The transition of power systems to mitigate climate change can be facilitated by producing hydrogen and synthetic methane from renewable and nuclear power sources. This enables long-term energy storage and provides clean fuels for electricity generation and thermal energy. This paper evaluates the performance of nuclear power plant and synthetic methane production and storage, which is especially prospective in the Baltic region, because allow utilize the existing gas infrastructure, that includes a gas pipeline transmission and distribution network, gas power plants and a large underground reservoir. We use power systems optimization model, which include sub-models of renewables power sources and interconnections with Scandinavia and Poland and is supplemented by model of modular nuclear powerplant. The assessment of gas amount and costs, required capacity of plant to maintain energy balance, determining the required investments represents the main contribution of this paper. The conclusions can be used as guidelines when planning the development of electricity infrastructure.