R4 nuclear reactor was a nuclear reactor built at Marviken, Vikbolandet and the fourth nuclear reactor built in Sweden. It was heavy water moderated and intended for the dual role of 130MWe of power generation as well as plutonium production. It had a central role in the Swedish nuclear weapon programme. During the mid 1960s, the social democratic government officially abandoned the project of designing Swedish nuclear weapons and the Marviken plant became derelict. It was never loaded with fuel, and the project was cancelled in 1970.
The situation that the reactor was nearly completed, but never loaded with fuel, made it possible to use the plant for advanced international experiments during late 1970:s and early 1980:s, simulating various aspects of accident scenarios in nuclear power plants. Four series of experiments were performed:
When the construction of the nuclear reactor was finally stopped 1970 a boiler house and an oil fired steam boiler was built. This made it possible to use the non-nuclear parts of the power station as well as the connecting power grid line. Since the turbine was optimized for the comparably low steam temperature and pressure from a nuclear reactor the efficiency of the oil fired plant became low (approximately 30 percent) compared to conventional fossile fired plants which may have efficiencies of 40 or even close to 50 percent. Hence the plant was only used as a peak load plant.
The oil fired boiler had a thermal power of approximately 700 MW at an oil consumption of 17 kg/s, and the corresponding electrical power was approximately 200 MW. The plant was in operation until March 2009, but has since been decommissioned.
The Nuclear reactor, the oil fired power station and surrounding 250 hectares of land and water was acquired by Synthesis Real Estate during 2018. Synthesis Analytics is building a computing center to leverage the vast access to energy[further explanation needed] while Synthesis Real Estate will develop an Archipelago City heated by the surplus heat from the computing center.
The nuclear reactor at Marviken plays a big role in Swedish thriller/sci-fi writer Lars Wilderäng's 2020 novel Redovisningsavdelning Marviken (Swedish: "Accounting Department Marviken").