Investigation on passive decay heat removal in advanced water cooled reactors

For future advanced water cooled reactor designs passive safety systems should be investigated in respect of their feasibility and functional performance. The Research Center Karlsruhe and the Technical University of Karlsruhe have proposed a composite containment concept which copes with severe accidents. One essential of this concept is the decay heat removal from the containment by natural air convection and thermal radiation in a passive way. To determine the coolability of such a passive cooling system and to study the physical phenomena involved, experimental separate-effects investigations are under way in the PASCO test facility which is a one-sided heated rectangular channel. In addition numerical calculations are performed by using the one-dimensional code PASCO and the three-dimensional thermal-hydraulic code FLUTAN. Experimental results in respect to the distribution of the fluid velocities, fluid temperatures and wall temperatures are presented. Based on the experimental data the essential contribution of thermal radiation to the total heat transfer is illustrated. A comparison is made between the experimental data and code predictions. The deficiencies and needs for further research are being discussed. From the results achieved so far it has been found that the passive containment cooling by natural air convection coupled with thermal radiation is very promising. A medium-scale integral test facility MOCKA is presently under design and will serve to study the integral performance of the passive decay heat removal system proposed and to investigate the coolability limits by natural air convection coupled with thermal radiation under all conceivable boundary conditions. (author). 12 refs, 10 figs, 2 tabs