Readers of this blog are familiar with the potential nuclear proliferation problems of both uranium reactors and plutonium reactors. As a quick summary, natural uranium is mostly an isotope called U238 which cannot sustain a chain reaction nor make a bomb. To make a uranium reactor you need to "enrich" the uranium, that is, remove some of the U238 so that the concentration of U235, the uranium that works in reactors (and bombs) is increased. The problem is that the same technology that can be used to make nuclear fuel can also make nuclear bombs. (Iran is doing this now.)
Another fuel for bombs is Plutonium239, which can be produced in a standard nuclear reactor, and then separated out chemically from the uranium and other materials in the fuel. It is easier to make P239 in a reactor than to separate U235 from natural uranium, but it is harder to make a working bomb. (North Korea is taking this approach.)
P239 makes a good fuel for power generation, and it can be produced from U238, the non-fuel isotope of uranium.
Imagine a cigar made from moist tobacco leaves. The leaves will not burn unless they are dried first. If you light one end of the cigar with a match, the heat of the burning leaves will dry the unburned leaves and ignite them as the cigar burns from one end to the other, leaving ash behind.
A newly proposed powerplant design called a "traveling wave reactor" works like a nuclear cigar. The cigar is a tube of unenriched uranium, mostly U238. A little U235 acts as a match at one end to produce neutrons that will change the U238 to U239, which decays in two steps, first to neptunium and then to plutonium. The plutonium acts as a fuel for the reactor and produces power and more neutrons that continue the process of producing new fuel from the inert U238 down the tube. The reaction, like the glowing tip of the cigar, travels down the tube over time, leaving reaction products (spent fuel), behind and producing more fuel from the unenriched uranium. This is the "traveling wave" reaction.
This reactor, once started, does not produce easily accessible plutonium that can be diverted to bomb making (it is very easy to tell if an operating reactor has been shut down, and if the nuclear cigar is shut down it indicates either an operational problem or a potential plutonium diversion.) Also, the reactor only needs a small amount of enriched uranium to act as a match. All the enriched uranium required for every reactor in the world could come from one enrichment facility.
Finally, the reactor, once started, would burn all its fuel over a period of 50 years or so, meaning no re-fueling "outages" a great cost item to nuclear reactors. Also, the nuclear waste stays in the reactor, eliminating the need for short term storage of spent fuel over the life time of the reactor.
Nuclear power is our best possible option for clean, inexpensive energy to power the economic growth for future generations, and the nuclear cigar is one possible way to make it safe and simple.
The nuclear cigar:
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