A steam turbine that drives a generator is usually only about 30% efficient. Based on the Brayton-cycle system, developed by George Brayton more than 100 years ago, an air or steam system heats the air or water in a confined space and then releases the compressed air or steam to turn a turbine generator.
The Brayton-cycle is the same principle used in a jet engine, which burns fuel to run a turbine and then shoots the compressed air out the back to thrust a plane forward. It’s a common system.
Sandia National Laboratories has developed a turbine system that could substantially improve energy efficiency in small modular nuclear reactors. The Lab is already seeking an industry partner to market the technology.
Gary Rochau, manager of the advanced nuclear concepts group at Sandia’s Nuclear Energy and Fuel Cycle Technologies Center said the new turbine system uses carbon dioxide in a closed-loop variety of the Brayton-cycle turbine to crank up electric conversion from heat.
Rochau explains the Sandia design closes the system so the carbon dioxide circles back for reheating and recompression in a continuous closed loop. Its not a new idea, but using “supercritical carbon dioxide” is, and that’s what adds efficiency. Supercritical CO2 is the point where heated and compressed carbon dioxide reaches an unusually dense state, between a gas and liquid. In that state, the released CO2 converts a lot more heat to electricity than air or steam turbines.
An enthused Rochau said, “It works great for energy conversion to get a much higher level [of electricity] from an energy heat source. A supercritical CO2 Brayton-cycle system can reach 50% conversion efficiency.”
The system is also much less expensive to build because it’s very compact. Because of its size, it wouldn’t pair up in large power plants like coal-fired generators. But it’s well suited for tiny plants, such as small modular nuclear reactors (SMR).
SMRs are the newest generation of nuclear reactors and should be an alternative to today’s mega plants, which produce 1,500 megawatts or more of electricity and cost up to $10 billion to build. The SMR prototypes range from as low as 10 or 20 MW to 300 MW.
Jeff Hamel, program manager at the Electric Power Research Institute notes at that size, nuclear could become an option for the first time to small- and medium-sized power companies.
The National Labs are already deep into the SMR effort. Los Alamos National Laboratory has licensed technology to Gen4 Energy Inc. (formerly Hyperion Power Generation Inc.), to build a 25 MW mini-reactor. Gen4 has a cooperative research and development agreement with LANL to help build its first prototype. Plus Gen4 has a memorandum of understanding with the Savannah River National Laboratory to put its first demonstration pilot plant at the Savannah River site.
The U.S. Department of Energy announced a few months back it would provide $452 million for a cost-share program to help develop SMRs. The Federal funds would help SMR developers work toward licensing from the Nuclear Regulatory Commission. It’s a classic case of government working at cross-purposes at taxpayer expense.
Rochau is upbeat because the Sandia turbine technology is applicable to SMRs. There are also nondisclosure agreements signed, but no cash yet.
Generation plants are a big investment. Demand alone doesn’t get new plants built. There are regulations from local to Federal, fuel cost considerations, capital return matters and an avalanche of other considerations to be reconciled before an energy supplier can sign on.
But SMRs offer an intense, low cost and low fuel cost solution to a much larger group of smaller utilities. Sandia’s new generator offers something quite useful, going from 100% power to 166% power. Two thirds more ability to earn revenue has quite an effect.