TRACE code simulation of the interaction between reactor coolant system and containment building with passive heat removal system

Several integral and separate effect test facilities are constructed around the world on scaled-down bases to simulate the complex thermal-hydraulic phenomena of the commercial nuclear power plant. PKL is one of the integral test facilities of four loops of western-type KWU pressurized water reactor (PWR) with 1:1 in height scale and 1:145 in volume and power scale. Using the PKL facility, a large database has been created through numerous experimental tests investigating transients such as Loss of Coolant Accidents (LOCAs) and station blackouts. On the other hand, the PASI facility is a separate effect test facility that has been built at LUT University to simulate the Containment Wall Cooling (CWC) passive safety system for the AES-2006 NPP type at a 1:2 height scale, 1:281 in volume, and 1:141 power scale. This paper utilizes the newly released US-NRC TRACE (version 5 - patch 7) system thermal-hydraulics code to investigate the thermal hydraulic interaction phenomena between the reactor coolant system (RCS) and containment building, referring to the PKL facility as the RCS and the PASI facility as the containment heat removal system. During LOCAs, the pressure in the containment is a key parameter to evaluate the core behavior and the passive containment cooling system (PCCS) performance. This study emphasizes the ability of CWC to reduce the pressure in the containment and remove the core residual heat during LOCA accidents. Additionally, it contributes to evaluating the capability of system analysis codes to model the complex interaction between the RCS and containment building.The TRACE model for the PASI facility has been validated against the respective experimental results. Then, the PKL G7.1 test has been utilized to validate the PKL TRACE model during the hot leg SBLOCA test. The results of TRACE simulations show good agreement with experimental data, including natural circulation behavior, core exit temperature (CET), and peak cladding temperature (PCT). After the validation stage, PKL and PASI TRACE models are coupled to create a virtual experimental test. The coupled model uses the CWC scaled up from the PASI facility. During SBLOCA, steam released from the primary loop to the containment is condensed on the CWC heat exchanger tubes. The results illustrate the complex feedback interaction between the RCS and containment building. The CWC can reduce the pressure in the containment during LOCAs and extract a large amount of the core residual heat. This research can provide a better understanding of the natural circulation and flow instability of the containment passive cooling system, and its influence on the RCS performance. As well as, it provides additional reference data to system code users for the further development of scaling and coupling methodologies. The coupling approach evaluates the capabilities of TRACE code for modeling the containment building.