The supercritical carbon dioxide (sCO 2) heat removal system, which is based on multiple closed Brayton cycles with sCO 2 as the working fluid, is an innovative, self-propelling and modular heat removal system for existing and future nuclear power plants. Previous studies analysed its design, layout, control and operation. In addition, this study considers different sudden failures during the accident progress, e.g. failure of single sCO 2 cycles, control systems and valves. These abnormal conditions were investigated with the thermal-hydraulic system code ATHLET for a generic Konvoi pressurized water reactor. In most cases, the failure of a single sCO 2 cycle can be compensated. On the one hand, failure of the fans of the gas cooler leads to a pressure increase which may be mitigated by an inventory control system or cycle shutdown. On the other hand, unintended fan speed-up can cause compressor surge without adequate countermeasures. Furthermore, the system can operate under the cyclic blow-off from the steam generator safety valves when the relief valves are not available. Finally, the unintended closure of the valve which controls the steam flow through the compact heat exchanger triggers a fast cycle shutdown but a subsequent restart might be possible. • Transient simulation of a supercritical carbon dioxide heat removal system. • Successful operation in interaction with a pressurized water reactor. • Analysis of different sudden failures, e.g. of single cycles, control systems and valves. • Some failures are mitigated by the applied robust design of the heat removal system. • For other failures, fast interventions or further design or control improvements are proposed. [ABSTRACT FROM AUTHOR]