Aspects of heat transfer in containment spot cooling circuit

The passive emergency pressure decrease system (EPDS) in the floating KLT40-S RP NPP containment was studied at the large-scale experimental containment SPOT test facility. The containment was simulated as a tank of 59 m³ of volume and about 8 m height. Passive system cooling circuit was simulated in full scale including heat exchanger-condenser (HX-C), which is located in the containment model and a tank with water inventory evaporated to the atmosphere (V=25 m³). System power (120-600 kW) as a function of containment model pressure for various initial air pressures in the model (40-170 kPa, abs) was obtained. The conditions causing various types of unstable flows (general-circuit, geyser), first associated with the lower pressure in the cooling circuit and high values of dρ/di (where ρ is steam-water mixture density at the riser section, i is coolant enthalpy at HX-C outlet), and with existence of cooling circuit riser section (∼10 m), were studied by experiment. The technical solutions increasing system effectiveness and the steam discharge device (SDD), which eliminated condensation hydraulic shocks, were proposed. The comparative experiment and calculation results obtained using KUPOL-MT code were presented. (author)