Results of scoping tests in corium-water thermal interactions in ex-vessel geometry

Results of scoping tests are reported which were performed in the ANL/EPRI Corium Ex-vessel interactions (COREXIT) Facility located at ANL. These tests are examining issues related to containment loading (i.e., steam generation, H2 production, and debris dispersal) for hypothetical LWR accidents that are postulated to progress to the point of molten corium breaching the vessel bottom head and entering the reactor cavity. The geometry selected for these tests is a 1 : 30 linear scale of the Zion PWR containment design in which the cavity is connected to the containment volume by an open tunnel through which pass the in-core detector guide tubes. The effects of the corium-water mixing modes were investigated in the first two tests in the series. In test CWTI-1 the molten corium was ejected into water which filled the cavity mockup volume to one-half the passageway height. In CWTI-2, the molten corium was dropped atop the refractory base in the cavity mockup without the presence of water, and water was injected atop the corium melt immediately afterward as per accumulator discharge. These tests have shown significant differences in fuel fragmentation, steam generation rate, hydrogen production, and fuel dispersal. Particularly noteworthy was the significant amount of dispersal of both water and corium debris from the cavity mockup due to the initially rapid steam generation rate in CWTI-1