Generation IV (Gen IV) refers to a class of advanced nuclear reactor designs identified by the Generation IV International Forum (GIF), a multinational research initiative founded in 2001. The forum selected six reactor concepts — sodium-cooled fast reactor, lead-cooled fast reactor, gas-cooled fast reactor, molten salt reactor, supercritical water-cooled reactor, and very high temperature reactor — as the most promising paths toward next-generation nuclear energy with step-change improvements over existing reactors.
Gen IV designs aim to address the limitations of today's Generation II and III reactors. Key objectives include enhanced passive safety (reactors that shut themselves down and cool without operator action or external power), much higher operating temperatures enabling industrial process heat and hydrogen production, closed fuel cycles that dramatically reduce long-lived waste, and improved resistance to nuclear proliferation. Many SMR designs under development are based on Gen IV concepts, making the two categories closely intertwined.
The transition from Gen III to Gen IV represents a fundamental shift in nuclear reactor philosophy — from designs that rely on engineered safety systems and operator intervention to designs with inherent and passive safety features. Companies like TerraPower, Kairos Power, X-energy, and Newcleo are bringing Gen IV concepts toward commercial deployment. While none has yet reached full commercial operation in Western countries, several demonstration reactors are under construction or in advanced licensing stages, with first operations expected before 2030. For deeper coverage, see DeepTechIntel's nuclear section.