The world of the atom carries many names. Some of them are famous, like Rutherford, Bohr or Fermi, but there were many others, both before (such as Pierre and Marie Curie) and after (such as Otto Hahn or Lise Meitner). In fact, it was Lise’s nephew – Otto Frisch – that confirmed experimentally in 1939 that breaking up a particular uranium nucleus (nuclear fission) released a huge amount of energy, granting him a part in the Manhattan project.
Much has happened since then, not just historically but also scientifically and technically. These advances leave us dreaming of the possibility of nuclear fusion, in other words, merging atom nuclei, replicating the mechanism that powers stars, right here on our planet and, why not, outside of it as well.
Fig.1 – Raw visible light image of plasma inside a Polywell reactor
The advantages of achieving such an energy source are both beautiful and outstanding:
- Fusion could release up to 4 times more energy than fission and 4 million times more energy than burning fossil fuels, and if achieved, it would be regulatable, meaning we could generate a base load and interact with the grid without problems
- Fusion fuels are (in some cases) nearly impossible to run out of
- There’s absolutely no release of any greenhouse gas whatsoever
- There’s no long-lived radioactive waste (fusion would leave materials radioactive for approximately 1 century only when compared to the thousands of years of the existing nuclear fission power plants)
- Although some of the fuel for fusion is radioactive, and therefore represents a major security problem, it cannot be used directly to make a bomb, making it way less problematic than securing, for instance, enriched Uranium, not to mention there are alternatives which generate no significant radioactive material whatsoever
- Absolutely risk free from a technical standpoint, that is, if there was an operation problem or an accident (such as an earthquake or an explosion) there would be no risk at all for the population, for there’s no risk of a chain reaction and there’s very little fuel in the reactor.
However, all of these criteria, put together, sound almost like a miracle, nothing more than science fiction which obviously leaves us wondering… is it? Is it possible? Can it be done? The answer is clearly yes. Yes it can. Someone somewhere is probably doing it while you read this.
Nevertheless, can we do it outside of the lab, generating the energy output we need to power cities, cars, trains and space missions, all of this in a perfectly stable manner and at an affordable cost? Well the truth is there’s no answer to that… at least for now. In fact some believe commercial nuclear fusion to be no more real than a unicorn.
The only thing known for sure is that it’s a question bound to generate passionate answers, both from the side of the “No” and the “Yes”, and any answer is bound to be a very complex one. In this article I’ll try and interest you in this matter, while in the second part I’ll try to show both sides of the argument, and let you decide for yourself which one to believe.
It’s hard to comment on the pros and cons of such a technology without first introducing the supreme basics the underlie it. This means oversimplifying things which are not that simple. That said, we all know that atoms are composed of electrons (really very small negatively charged particles) “orbiting” a nucleus, which is in itself composed of protons (positively charged particles) and neutrons (particles without electric charge).
What defines an atom is the number of protons its nucleus holds, for instance, an atom with one proton in its nucleus is a hydrogen (H) but an atom with two protons is helium (He). Nevertheless, all atoms can have more or fewer neutrons in the nucleus. All the possible variations are known as isotopes. Isotopes are defined by the sum of the protons and neutrons in the nucleus, for instance: a hydrogen atom with two neutrons and one proton is said to have a mass number of 3. You could call it “hydrogen-3” (or in this specific case by the fancy name of tritium).
Fig.2 – Hydrogen isotopes (Wikimedia)
Also, an atom nucleus can have more or less electrons “orbiting” it while still having the same mass number (remember it’s the sum of neutrons and protons in the nucleus). Those variations are known as ions.
Well, fusion is achieved by heating a fuel (isotopes of light atoms) into a plasma (a state of matter, just like a liquid or a solid, composed of a cocktail of ions and free electrons) at insane temperatures over 100 million degrees. At these temperatures the various elements in the fuel fuse together releasing copious amounts of energy which, when converted to heat, can then be converted to other, more useful forms, such as electric energy.
Fig.3 – Schematic of D-T fusion (Southeast images)
But how? Well, remember Einstein’s famous E=mc2? What this tells us is that mass and energy are two sides of the same coin, therefore a loss of mass has its equivalent in energy. But how much energy? The answer lies in an isotope’s binding energy, i.e. the energy required to release a neutron or proton from the nucleus. Imagine that some atoms and isotopes are sort of “more efficient” than others, hence they require less energy to do the same action (in this case unite the nucleons together).
