Leaders, scientists and policymakers know that innovation will be key in reducing carbon emissions. Bill Gates is betting on it. His high-tech start-up company TerraPower LLC is designing a new nuclear reactor connected to a massive, cheap energy storage tank that, when combined with intermittent wind and solar generation, will provide the reliable electricity around the clock that is essential to a carbon-free future.

The system, Natrium, was co-developed by TerraPower and GE Hitachi Nuclear Energy, and thanks to the U.S. Department of Energy, it just got a big push towards deployment. Innovation in carbon-free energy will define the 2020s and Natrium is one of the advanced reactor designs leading the way.

Natrium Combines a Reactor With Thermal Energy Storage

The Natrium design was one of two concepts selected by DOE's Advanced Reactor Demonstration Program for extensive funding. It is an advanced, high-temperature nuclear reactor, hooked up to a giant tank filled with molten salt to store energy.

In today's nuclear plants, the reactor heats up water into steam which turns a turbine to generate electricity. In the Natrium system, all the reactor's energy is delivered to the tank as heat instead. The equipment that turns heat into steam and then electricity is connected to the other side of the tank. As a result, the reactor can run uninterrupted 24/7 regardless of demand and operators can use the stored heat to make electricity as customer demand requires.

Moving the steam generators, turbine and electric generator away from the reactor also allows those systems to be made from standard, commercial off-the-shelf components, which are less expensive than nuclear-grade equipment. And Natrium won't be disturbed by glitches on the grid or in the generator, which today can make a reactor go offline.

In addition, the reactor would operate at higher temperatures than the ones now in common use. The Natrium proposal builds on years of work by GE Hitachi on the PRISM reactor and by TerraPower on the Traveling Wave Reactor. Natrium runs at much lower pressure than today's pressurized water reactors. Lower pressure also makes construction easier and less expensive.

Thermal Storage Is a Heat Battery

Connecting a reactor to a thermal storage system instead of directly to an electric generator lets the reactor smooth out the grid's total production. The reactor runs steadily, no matter what the weather conditions, and a huge, inexpensive energy storage system (in this case a heat tank) is charged when there is a lot of wind or solar, and discharged when there isn't. Heat is the cheapest way to store energy, and reactors are an excellent way to make carbon-free heat.

The thermal storage concept isn't unique to the Natrium partners. Dozens of engineers from around the world participated in a recent engineering workshop to discuss the applications of thermal storage. The storage medium could be molten metal, or salt, or something as simple as a big pile of rocks or concrete.

This Innovative Design Helps Wind, Solar and Nuclear Work Together

Storage allows the plant to rapidly change its electric output from approximately 100 megawatts to 500 megawatts without the reactor needing to change power. Such a system would allow zero-carbon energy from solar farms to power the grid during the day, while the reactor stores energy in the tank. In the late afternoon, when demand reaches a peak and solar generation declines, heat from the tank can be tapped faster than the reactor is adding it. Likewise, Natrium could create space on the grid for electricity made by strong night-time winds by storing the reactor's output, but could still assure adequate electricity in the morning.

Wind and solar will be an important part of a carbon-free energy system but they cannot do it alone, as researchers at the Massachusetts Institute of Technology have illustrated. Using reliable nuclear energy, Natrium is designed to fill this need. TerraPower's and GE Hitachi's Natrium reactor is "designed to provide firm, flexible power that seamlessly integrates into power grids with high penetrations of renewables."

The Natrium System Will Enable a Carbon-Free Future

The Natrium system shows the kind of new thinking that will be needed for the transformation that we urgently need in the next couple of decades. It will take more than just adding carbon-free sources; it will also take adding equipment that can knit the system together. TerraPower's and GE Hitachi's design is ensuring that our carbon-free future is also one with reliable electricity.

"TerraPower's work on Natrium is phenomenal in terms of developing low-cost, large-scale energy technology that will meet the rising energy demand while reducing greenhouse gas emissions," said Gates.

This article is reproduced at electricenergyonline.com