Small Modular Reactors (SMRs) are currently being developed and licensed in many countries. The innovations in the designs provide many significant features, such as decreased construction cost and time, enhanced safety, modularity, possibility of factory production etc. Several new SMR designs are based on the concept of an integral Pressurized Water Reactor. One of such designs, namely the NuScale SMR was selected for this analysis. An input model was developed from scratch for the RELAP/SCDAPSIM code using publicly available data from the NuScale Final Safety Analysis Report provided by the U.S. NRC and some validation tests have already been conducted. An extremely severe event is analyzed and discussed in the current work. It is an inside containment Loss of Coolant Accident followed by failure of both the Emergency Core Cooling System and the Decay Heat Removal System. The simulation was conducted for 86400 s (24 h) with the core damage starting after ~4.8 h, which is comparable to the results for similar scenarios presented in the references.