Fig.4 – Binding Energy Chart (Scienceblogs)
If you look at the chart you see that uranium has a smaller binding energy (BE) than the atoms before it, therefore, if you break it into smaller atoms (with higher BE) these will be “more efficient”, they will weigh less, that lost mass being converted to energy and released under many forms (and you have your standard fission reaction). If you start on the other end though, you see that if you join isotopes with low BE into other ones with higher BE, the result will also be “more efficient” (and weigh less) therefore extra energy is released (and you have your fusion reaction).
Now that you have a PhD in nuclear physics, let’s look a bit deeper.
The fuel problem
Deuterium (D) (in other words plain old-fashion Hydrogen) is a naturally occurring isotope that can be found on water (a.k.a. heavy water) for instance, so it’s relatively cheap to produce and non-pollutant.
Nevertheless, the same can’t be said of Tritium (T), which is naturally non-existent, highly radioactive, and only has a half-life of about 12 years. Definitely it isn’t the coolest fuel source, but the worst part is that it simply doesn’t exist… anywhere (at least for practical purposes). Nowadays Tritium can be extracted at some selected nuclear power plants, but at an extraordinary cost – tens of millions of USD per kg. As if this wasn’t enough, these plants are not getting any younger and will probably stop operation in the coming decades meaning that, accounting for the decay of existing stocks, the global inventory of this material is probably around 20kg. The US operates a special extraction facility but right now it’s part of its nuclear weapons programme.
Helium-3 is also stable and exists in nature, albeit in very low quantities, approximately only 0.000137% of the total helium available. However there’s a lot of it on the moon’s surface which is creating a lot of buzz regarding the possibility of a future mining exploration in our satellite’s surface.
Boron is stable, not known to be toxic, it’s also naturally occurring and “only” costs around 5.000 USD/kg.
Well, given the choices above, which fuel should we use? D-D appears a good choice. Nevertheless, the probability of achieving nuclear fusion using D-D reactions is 1000 times inferior to that of D-T and 100 times inferior to D-3He! So, using the standard Tokamak reactor design (we’ll see more about it in the next part) and at the temperatures we hope to achieve with our best prototypes, we are stuck with D-T reactions and, as we’ve seen, Tritium sucks.
Fig.4 – Interior of a Tokamak reactor (stopped and in operation)
Also, because we actually want a continuous reaction (and as we’ve seen Tritium is not the most abundant material on Earth right now), we need to generate more tritium than the one we actually spend. (Hopefully) It can be done through a process call “breeding”. This involves a Lithium blanket surrounding the reactor, between 0.5 and 1m thick, which amounts to a modest thousands of tons of lithium. Since lithium is not the most plentiful thing to come by, any project using this technology probably would see its costs rise by tens (and perhaps even hundreds) of millions of USD. But it gets worse, since we are not even sure if Tritium breeding is achievable at these scales, since most research is based on computer simulations.
What to expect?
But things don’t get any easier for Nuclear Fusion enthusiasts, for fuel is just the first of the many problems that this technology encounters. Sustaining the plasma, material resistance and obviously outrageous costs are just some of the issues that have to be tackled and won. All of this, in a large timeframe where all other renewable and storage technologies keep evolving (who knows the efficiencies and stability we can obtain in a couple of decades time).
But before you quit, just take a minute to picture the potential of a regulatable, clean, safe, cheap, almost unending and perhaps even super transportable energy source? We are talking cheaper ultra-fast electric transportation (like Hyperloop, the Maglev or electric transcontinental flight), 0% carbon emissions in only a couple of decades (instead of the several centuries ahead of us at this pace) or even Earth to Mars travel in just a few hours.
So the optimists shouldn’t despair just yet, for not all designs are made equal. Although the Tokamak is the most extensively studied design, fusion is being pursued in a number of ways, which are as different from each other as water is from wine. In fact some of them have shown interesting results, and are cheaper, more compact and less problematic than the Tokamak.
In the next part of this article we’ll look into some of the competitors in this race and their differences and try to compare them to competing renewables and fission. Again: remember the immense benefits we could reap from achieving commercial fusion.
Hugo Martins | Analyst