HEAT-TRANSFER ANALYSIS OF THE PASSIVE RESIDUAL HEAT REMOVAL SYSTEM INROSA AP600 EXPERIMENTS/

The passive residual heat removal (PRHR) system in the Westinghouse AP 600 advanced passive reactor design is a natural-circulation-driven he at exchanger cooled by the water in the in-containment refueling water storage tank (IRWST). During the experiments, which simulated small-b reak loss-of-coolant accidents in the AP600 reactor using the ROSA-V L arge-Scale Test Facility (LSTF), the PRHR system heat removal rates we ll exceeded the core decay power soon after the actuation of the PRHR. This resulted in continuous cooldown and depressurization of the prim ary side. The PRHR heat transfer performance in these experiments was analyzed by applying heat transfer correlations available in literatur e to the PRHR heat exchanger tube bundle. Also, the three-dimensional natural circulation in the IRWST was simulated numerically using the F LUENT code. The total heat transfer rate of the PRHR was predicted wit hin 5% of the measured value. The fluid temperature distribution in th e IRWST was also predicted well except that the elevation of the therm ally stratified region was underpredicted. The calculated flow pattern in the IRWST suggests that the atypical IRWST geometry in the LSTF ma y have affected the PRHR heat transfer performance during the experime nts only a little.