MOS: Tokamak Reactors

I saw in the news that scientists made a nuclear thing that was hotter than the sun. So let’s talk about why it won’t kill you.

(Probably).

Today’s Moment of Science… the promise of fusion reactors.

Early atomic weapons and all our nuclear reactors used for energy to date have relied on fission. Per SciSpouse, fission is as simple as “hot rock go in water make boil.” Which is annoyingly accurate if you consider the all-natural nuclear reactor in Oklo, Gabon. A deposit of fissile uranium in a mine was braised in nature’s favorite neutron moderator, water. When the reaction went critical about 1.7 billion years ago, the planet went all ‘set it and forget it’ with a sustained nuclear fission reaction that went on for a few hundred thousand years.

Under these perfect conditions, this is the only nature-made fission reactor that’s been found to date. On the other hand, we will almost assuredly never find an all-natural fusion reactor outside of a star.

Unless something goes horribly fucking awry, there are no perfect conditions on the surface of the Earth in which some heavy hydrogen will naturally undergo the magic and mayhem of fusion. Two light elements cram into a tiny house together, form one element, and a neutron gets Kondo’d out in an energetic fit of atomic rage. It’s the type of nuclear reaction that powers solar energy.

Theoretically, there are huge advantages to using nuclear fusion for power. Compared to fission reactors, it produces more energy and little waste. The fuel is ridiculously abundant; isotopes of hydrogen can be readily harvested from seawater.

Howthefuckever.

In order to get some atoms to fuse, you need a lot of heat and pressure to help them overcome subatomic social anxiety. Electrostatic charge between two positively charged nuclei will cause some repulsion. But apply enough heat and pressure, you can coax a pair of atoms together.

When I say “enough heat,” I mean far more than can be handled by fission reactors. They’re typically designed to handle a relatively cool 300-600C, going up to a thousand degrees in very high temperature reactors. But when your energy requirement to start a reaction is “get this mother hotter than the fucking sun,” you need to build a bigger boat.

So, the tokamak.

First invented in the 1950s by Soviet scientists, the donut shaped reactor uses a magnetic field to contain plasma that’s heated upwards of 150 million degrees. Though there’s been news about fusiony goodness from the reactor here and there over the decades, it’s one of many technologies that perpetually seems 10-15 years away.

Earlier this month though, there was a breakthrough.

At the JET laboratory in the UK, a sustained fusion reaction was produced that lasted for five seconds. Which unfortunately only sounds impressive to nuclear scientists and cowboys. It also took about three times as much energy to induce fusion than the fusion itself produced.

So why is a five second energy drain considered a big deal?

The previous record, set in 1997 at the same facility, only produced 22 megajoules while this produced 59MJ. While larger reactors were being built with high hopes of their design updates eventually working, JET’s reactor was retrofitted over twenty years. It acted as a sort of testing ground for technology to come in reactors an order of magnitude bigger.

The ITER facility in France is expected to be fully operational by 2035, with a much larger reactor aiming to produce ten times the energy it uses. JET has been described as a ‘scaled-down’ version of ITER. Though this was “just” a demo from a small reactor that produced enough energy to boil sixty kettles (which is possibly the most British unit of measurement ever), it’s a glimpse into the future of nuclear fusion.

Which is, as always, 10-15 years away.

This has been your Moment of Science, just saying the phrase ‘nuclear fuckery’ now because otherwise you’ll think I’ve fallen ill.

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