The Auxiliary Building Controlled Area Emergency Exhaust Air Cleaning Units (ACU) should be taken into account in the accident analysis that the entire gaseous radioactive material is exhausted to the environment through the auxiliary building without any filtration until the pressure reaches a negative pressure, approximately -0.25 inch, water gauge, when the ACU operation is credited in the analysis. Thus, this paper performed thermal-hydraulic analysis using GOTHIC program and showed the exhaust flow from each room in the auxiliary building controlled area to maintain room pressure not greater than (-) 0.25 inch water gauge.