Publications Details

Late-phase melt progression experiment: MP-2. Results and analysis

Gasser, R.D.

In-pile experiments addressing late-phase processes in Light Water Reactors (LWRs) were performed in the Annular Core Research Reactor (ACRR) at Sandia National Laboratories. Melt Progression (MP) experiments were designed to provide information to develop and verify computer models for analysis of LWR core damage in severe accidents. Experiments examine the formation and motion of ceramic molten pools in disrupted reactor core regions. The MP-2 experiment assembly consisted of: (1) a rubble bed of enriched UO{sub 2} and ZrO{sub 2} simulating severely disrupted reactor core regions, (2) a ceramic/metallic crust representing blockage formed by early phase melting, relocation, and refreezing of core components, and (3) an intact rod stub region that remained in place below the blockage region. The test assembly was fission heated in the central cavity of the ACRR at an average rate of about 0.2 KA, reaching a peak molten pool temperature around 3400 K. Melting of the debris bed ceramic components was initiated near the center of the bed. The molten material relocated downward, refreezing to form a ceramic crust near the bottom of the rubble bed. As power levels were increased, the crust gradually remelted and reformed at progressively lower positions in the bed until late in the experiment when it penetrated into and attacked the ceramic/metallic blockage. The metallic components of the blockage region melted and relocated to the bottom of the intact rod stub region before the ceramic melt penetrated the blockage region from above. The ceramic pool penetrated halfway into the blockage region by the end of the experiment. Measurements of thermal response and material relocation are compared to the results of the computer simulations. Postexperiment examination of the assembly with the associated material interactions and metallurgy are also discussed in detail with the analyses and interpretation of results. 16 refs., 206 figs., 24 tabs.