Tuesday, March 4, 2014
Back in high school, I wrote a post on nuclear energy. It was the most-read post for a long time on this blog. It has since fallen to 2nd place behind “Mt. Rainier Weather.” However, they are very close in views, so there are brief times when it reclaims first place. Although it pains me to admit it, the reason why these two posts (and many of my top posts) have so many views is not because they are popular or well-written but simply because the images on the post appear on Google Images, allowing curious websurfers to visit the source of the picture (my blog) if they so choose. Let’s just pretend I’m a internationally-known weather celebrity whose posts are celebrated throughout the world without the help of Google Images, though. It sounds better.
I wrote this post soon after the Fukushima meltdown in Japan. I knew it would be a controversial post; I was actually defending fission power. Nuclear fission is the cleanest type of non-renewable power source available, and is the most feasible for large-scale electric production. Hydroelectric dams can produce a fair amount of electricity (that’s why our electric bills here in Washington are so cheap), but wind and solar don’t produce much. And what about solar at night or when it’s foggy? And have you ever seen a wind farm full of non-rotating windmills? It’s pretty pathetic. The destruction of nuclei in nuclear fission releases vast amounts of energy for very small amounts of fuel, and since no combustion is involved, no carbon dioxide is emitted. You also don’t get those particulates that you often get from combustion, especially the combustion of low-quality coal. Nuclear waste can be stored safely, and the U.S. has not had an accident since Three-Mile Island. Excepting the Chernobyl meltdown in 1986, nobody has ever died as a result of radiation exposure from a nuclear power plant, disaster or not. In fact, nuclear has one of the lowest accident/failure rates of any engineered design.
As I’m sure we all know, however, the accidents, when they occur, have the potential to be very serious. This isn’t McDonald’s, and you’re not making the mistake of giving your customer a Big Mac instead of a Quarter Pounder with Cheese. The site of the Fukushima nuclear meltdown is still highly radioactive, and cleanup will take 40+ years and tens of billions of dollars. In addition, some of the land will be unfarmable for centuries. Sure, coal power is dirty and inefficient, but there’s no danger of a coal plant failure grossly contaminating the surrounding area to the same extent of a nuclear plant.
Three Mile Island, and particularly Chernobyl, occurred due to human error. The guys at Chernobyl had limited knowledge of nuclear engineering and physics, and ran the reactors with many of the safety systems turned off. In addition, there were many engineering flaws with the reactor in the first place. All these flaws have been fixed in future plants, and there is essentially no chance that an event like this could ever happen again. I thought that the Fukushima plant would have been much more advanced because it was a nuclear plant in a developed nation in the 21st century, but engineering-wise, it was found to fail the most basic of safety requirements by several nuclear safety agencies and that there was no way it could ever withstand an earthquake or tsunami.
Basically, what I’m trying to say is that all of these accidents could have been easily avoided with more care and preparation. You do NOT want to skimp on safety when it comes to nuclear energy. If you want to read my previous post on nuclear energy, you can do so here.
Alright, that’s my spiel on fission power. Let’s move onto fusion power, or thermonuclear energy.
|Front page of the New York Times, December 7, 1960. Retrieved from Alex Wellerstein’s Restricted Data Nuclear Secrecy Blog|
That’s Einstein’s mass-energy equivalence formula. It says that the amount of energy in something is equal to its mass multiplied by the speed of light squared. The formula says all types of weird things… for example, if you add energy to an object, its mass will increase by a tiny amount even though no matter has been added. Likewise, it says that when mass is lost, as it is in nuclear fission and fusion, tremendous amounts of energy are released. This is because the amount of mass lost is multiplied by the speed of light squared (c^2), and as you can see at the bottom of the picture above, c^2 is quite a large number!
Now that we’ve got that settled, let’s take a look at how nuclear fission and nuclear fusion work.
|Simple diagram of nuclear fission. http://en.wikipedia.org/wiki/Nuclear_fission|
|Reactors and Cooling Towers at the Susquehanna Steam Electric Station: retrieved from Wikipedias’ nuclear power page.|
The most common type of hydrogen atom has one single proton and one electron. For the fusion reactors currently being tested, we take two different types of hydrogen atoms, or isotopes: deuterium and tritium. Deuterium, often known as “heavy hydrogen,” is hydrogen with one neutron in addition to the one proton and electron, and tritium, which is very rare naturally but can be synthesized from lithium, has two neutrons, a proton, and an electron. Any atom that has one proton is a hydrogen atom.
Anyway, for any sort of fusion reaction to occur, the nuclei must be squeezed together. The main obstacle they have to overcome is that the protons are positively charged (neutrons have no charge). Like charges repel, so fusing an atom requires overcoming the repulsive force between the protons in the nucleus.
To overcome this, you need two things: extremely high temperatures (100 million degrees Celsius, as stated above) and incredibly high pressure (the hydrogen atoms need to be within one quadrillionth of a meter). The sun does this using the force of gravity to compress the matter into its core, which is where the fusion takes place. Since we don’t have a prodigious amount of matter at our immediate disposal, we need to apply energy from magnetic fields or lasers.
