A small modular reactor (SMR) system that uses a supercritical carbon dioxide (CO₂) Brayton cycle instead of the steam Rankine cycle is under development at the Korea Advanced Institute of Science and Technology (KAIST).

The 12-MW Micro-Modular Reactor (MMR) concept proposed by a research team led by professors Jeong Ik Lee, Yonghee Kim, and Yong Hoon Jeong could be transported by truck and is well suited to remote areas. It uniquely uses supercritical CO₂ as a coolant as well as a working fluid, and it can run without refueling for 20 years and maintain decay heat removal by natural circulation. Additionally, it uses a next-generation printed circuit heat exchanger with no joints, welds, or points of failure, and is small and light because it adopts the semiconductor manufacturing process, the researchers said.

The system (Figure 4) integrates the supercritical CO₂ Brayton cycle to keep the reactor compact, the researchers said. Supercritical CO₂ is an innovative power generation cycle whose turbomachines are smaller than those of the steam cycle or helium cycle, they noted. Meanwhile, a supercritical CO₂ cycle achieves comparable efficiency with the helium Brayton cycle, but with a much lower turbine inlet temperature (550C versus 850C).