Ever wonder how a nuclear reactor works? We’ve heard of fission and we know that electrons surround a nucleus. But what do these things mean? Perhaps you think something causes electrons to get chemically angry and just leave their nuclear family. Maybe you think that some divine magical force is holding all those atomic particles together until one loses it’s job from a drinking problem and fission occurs. Or you never thought about nuclear beyond its causing three heads, super powers, and the dreaded kaiju?
That’s okay, because we’re about to dive in and find out just what is really going on. If you’re certain the nuclear monster is evil, you just might be a little disappointed. But you’ll be ahead of what millions of people don’t know.
Believe it or not, the design of electricity generating nuclear reactors is to—just get hot. Not very hot. An efficient, always-on hot. Even the top heat of the hottest fission reactors can’t melt glass. Recently, I melted glass in a campfire. It was fun to watch it liquefy like molten lava. I suddenly realized that my campfire was hotter than a nuclear reactor!
All those hot wing sauce advertisers—they’re wrong! They ought to change the level of hotness on their menus. It’s deceiving! “Nuclear” should be above “Hot” but below “Campfire” and definitely way lower than “Meeting the Future In-laws”! “Nuclear Fusion” is supra-Armageddon hot. But that’s another story and besides, no one can seem to get that working—yet.
You can think of a nuclear reactor kind of like a campfire minus the electricity production. But similar to placing a kettle of water on a campfire, a boiling water reactor (BWR) or a pressurized water reactor (PWR) heats up the water—called the transfer medium—to produce steam. The steam spins a turbine that drives an electromagnet that produces an electric current much like the alternator in your car.
There are even some reactors that don’t use water as the transfer medium. One example is the liquid fluoride thorium reactor (LFTR) that runs very hot. This and other newer designs being blocked from development mostly due to politics, are more efficient and inherently safer because water is not a very good transfer medium at hotter temperatures. So really we can see an operating nuclear power machine is like a campfire boiling a kettle of water. There are all manner of nuclear reactors out there. But they all work in this same elementary way. All use water but soon some will use compressed carbon dioxide. But they all heat up a transfer medium to power a turboelectric generator.
“Wait! . . . So a nuclear reactor is just a glorified steam engine?”
“Well yes. Yes, it is.”
So why do we bother moving a turbine in this way? There is this thing called energy density and it makes nuclear energy a very interesting and appealing approach to supplying power. Energy density is loosely defined as “the amount of energy something gives off for a given amount of substance.”
For example, a solar panel. Our Sun at ninety-three million miles away gives off enough energy to burn up a thousand planet Earths. A tiny ray of solar energy makes it to a neighbor’s roof only capable of powering his electric toothbrush because his crud-covered panels haven’t been cleaned in a year and he’s running at trickle level. Another hermit geek neighbor, who is scary weird and said to have an odd cylinder in his basement that looks like a scuba tank hooked to his fake power service—an unlicensed plutonium-238 radio-thermal generator (RTG) that’s been running his and a few other houses (you don’t want to know) for the past twenty years and still going! Solar is diffuse—not energy dense—and plutonium-238 is very energy dense.
At least 2.5 billion sometimes-on solar panels over millions of square miles would be needed to replace present US nuclear power production that sits on acres—and an immense amount of carbon energy to make and install those billions of solar panels! Our current US fleet of 99 nuclear reactors supplies 20% of always-on nonemitting electricity demand. Solar at Earth surface is not energy dense and nuclear is very energy dense.
Einstein gave us his famous E = mc2 energy-mass relationship, where E is the rest energy, m is the rest mass, and c is the speed of light. The coolest part of this simple looking equation is the equals sign. It says, by definition, that they are the same. Not almost the same but totally, completely, and exactly the same. It’s common and very useful to see rest mass—or stuff—expressed in terms of its rest energy, which can in turn be thought of as the total energy all tied up in doing things like holding the atomic and subatomic world together. It’s impossible to access all of it, but in a moment you can see just how much energy is hanging out in there.
A cup of water will be our example to help illustrate rest energy and the idea of energy density. We may use the relationship above to calculate that a single cup of water has 1029 MeV of rest energy. (The MeV is the mega-electron volt explained at Neutrons: “What Are They?”)
So. What is 1029 MeV? The rest energy of a cup of water is a number with twenty-nine zeroes—stupefying. Beyond huge. Water is stuff or mass and Einstein showed that mass has a ginormous amount of energy. Still, it’s hard to imagine. To help get a picture of the sheer immensity of this nuclear power, one cup of room temperature water just sitting there has enough rest energy to supply for six months the entire world’s energy demand of more than 15 trillion watts!—well, if it could be unleashed. Let that sink in. One cup of water. Six months of a world of energy. Well, yes. Yes it can.
Water is vital for life. It has two hydrogen atoms and one oxygen per molecule. The element that powers the core of a nuclear reactor by fission is the infamous uranium. The latent chemical energy in water is a million times less energy than the nuclear energy of uranium. Water is much less energy dense than nuclear fuel but only in terms of chemical energy.
Nature provides one other nuclear fuel that has gone unnoticed in the main for too long. Thorium. Only one nuclear reactor in the US fleet ever used thorium back in the 1970s. In a LFTR, it provides more than dense power. Thorium in a LFTR produces isotopes for nuclear medicine and new emerging radio therapies that are very much in their infancy because the isotopes are so rare. For example, targeted alpha therapy has the potential to cure some types of lymphoma if only the isotopes required could be accessed before they decayed away. But the sad state of politics, poor public perceptions of nuclear anything, and fear of science stand in the way of cures for cancers. Take heart. It’s a brand nuclear day. Perfect for fission!
And those big scary towers by nuclear power plants located by bodies of water? Those imposing ominously shaped structures emitting white clouds of frighteningly suspicious vapor? Those are water cooling towers to remove the generator heat so the plant can work! It’s just water vapor, folks. And it’s absolutely not radioactive above the natural background radiation we’re all bathed in every day. And definitely not a greenhouse gas. Feel free to relax!
“. . . almost everything is already discovered, and all that remains is to fill a few insignificant gaps.”
—1878 when Professor Jolly was advising his student, Max Planck, to not pursue theoretical physics. Planck ignored his teacher’s advice and forever changed the human understanding of the natural world when he discovered the energy-time Planck constant that created the field of quantum mechanics so we could have cell phones.
“In 1905, when Einstein . . . sent five revolutionary papers to the physics journal that Planck edited in Berlin, Planck immediately recognized them as works of genius and published them quickly without sending them to referees.”
—Freeman Dyson in The New York Review of Books, 2015. Einstein’s E = mc2 was in one of those papers.
Does your new understanding of energy density affect your opinion on solar and wind energy? Did you know that nuclear power is one of the top clean energy sources for electricity? Or that nuclear power is the safest industry in the world? Would you like to read more about rest energy and relativistic physics? Please leave any comments and feedback below. Until next time . . .