The use of the high temperature SCWO effluent for energy purposes has been studied in the literature. In this work, a SCWO system with an external shell (double-shelled reactor/DSR) will be used to heat a thermal fluid (pure water) beyond its critical point in order to run electricity generators. At the same time, this counter current stream of water through the external shell cools down the reacting stream in the SCWO reactor and controls the reactor's temperature. This allows the treatment of high concentrated waste without exceeding temperature safety limits. In order to compare the performance of a double-shelled reactor with a conventional one, both reactors were built at laboratory scale. The performance of the DSR was analysed by modifying some of its operating parameters such as the initial waste concentration or the coolant flowrate. Moreover, a model of the DSR was built and validated by several tests that allowed us to study the reactor's operation beyond the tested conditions.