Why would you want to build a nuclear reactor in your parents’ garage?

Maybe when you were a kid you wanted to build your own play castle or skateboard ramp or ant nest. A decent challenge for a kid. Something you had to lock horns with your parents over. Taylor Wilson wanted to build a nuclear reactor. Not your average childhood ambition. And the most amazing thing is he did–with his parents’ blessing.

Over at PopSci you can learn Taylor’s fascinating story that raises big questions about how to personalize education, how to nurture childhood curiosity, and what is fair game for a school science fair. It’s a long article, but I thoroughly recommend you give it a read as it’s an inspiring, heartwarming tale.

Here we’re going get scientifc on nuclear reactors.

One of the biggest issues confronting the world over the next century will be ensuring that a growing population with more and more energy intensive lifestyles has its power needs adequately met–without wrecking the planet. Nuclear fusion can offer that possibility. Unfortunately, unlike in the heart of the sun, we haven’t been able to create self-sustaining fusion reactions, and the nuclear power produced by countries such as UK, France, USA, and Japan comes from fission reactors, a class of nuclear energy with big downsides.

Energy can be released from nuclear reactions–those that involve the nuclei of atoms–in two ways. Light atomic nuclei from the beginning of the periodic table–elements like Hydrogen and Helium–can be combined to form heavier nuclei, in the process releasing vast amounts of energy. This is nuclear fusion. Alternatively, heavier nuclei can be split apart into two or more lighter fragments, again releasing vast amounts of energy. This is nuclear fission. The energy produced in both cases comes from a small amount of matter being converted into energy according to physics most famous equation  E = mc2. The reason energy is released in both cases (when light nuclei are combined, or heavy nuclei split) is that the most tightly bound nuclei occur a third of way through the periodic table near iron as shown in the curve of binding energy.

Fission occurs by bombarding a suitable heavy nuclei with neutrons that cause it to split and release energy. In the process further neutrons are released leading to a chain-reaction as these secondary neutrons collide with other heavy nuclei producing more energy. In this way a small amount of fuel can produce a large amount of energy.

Fission reactors are problematic for several reasons. First the “fuel” for fission reactions needs to be fissile–that is capable of producing secondary neutrons when bombarded. The most common occuring nuclei that fits this bill is Uranium-235, a radioactive isotope. As such, not only must the “fuel” be handled with great care by human operators, it must also be kept in high-security conditions to stop it falling into the hands of groups who might want to use it as part of a “dirty bomb” or other weapon. Secondly, the fission chain-reaction needs to be very carefully controlled to ensure it neither dies nor escalates–a situation that happened in Fukushima after the cooling mechanisms were compromised, and radioactive material escaped into the atmosphere and ocean. Lastly, even when successful, the products of fission reactions include materials which are themselves radioactive, often with half-lives in the thousands of years. Safely storing these waste products is a huge technical problem.

Nuclear fusion, by contrast, has far fewer drawbacks. The candidate fuels–hydrogen and duetrium–are easy to produce from abundant compounds and are not radioactive. The chance of runaway chain-reactions are remote as the amount of fuel in the plasma chamber (where the fusion happens) can be cut at any time. And lastly the waste products, although expected to include tritium, a radioactive isotope of hydrogen, are far more benign than those produced through fission.

So, why aren’t we making fusion reactors? In short, because the conditions required for fusion to occur are very hard to create and stabilize. The electrostatic repulsion between protons means that before the very short range nuclear force can kick-in and “fuse” the candidate nuclei, temperatures of hundreds of millions of Kelvin and pressures similar to those at the core of the sun, are required. Whereas the sun uses gravitational confinement to produce these conditions, on Earth the only way to create these environments is to use electromagnetic fields, lasers, or other specialist technologies.

Plenty of research is currently happening to make fusion reactors a reality, but maybe it will be a Eureka moment from somebody like Taylor Wilson that makes the final difference.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: