be common to core melt progression. Eutectic interactions between core materials cause the formation of liquids and loss of original core geometry at low temperatures ({approximately}1500 K) in a severe accident. The first liquids to form are metallic in nature, and they relocate to lower elevations in the core, where they may freeze into a crust that forms a partial flow blockage. At temperatures above {approximately}2200 K, fuel liquefaction causes fuelbearing debris to accumulate in the core above the metallic lower crust. The liquefied material oxidizes in steam as it relocates, and the accumulated melt can incorporate unmelted fuel rod debris.