ENHANCEMENT OF DRYOUT HEAT FLUX IN A DEBRIS BED BY FORCED COOLANT FLOW FROM BELOW

In the design of advanced light water reactors (ALWRs) and in the safety assessment of currently operating nuclear power plants, it is necessary to evaluate the possibility of experiencing a degraded core accident and to develop innovative safety technologies in order to assure long-term debris cooling. The objective of this experimental study is to investigate the enhancement factors of dryout heat flux in debris beds by coolant injection from below. The experimental facility consists mainly of an induction heater, a double-wall quartz-tube test section containing a steel-particle bed and coolant injection and recovery condensing loop. A fairly uniform heating of the particle bed was achieved in the radial direction and the axial variation was within 20%. This paper reports the experimental data for 3.2 mm and 4.8 mm particle beds with a 300 mm bed height. The dryout heat density data were obtained for both the top-flooding and the forced coolant injection from below with an injection mass flux of up to 2.5 kg/m(2)s. The dryout heat density increased as the rate of coolant injection increased. At a coolant injection mass flux of 1.0 kg/m(2)s, the dryout heat density was similar to 6.5 MW/m(3) for the 4.8 mm particle bed and similar to 5.6 MW/m(3) for the 3.2 mm particle bed. The enhancement factors of the dryout heat density were 1.6-1.8.