The aim of the investigation presented in this work was to realise complex calculations of a new, combined water-steam system with peak-load hydrogen turbine to be applied in nuclear units with gas-cooled reactors. The system’s characteristic feature is the presence of two heat sources: a nuclear steam generator; and a hydrogen-oxygen combustion chamber. The main idea is to create a system capable to operate in two modes, with one or two heat sources, which leads to a significant output change. The investigation included also the overall efficiency of conversion of the nuclear energy, assumed the heat needed for producing hydrogen and oxygen comes from such a source. This part of the work included an analysis of the rationality of hydrogen production and utilisation. An additional aim of the research was to determine the optimal solution regarding the system performance and the capability of its technical realisation. The obtained results are promising: the system performance is very high, and its operating parameters are technically realisable in today’s conditions. In addition, it enables an emission-free, dispatchable electricity generation during the daytime demand peak.