Science In Real Life

The word nuclear has come a long way. From humble beginnings as a Welsh root meaning “nut”, up through a general sense of a center point around which things cluster, acquiring a biological meaning as regards cell structure, it has lately come to refer, at least in connotation, to what is undeniably the most potent pack of processes ever produced by physicists. As we wrap up this series on power, we must finally come to grips with the most powerful source known to mankind. We shall see that even solar power, that unstoppable juggernaut of free energy, is at heart a nuclear source.

Some of you may indeed remember that from all the way back at the Sun essay. The immense gravity of that roiling ball of hydrogen gas is sufficient to cause nuclear fusion at its core. Someday fusion may be a viable power source, and I will briefly address the main approaches later. But first, fission. Fission is the operative mechanism in all nuclear power plants in use today. Using it to produce electricity requires careful and precise control of a very violent process, so naturally we turn to sports fans for a suitable analogy.

Imagine a hypothetical city containing Yankees fans, Eagles fans, and Red Sox fans. The Yankees and Eagles fans, on their shared game night, are distributed in more or less equal numbers throughout the city’s numerous sports bars, each of which represents the nucleus of a uranium-235 atom. The Red Sox fans, representing the electrons in this analogy, are just as numerous as Yankees fans but have far less influence. They cannot get into the bars and are constantly driving around them in circles; we will say no more about them. Now, inside each bar is a delicate balance. The Yankees fans, being far more boisterous than their football counterparts, need a certain number of Eagles fans present to dilute their enthusiasm. On the other hand, too many Eagles fans and the uniformity has everyone thinking they should just go watch the game at home.

So now I start sending more Eagles fans into the city. Here is where a wonderful thing happens – if an Eagles fan of just the right fervor enters one of these bars, the reshuffling that ensues leads everyone to decide that it would be easier to split into two separate, smaller bars. Poof! It is done. In addition, to maintain the balance in the two smaller bars, several highly energized Eagles fans head out into the night to find other bars. They are going too fast, but their speed is moderated by the ever vigilant Hypothetical City Police Department, so when they each enter another bar, the process repeats. Thus we have a chain reaction that releases immense amounts of energy. In an actual nuclear reaction, this energy manifests mostly as heat, from the motion of the splitting nuclei, and radiation, from various side effects of the fission.

I mentioned the HCPD moderating the free neutrons. There are many types of nuclear reactors, and depending on how the uranium fuel is used, it is often desirable to slow down the neutrons released in each fission. This may be done with regular water, heavy water, or graphite. In all nuclear reactors, coolant (frequently the same substance as the moderator) is used as both a safety mechanism and an energy extractor. The coolant is heated by the nuclear fuel and used to spin the turbine of an electrical generator. By removing the heat from inside the reactor core as quickly as it is produced, we make sure the self-sustaining nuclear reaction does not attempt to re-enact the battle of Trafalgar. A nuclear bomb is, very simply, a small contained fission reactor with no cooling mechanism. This fact, unfortunately made manifest in several meltdowns, has generated an atmosphere of extreme caution regarding the use of nuclear power.

Nowhere is this more the case than in the United States, where a confluence of factors in the 1970s resulted in a massive drop in construction of new plants. Meanwhile new designs have been tested and implemented elsewhere, resulting in a new generation of inherently safer plants, with an emphasis on reactor designs that will safely shut down even without operator intervention. Other concerns include long-term storage of the highly radioactive waste and proliferation of fissionable material. These problems would be avoided with a viable fusion reactor, which produces neither.

Achieving a fusion reaction hinges on just one thing: compression. Take ordinary matter, get it hot enough and small enough, and fusion will happen, releasing tremendous amounts of heat and light. On a scale of 1 to difficult, this rates a solid “camel through the eye of a needle.” The tokamak and Z-pinch machines make the attempt by confining the super-hot fourth state of matter known as plasma with magnetic fields, much like trying to herd cats with tennis rackets. Another approach, laser inertial confinement, compresses a pellet of fuel with lasers from all sides until it gives in to peer pressure and explodes. Much progress has been made, but there is a long way to go until commercially feasible plants can be designed.

And so we reach the end of the Science in Real Life series on power. Hopefully I have managed to plant a better understanding of the current methods for keeping our civilization going full steam ahead.