In advanced water-cooled nuclear reactors, the passive safety systems are preferably used to achieve enhanced safety during accidental conditions. The passive containment air cooling system (PCACS) is one of the safety systems used to remove heat from the containment during accidental conditions like a loss-of-coolant accident, station blackout, etc. in advanced nuclear reactors and small modular reactors with steel containment. The PCACS uses the buoyancy-driven flow of air to remove heat from the steel containment to avoid the over pressurization of the steel containment shell. It is extremely important to understand the natural convection around the containment shell so as to evaluate the performance of the PCACS.

This paper presents an experimental investigation of the passive containment air cooling of an experimental test setup having a geometry very similar to that of an actual reactor. The air-side transient natural convection characteristics around the experimental containment system are studied in detail based on the temperature readings. The measured average heat transfer coefficient is compared with that predicted using well-known correlations available in literature. This study provides a better understanding of the natural convection flow around the containment and will help in further numerical investigations for actual-scale containments.