The Supercritical CO2 Turbine: Waterless Wonder

TL;DR

Supercritical CO2 turbines can be 10 times smaller than steam turbines and match their efficiency at lower temperatures, making them promising for nuclear and waste-heat applications.

Key Points

• 1.Supercritical CO2 turbines can be roughly 10 times smaller than equivalent steam turbines. When CO2 is supercritical, its fluid density is 50% higher than steam, allowing far smaller components and fewer stages while maintaining competitive thermal efficiencies of 48–50%.
• 2.CO2 reaches its critical pressure at just 7.38 megapascals, about a third of water's critical pressure. Near this limit, CO2 becomes more incompressible and liquid-like, reducing the energy cost of compression — a major advantage over helium Brayton systems.
• 3.The concept dates to 1948 when Swiss firm Sulzer Brothers filed the first patent, but Ernest Feher's 1960s papers at Douglas Aircraft defined the modern supercritical power cycle. Soviet engineers Gokhshtein and Verkhivker and Italy's Angelino independently confirmed efficiency advantages in the same era.
• 4.Interest collapsed in the 1970s because light water reactors only reached 200–300°C, well below the turbine's ideal 550°C inlet temperature. The technology was revived in the 2000s when Generation IV reactors (molten salt, very high temperature) and Small Modular Reactors matched that sweet spot.
• 5.Major technical challenges include seal failures causing windage losses up to 2% efficiency, and poorly understood material degradation. CO2 causes carburization, sensitization, and high-temperature corrosion in stainless steel and nickel alloys over a 30-year operational lifetime.
• 6.The US STEP project (10-MWe Supercritical Transformational Electric Power) completed Phase 1 testing in late 2024, generating electricity for the first time. Startups like Echogen (partnered with GE Vernova), NET Power (Allam cycle), and Arbor Energy ($55M Series A) are pursuing commercial applications.
• 7.China opened what it called the first commercial supercritical CO2 power generator at a steel plant (Chaotan One) in December 2025. European projects include CO2OLHEAT harvesting waste heat from a Czech cement plant and SOLARSCO2OL integrating the turbine with solar thermal power systems.