Wendelstein 7-X (W7X) stellarator. Source: Wikipedia

5 questions on Fusion Power

1. I heard something about fusion power. What exactly happened?

The world got one step closer to a new source of clean energy this month as two different fusion reactors successfully created hydrogen plasma for the first time. German scientists switched on the Wendelstein 7-X (W7X) stellarator, the largest nuclear fusion machine of its kind, producing and sustaining plasma for a little over a quarter of a second. Not to be out done, Chinese scientists announced their own fusion experiment called the Experimental Advanced Superconducting Tokamak (EAST). The test produced hydrogen plasma that was maintained for an impressive 102 seconds. Both experiments mark big gains towards keeping a stable, sustainable fusion reaction.

2. That’s nice, why should I care?

Producing hydrogen plasma is a big step towards harnessing the energy of nuclear fusion, the same process that powers the Sun. It’s a huge challenge that scientists and engineers around the world have been working on for the past 6 decades. The rewards would be worth it: controlled nuclear fusion has the potential to provide the world with cheap, clean, and sustainable energy. If you needed any more selling points, nuclear fusion has been powering our Sun for the past 4.5 billion years. If we can begin to harvest fusion, civilization is pretty much set for its energy needs.

3. How is this different than nuclear power?

All current nuclear power plants use a process called nuclear fission to create energy, which is different reaction than fusion. In nuclear fission, 1 atom is split in two smaller elements (think of the word fissure, to separate).  Nuclear power plants use an isotope of uranium called uranium-235, also known as enriched uranium. If you can remember back to high school chemistry days, isotopes are atoms of the same element (same number of protons) that have different masses (different numbers of neutrons). 

Fission works by firing a neutron at the nucleus of an atom of uranium-235. This causes the nucleus to become unstable and split into two smaller atoms, barium and krypton as you can see in the graphic below.

fission

This split releases a huge amount of energy; about a million times more efficient than coal. Some of this energy is released as  light, but much of it is released as , heat, which is captured by water, turning it to steam, which in turn powers a generator that creates electricity. In addition, to the radioactive material and energy that is released, there are also several neutrons that are flung out of the nuclei of these atoms. If the uranium-235 is packed tightly enough, these neutrons will smash into other nuclei, causing a chain reaction of fission that is self-sustaining until at the uranium-253 is spent. And because nuclear power plants do not burn anything, they are carbon free sources of power.

A carbon free energy source, you say? That sounds good, I’ll have that! It’s not quite that simple. One of the problems with nuclear fission is that while there is no carbon dioxide released, it comes with some unwanted byproducts.  The waste generated from these plants contains radioactive barium, cesium and plutonium. Exposure to these elements can be fatal, even for short periods of time, and since the half-lives of these elements can be up to 24,000 years, this stuff sticks around for a while. Unsurprisingly, no one wants to store radioactive waste in their back yard for thousands or millions of years. We still have no answer to how you store this material making nuclear power a carbon-free, but certainly not clean, power source.

4. So what’s fusion power? And what’s so great about it?

While nuclear fission splits atoms apart, nuclear fusion is where the nuclei of two smaller atoms come together and fuse to create a heavier element. It’s the same process that occurs in cores of stars. Due to the huge pressures and density created by the enormous mass of stars like the sun, hydrogen atoms are smashed together to create helium. This reaction releases huge amounts of energy. If we can recreate a stable fusion reaction, we could use the heat to power a steam turbine and eventually a generator to create electricity.

fusion

This isn’t as easy as it may sound. Just like magnets, the protons in each nucleus will want to repel each other because they have the same positive charge. We overcome this tendency by recreating some of the incredible temperatures and pressures found inside a star. One method of achieving nuclear fusion is called internal confinement, which uses lasers to zap pellets of hydrogen with so much energy they fuse together.

The second method is called magnetic confinement and is the type of reactor used in the two latest experiments. In this kind of reactor, a sample of hydrogen is heated to extremely high temperatures to allow for the individual atoms to move fast as possible so they will collide and fuse. At these temperatures, (the Chinese trial reached nearly 50 million degrees Celsius), the hydrogen acts as the fourth state of matter, plasma. Since the plasma is ionized, it can be constrained and controlled by magnets, allowing fusion to occur without destroying the reactor itself.

phases-of-matter (1)

Why go through all this trouble? Like nuclear fusion, there’s no carbon dioxide being released into the atmosphere, which is the problem with coal, oil, and natural gas, all of which contribute to global warming. However, unlike current fission reactors, there’s no dangerous nuclear byproducts. In fact the leftover helium could even be harvested and address the world wide shortage.  And since hydrogen is the most abundant element in the universe, there will always be plenty of raw materials. But perhaps most importantly, it would create an unlimited supply of clean, renewable energy that could power the world without the negative effects on the environment.

5. That does sound great! When will we get fusion power?

Fusion power is extremely challenging to harness. Remember that researchers are trying to recreate conditions inside of the sun. With temperatures that high, it’s hard for to contain the plasma. Until researchers are able to control the plasma for more than a couple seconds, we won’t be able to keep the reaction sustainable nor use fusion as a reliable power source.

There’s also the problem of the energy efficiency. Current experiments use way more energy than is harvested from the reactions. There is a long way to go, but progress is being made, the German experiment had a record 15% efficiency. It’s entirely possible that a fully functioning and energy positive reactor will be developed by the 2030’s with possible implementation into the energy grid by mid century. This would be a huge help to meet the exploding energy demands of a world in which developing countries are rapidly industrializing.

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