Wednesday, February 17, 2010

Traveling Wave Nuclear Reactors

by Richard Crews
Have you heard of "traveling wave" nuclear reactors?

Unlike the current reactor design that uses only enriched uranium for fuel, the traveling wave design largely uses waste byproducts of that enrichment process, that is, "waste" uranium.

A small amount of enriched uranium is used at the beginning of the process but then the nuclear reactor runs on the waste products and can make and consume its own fuel. The benefits are that the reactor doesn’t have to be refueled or have its waste removed until the end of life of the reactor (theoretically a couple hundred years). Using uranium wastes reduces the amount of waste in the overall nuclear life cycle, and extends the available supply of the world’s uranium for nuclear reactors by many times.

The leading company developing this technology is TerraPower, financed and championed by Bill Gates. The process depends on modern supercomputers. According to the Website of Intellectual Ventures, a spin-off from Gates' Microsoft:

"Extensive computer simulations and engineering studies have produced new evidence that a wave of fission moving slowly through a fuel core can generate a billion watts of electricity continuously for well over 50 years without enrichment or reprocessing. These results are made possible by advanced computational abilities of modern supercomputer clusters, the driving force behind one of the most promising nuclear reactor design efforts in the country."

How close to real-world use is this technology? According to experts, operation of a traveling wave reactor can be demonstrated in less than ten years, and commercial deployment can begin in less than fifteen years. The main difficulty is that significant materials advances would be required to create a cladding, or cover, for the core that could contain a fission reaction for decades.

I wonder why one can't just start with a tough, 6-foot thick ceramic layer, and then layer more ceramic on the outside of that as it vaporizes from the bottom and inside through the years. Maybe if the ceramic's residue degrades and collapses, it contaminates the core and disturbs the balance of the ongoing reaction (although the composition of the core is evidently not critically precise--and anyway adjusting to that is the giant computer's job).

Or make the core cone shaped (instead of cylindrical) so as it ages, it sinks to a smaller and smaller working diameter.

Take a look at an article in Scientific American for a more extensive discussion of the economic and technical problems of Traveling-Wave and other nuclear power technologies.