Coolability of UO2 debris beds in pressurized water pools: DCC-1 and DCC-2 experiment results

DCC-1 and DCC-2 (Degraded Core Coolability) have provided the first in-pile data for water-urania dryout heat flux and quench behavior. DCC-1, designed to test the laminar flow region of dryout, has displayed unexpected results. while the dryout fluxes at one atmosphere are approximately those predicted by many of the models, the pressure dependence of the dryout data is predicted by none of the models. The quench behavior of DCC-1 displays none of the fingering observed in out-of-pile experiments. The quench times extend for hours. The DCC-2 dryout data conforms in magnitude and pressure dependence with several of the models. In addition to global dryouts, in which the dry zone extends across the width of the bed, local dryouts were observed. These are zones of lower than average permeability which dry out and achieve stable temperatures without eliminating coolant flow to the bottom of the bed. The quench times in DCC-2 are only a few minutes long. Fingering, modified by the radially varying temperature of the dry particles, was observed