Stochastic Scribbles
Random musings in a variety of subjects, from science to religion.

Fusion supporting fission

Practical power generation with controlled fusion is one of those things that has always been “just thirty years away”, in contrast to uncontrolled fusion that goes boom from over fifty years ago. But it turns out that controlled fusion does not even have to reach its breakeven point, where more power is generated by fusion than is consumed, to be useful as researchers at the University of Texas at Austin have devised a way to use fusion to reduce nuclear waste.

While atoms such as uranium or plutonium can break apart all by themselves, they’re much more likely to split apart when hit by a neutron. Fission in nuclear bombs or nuclear reactors takes advantage of neutrons emitted from splitting atoms, where a dense enough blob of fissionable elements will cause a chain reaction and generate a lot of energy. In fact, one of the issues in nuclear reactors is to keep the neutron emissions low enough lest a meltdown occurs. But nuclear fuel in nuclear reactors eventually reach the point that they are no longer useful for generating energy, as not enough neutrons are emitted to split the still plentiful fissionable atoms. Even worse, the fissionable atoms make nuclear waste radioactive.

What the researchers from the University of Texas at Austin did was to devise a way to use fusion to promote fission. Using a room-sized tokamak, neutrons are emitted from the fusion reaction in the tokamak. These neutrons bombard nuclear waste and promote fission in the material. Not only does this generate energy from the nuclear waste, it also turns much of the fissionable atoms into non-fissionable ones, which greatly reduces the amount of radioactive nuclear waste. The researchers have yet to build an actual system for reducing nuclear waste, though, so it still remains to be seen whether there will be an unforeseen caveat that renders their method impractical.

This method of reducing nuclear waste and generating energy is an interesting reversal of the relationship between fusion and fission in thermonuclear warheads, which use fission to cause a fusion reaction. On the other hand, they aren’t so different after all as both end up using neutrons from fusion to enhance fission, since most thermonuclear weapons use the fission-triggered fusion only to force more fission to occur.