Thursday, June 3, 2010

Technology: Traveling Wave Reactors

TORONTO, ONTARIO - Earlier this year, this blog featured the thorium reactor as a potential alternative for improved nuclear power in the future. While no "expose"-type publication has come out, the quiet consensus from nuclear professionals expressed in letters to the editor is that the promise of the thorium reactor as a panacea for the recognized issues with nuclear technology is oversold. It might be modestly harder to get nuclear weapons fuel from a thorium reactor, but it's still possible, and the other purported savings in waste are not especially significant, and the higher abundance of thorium is not especially relevant when breeder reactors can make enough of their own fuel for any degree of anticipated demand yet forecast.

Instead, an older article in Technology Review magazine touts the traveling wave reactor as a much more likely way to move nuclear energy forward toward a less expensive and and safer future. Also boasting its own Wikipedia page, the traveling wave reactor differs from current nuclear plants in that it does not require enriched uranium, and the fission reaction occurs in a specific moving zone (hence the name "traveling wave") instead of through the entire core of the reactor.

The traveling wave reactor isn't a panacea, either. It probably requires about 10% enriched uranium (U-235) to start a fission reaction. However, once the chain reaction is started, it can be sustained with depleted uranium (U-238), and most theoreticians believe that a single fueling could quite possibly last 60 years or more, contrasted with 2-3 years using conventional technology. Right there, proliferation concerns would be diminished, as there would be no materials being removed from the reactor that could be diverted, and since the fuel is no longer (mostly) enriched, there is a lesser need for materials that could be diverted.

Another potential issue is that the reactor would have to be cooled by liquid sodium and operate at 550 C, instead of the 330 C typical of current reactors. However, that doesn't automatically mean lower safety; assuming proper reactor design and cooling systems the danger might not be significantly different.

To this point, most of the work on traveling wave reactors has been at the behest of venture capital firm Intellectual Ventures. Unlike the thorium advocates, they don't view it as a short-term technology, but one that may take hold if an expansion of nuclear power takes place in the United States, what it calls a "nuclear renaissance."

Somehow, I suspect nuclear critics would find a different word than "renaissance," and it will take a lot more than an oil spill to push the world toward traveling wave reactors.

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