Thermal-hydraulic responses in the station blackout experiment conducted at the IIST facility are simulated through the use of the advanced system code RELAP5/MOD3. Typical behaviors occurring in the IIST station blackout transient are characterized by secondary boiloff, primary saturation and pressurization, and subsequent core uncovery and heatup. As the coolant inventory within the steam generator secondary system boils dry, the primary system pressure increases as a result of degradation of the heat removal ability of the steam generator secondary side. This pressurization phenomenon causes the pressurizer safety valve to open and the primary coolant to deplete through the valve, causing the core to eventually become uncovered. The same response can be exactly simulated by the current model. The current calculated results show fairly good agreement with the experimental data, but the timing of the events occurring in the station blackout transient is calculated earlier than the measured value. The overall comparison of key parameters between the calculated results and IIST test data, however, reveals that the current RELAP5/MOD3 model can provide reasonable station blackout modeling for simulating longterm system behavior.