Modelling of debris bed cooling

Experiments have been performed in investigating the flooding phenomena of steam and water in isothermal homogeneous beds of particles with an overlying two-phase pool. The beds were constructed by spherical particles of 8, 16 and 39 mm diameter and cylinders 16 mm in diameter and length in cylindrical test sections 15 and 30 cm in diameter. Bed depths of 15 cm and 30 cm were employed. Water was injected into the overlying pool at saturation temperature or with 50 degree C of subcooling. A new flooding correlation was obtained which provides improved prediction of dryout heat flux for internally heated beds of large particles (d > 1 mm). Limited study of multi-dimensional effects was also included in the experimental program. A theoretical model, based upon relative permeabilities for twophase flow, is proposed to study the flooding phenomena in the homogeneous beds. The prediction of flooding locus was found to agree rather well with the new flooding locus was found to agree rather well with the new correlation. The analytical form of the flooding lines have also been carried out in both high inertial flow region (pure turbulent) and Darcy flow region (pure laminar). The flooding model has also been applied to estimate the dryout heat flux of particle beds. The predictions agree very well with the experimental data not only within the large particle region (d > 1 mm) but also in the small particle region (d < 1 mm). An one-dimensional two-temperature model has been developed to investigate transient behaviour during cooling of the debris beds by bottom flooding. The calculated quenching front speed was compared with the available experimental data. Quenching with the Zr-water reaction was also studied. A significant temperature build-up in the solid was found when the chemical reaction is present