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TerraPower’s ultimate energy recycling project

spent nuclear fuel rods
Spent fuel rods in storage could be a future
clean-energy fuel. - credit: SRNL

Robert Millikan, born March 22, 1868, was an American experimental physicist and Nobel laureate. His work laid some of the foundation for modern particle physics, and few scientists of his time had more expertise and understanding of elements of the atom. In 1928 at the New York Chemists’ Club, Millikan declared: “There is no likelihood man can ever tap the power of the atom. The glib supposition of utilizing atomic energy when our coal has run out is a completely unscientific utopian dream, a childish bug-a-boo.” Sometimes the experts can fail to realize what’s possible.

Today there are also some experts who consider the idea of a traveling wave reactor to be a type of “utopian dream.” I suspect they may also be wrong. Scientists and engineers at TerraPower have a firm belief that the spirit of invention can break through the barriers of preconceived notions. One of their projects is a traveling wave reactor design that can generate emission-free electricity for decades on a single cylinder of fuel. Better yet is this cylinder can be made up of the existing waste fuel from conventional nuclear reactors that’s been problematic to store.

World energy demand will almost certainly increase into the foreseeable future. Harnessing wind and solar is a no-brainer, but they have limitations and don’t do 24/7 very well. A continuous generating system that can be self-sufficient for decades by recycling a waste product has to be considered as a solution to a difficult energy problem.

John Gilleland is the CEO and Nuclear Program Manager of TerraPower, an enterprise at the forefront of this technology. They have some bold ideas, and serious plans to make them a reality. Following is our Q&A exchange on some questions I had about the project.

Q. You’re investing in a type of nuclear reactor called a 'Traveling Wave Reactor'. That has a sort of Star Trek-like sound to it but it’s actually simpler and more straightforward than it seems to suggest. Can you describe the traveling wave concept and how it originated?

A. A TWR needs enriched uranium start up. Once started up, the TWR is envisioned to sustain fission given only non-fissile (i.e., fertile) fuel such as depleted uranium, a waste product from the enrichment process used for present light water reactors. In one manifestation, the TWR sets up a slow-moving wave in which neutrons produced by fission in the critical part of the core convert adjacent fuel from fertile isotopes (such as U238) into fissile isotopes (such as Pu239).

The traveling wave can move, the fuel can move through a fixed wave or some combination of the two. Also, the wave can be in a long rectangular region moving along the axis, or at the center of a cylinder, with fuel moving into and out of the quasi-static central reaction region. Our current engineering is pointing towards this latter arrangement for a variety of reasons.

Precursors to traveling wave reactors (TWRs) were first proposed in the 1950s and have been studied intermittently since. Today, we have improved computer tools for extensive simulations and 3-D modeling. We can do analysis that has never been possible before that will make the concept a reality.

Q. The reaction that moves across the fuel cylinder, is this a classic fast breeder type reaction or a variation of it?

A. No. The TWR introduces a new class of fast reactors. We have integrated classic fast reactor engineering into a design that includes an innovative core and unique physics that haven’t been used before. By moving the fuel through a quasi-static power-producing region in carefully planned ways, the fertile material is converted to fissile fuel. Classic breeder reactors rely upon the periodic removal, reprocessing, and re-insertion of fissile material. We eliminate the need for reprocessing classic breeder reactors require.

Q. Breeder reactors, that turn non-fissionable material into fissionable fuel as they operate, have been tested and operating for decades. Your traveling wave reactor is still limited to computer modeling. Is that correct?

A. 21st-century computer modeling has allowed TerraPower to make advancements in the study of fission chain reactions using depleted uranium as fuel, building upon the previous five decades of research.

Q. What seems to be the toughest challenge of the concept?

A. Right now, we’re working on developing and testing materials that will withstand high radiation exposures so the reactor core components and fixtures can last as long as the fuel.

Q. Is there a time frame for building and testing a prototype reactor?

A. TerraPower plans to build a 500 MW (electric) demonstration reactor by 2020.

Q. I’ve heard you may need to conduct the initial physical tests outside the US. Is that because of regulatory restrictions?

A. No. The main reason is that the facilities to perform the necessary research are not available in the United States at this time. Other countries, such as Russia, India and China, already have key facilities in place. Obviously, we’d like to run our tests in the U.S., but it’s just not feasible at the moment. It’s much easier to run tests using existing technology rather than construct it from the ground up.

Q. Is overcoming public adversity to new nuclear energy projects nearly as difficult as the physics itself or is the perception problem starting to fade?

A. We have not encountered public adversity to this concept. In fact, our experience is that the public is very interested in carbon-free sources of energy, and our reactors certainly fit that description. And, according to trade journals, the public’s perception of nuclear energy is positive and growing.

Q. Assuming the computational physics all works out, and you successfully build and test a prototype, what do you imagine as the first real application?

A. We call it a demonstration reactor rather than a prototype because it will be generating a substantial amount of electricity in addition to serving as a research reactor.

Q. Does the design lend itself better to larger or smaller reactors, or is it simply a matter of manufacturing the fuel cylinder to fit the application?

A. It doesn’t necessarily lend itself better to one or the other. The Department of Energy definition for a small reactor is a reactor that produces 300 MW (electric) or lower. Our plans call for a 500 MW (electric) demonstration reactor. We also have plans for a 1,000 MW (electric) reactor.

Q. Are there any other energy projects you might be working on that you’d like to share?

A. Right now, TerraPower is focused on bringing the traveling wave reactor to market. We’re planning on the demonstration reactor being operation in 2020.

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