Advanced Traveling Wave Reactors

Traveling-wave reactors offer a new class of nuclear plants that could avoid some of the drawbacks that have prevented nuclear energy from reaching its full potential as a sustainable, carbon-free source of electricity and heat. Nuclear energy has an impeccable safety record in recent decades and is as reliable as power plants come. Concerns about the proliferation of uranium enrichment technology are high and increasing, however. And no one is happy with today’s solutions for nuclear waste.

Traveling-wave reactors offer a path to zero-emissions energy that greatly lowers proliferation risks and that could reduce nuclear waste volumes, buying time to set up a long-term solution. Exploiting new physics that has only recently been fully explored with 21^st-century computational tools, traveling-wave reactors run on depleted uranium, a waste byproduct of the enrichment process. Huge amounts of depleted uranium already exist in stockpiles around the world, with more being made each year as the fleet of conventional reactors is refueled. Burned in traveling-wave reactors, this inexpensive but energy-rich fuel source could provide a global electricity supply that is, for all practical purposes, inexhaustible.

A traveling-wave reactor can sustain fission in a nonfissile fuel such as depleted uranium because it sets up a slow-moving wave in which neutrons produced by fission reactions in one small part of the core convert adjacent fuel pellets from fertile isotopes (such as U²³⁸) into fissile isotopes (such as Pu²³⁹). In other words, a TWR breeds its own nuclear fuel, where it needs it, when it needs it. Exhausted fuel can be left in the core. So unlike conventional nuclear plants that take in new fuel and expel high-level waste every 18 months or so, a TWR can in principle be fueled once, sealed up, and run without refueling for 60 years or more.

A relatively small amount of highly active material is needed to get the wave going in a TWR. Enriched uranium, plutonium recovered from disassembled nuclear weapons, or even exhausted fuel from existing TWRs could serve as the starter fuel. In the long run, TWRs require so little fissile fuel—and are so flexible in accepting various kinds of starter fuel—that they could form the basis of a civilian nuclear technology that could be built and deployed widely throughout the world without setting up any new enrichment plants. The technology thus offers, at last, a way to resolve the tension between the need for clean, safe, and sustainable electricity from nuclear power and the need to prevent the proliferation of nuclear weapons technology.