I talked about deuterium-tritium reactions, but ideally we’d eventually be able to rely on deuterium-deuterium reactions. Deuterium is easier to extract from seawater than tritium is to create from lithium and is far more plentiful. The only problem is that D-D fusion requires much higher temperatures to ignite, with the absolute minimum required being 400 million degrees Celsius compared to a minimum of 45 million degrees for D-T fusion. Any engineers in the house?
Speaking of engineering, there are two types of fusion reactors that are currently being explored: magnetic confinement and inertial confinement. Let’s now take a look at how those work.
A magnetic confinement reactor is a reactor that uses electric and magnetic fields to heat and compress electrified hydrogen gas (hydrogen plasma). The main magnetic confinement reactor that scientists from all over the world are collaborating on is located in France and is called the International Thermonuclear Experimental Reactor (ITER).
|Credit: Matt Farrell, University of Illinois|
|Toroidal power transformer in my Sansui G9000DB stereo receiver|
The fusion reaction becomes initiated when neutral particle beams, electricity, and microwaves from various accelerators heat a mass of hydrogen gas. When this gas is heated to a sufficient temperature, it turns into plasma. Plasma is the same type of substance that stars are made out of and is regarded as the fourth state of matter (regardless of what your elementary science school teacher may have told you, there are more than just three phases of matter!). Power is supplied to the transformers to create a magnetic field (a flowing current of electricity creates a magnetic field around it), and under this extremely strong magnetic field, the plasma is compressed and fusion takes place. Well, at least that’s the idea.
While magnetic confinement works by magnetically compressing the hydrogen ions in close proximity to each other for a given amount of time, inertial confinement works by fuse them so fast that the ions are not able to overcome their inertia and move apart, leading to the name “inertial confinement.” When I think of inertial confinement reactors, I often get this image of this kid shoplifting a candy bar from a store at night and running away before being surrounded by police pointing a bunch of flashlights at him. Except, in this example, the “kid” is a pea-sized pellet containing deuterium and tritium and the “flashlights” are dozens of incredibly powerful laser beams. The biggest inertial confinement reactor in the world, the National Ignition Facility (NIF) at Lawrence Livermore Laboratory in Livermore, California, contains 192 of these lasers. In the NIF, these lasers are housed within a 10-foot diameter rugby-shaped “target chamber” called a hohlfram. Much like the donut-shaped topomak, I suspect that the geometry of the hohlfram had to do more with efficiency than the engineer’s favorite sport.
The lasers at the NIF will focus 1.8 million joules of energy onto the little pellet of deuterium and tritium, heating it and generating x-rays emanating from pellet. The deuterium and tritium will then turn into plasma as a result of the immense heat and radiation and compress until fusion occurs. Once this fusion occurs, the intense amount of heat and energy released from it will act to sustain fusion. We have not reached this point yet, but we are making progress; back in 2013, we generated a net gain in power produced for the first time in history.
|Fusion process for an inertial confinement reactor. Credit: Lawrence Livermore National Laboratory|
The general mechanism for the generation of electricity for a topamak is the same as any fission or fossil fuel reactor; a reaction produces heat that boils water, creates steam, and drives a steam turbine, creating electricity. So yes, fusion reactors will still have those awesome steam towers.
But while steam towers are nice, they don’t explain the full scope of the benefits of nuclear fusion power, especially when compared to fission. Deuterium is very common in the ocean, and tritium can be easily processed from lithium. Our current deuterium/lithium reserves would last us 60 million years, but if we used just deuterium (as we hope to in the future), our fuel reserves would last 150 billion years. To put things in perspective, that’s almost 11 times the age of the universe. Even if we become an incredibly power-hungry civilization and last for five billion more years (until the sun dies), we will have hardly put a ding in these reserves. So for all practical purposes, fusion, particularly deuterium-deuterium fusion, is a renewable source of energy. Uranium, on the other hand, is rare and must be mined. Fusion reactors produce less radiation than conventional fission reactors, and while waste is produced, it decays on decadal timescales and is approximately as radioactive as coal ash after 100 years. Uranium and plutonium take thousands of years to degrade to safe levels. There’s no danger of a runaway meltdown like there is in a fission reactor; fusion requires incredibly specific conditions to exist, and if these conditions are disrupted due to an external factor like a massive earthquake, the fusion will cease. And let’s not forget about the prodigious amounts of power produced from fusion.
Is nuclear the fusion the answer for all of our energy problems? Yes and no. I believe that it is the “holy grail” of energy and something that we should aspire to, but with greenhouse gases accumulating as fast as they are, we need to invest in proven technologies that do not emit carbon dioxide. Many of the professors I have talked to at the University of Washington believe solar will be the leading energy source in a couple decades. One thing is for sure: we need to get off coal.