The Modified Dynamic Simulator for Nuclear Power Plants (MDSNP) code is applied to predict the one-dimensional thermal-hydraulic response of the shutdown heat removal system (SHRS) in the Sodium Advanced Fast Reactor and to study the effect of uncertainty and variation in certain design parameters of the SHRS. An example of the use of the code as a design tool to optimize the performance of the SHRS is given. The results show that when neither the direct reactor auxiliary cooling system nor the reactor air cooling system (RACS) is available to remove decay heat, the intrinsic thermal capacity of the pool limits the hot pool to a temperature below the sodium boiling temperature until 30 h after reactor scram. The peak hot pool temperature when only the RACS is available is 710°C, which is ∼22°C below the American Society of Mechanical Engineers service D condition. The changes in emissivity and ambient air temperature slightly affect the time at which an overflow occurs, the temperature histories of the pools, and the temperature difference between the pools. A higher elevation of components such as intermediate heat exchangers and direct reactor heat exchangers is found to increase the available hydrostatic head, which, in turn, reduces the temperature difference between the two pools.