A Canadian company is designing a reactor that uses steam pistons to achieve nuclear fusion:
the very same reaction that powers our sun and all the stars. If they’re successful it could
be the best form of clean electricity in the world. But how can these steam pistons harness
the power of the sun? Well, that’s what I’m here to explain. But before we dive into this
advanced reactor design, let’s take a quick step back and review the physics of fusion!
Fusion occurs when two atoms fuse together to make a new, heavier atom. When light elements,
such as hydrogen or helium, fuse together they also release energy. But fusion can only occur
under special conditions. Normally, when atoms are hanging around on earth, their nuclei don’t
touch because they’re surrounded by electrons. But when a gas gets very hot it transforms into
the fourth state of matter: plasma. A plasma is so hot that the electrons get stripped away from the
nucleus – but to achieve fusion, the plasma must get even hotter, up to millions of degrees! This
is because even with their electrons stripped away, the positively charged nuclei repel each
other. But at EXTREMELY high temperatures the nuclei in the plasma have enough energy
to overcome this repulsion and fuse together. Here’s how the fusion process works in the sun:
when two hydrogen nuclei, or protons, collide, they fuse together and one of them may transform
into a neutron by ejecting a positron and a neutrino. Next, the newly formed proton and
neutron pair may collide and fuse with another proton, transforming into a helium-3 nucleus and
releasing gamma radiation in the process. Finally, two helium-3 nuclei collide and fuse together into
a regular helium-4 nucleus, and they eject the two extra protons. The final helium-4 nucleus has less
mass than the original 4 protons that it was made of – the missing mass was converted into energy
according to Einstein’s famous formula: E = mc^2. The sun is able to achieve fusion thanks to its
immense gravity, which heats up and compresses the hydrogen, causing fusion. But here on earth
where gravity is quite a bit weaker, it’s trickier to create fusion. So to make things
easier for us on Earth, fusion reactor designs use a slightly different process to achieve fusion.
Instead of trying to fuse together single protons like in the sun,
fusion reactors will use Deuterium and Tritium, which are isotopes of hydrogen.
This type of reaction is called DT fusion. In DT fusion, the deuterium and tritium fuse
together to create helium-4, and the extra neutron is ejected. DT fusion will be used
because it is easier to achieve than other fusion reactions, and it also releases a lot of energy.
But just because DT fusion is easier to achieve than other types of fusion,
doesn’t mean that it’s simple. Fusion reactors are incredibly difficult to make – that’s why
no fusion generating plants exist yet. The main difficulty lies in heating a plasma up
enough to achieve fusion. Heating anything up to millions of degrees takes a massive amount
of energy – so much energy that so far, scientists and engineers haven’t been able to create a fusion
reaction that generates more energy than it takes to get the reaction going. You see,
scientists have been able to achieve fusion in a lab as far back as the 1930s, but all these
experiments have taken more energy to run than they have produced! A practical fusion reactor
that can generate electricity will need to be much more energy efficient, so that the fusion reaction
generates more energy than it takes to keep the reaction running. There are a number of ways that
scientists and engineers have proposed to actually make a practical fusion reactor. One of the more
popular ideas is to use a sort of magnetic donut called a tokamak to heat and control the plasma.
Another idea is to use high powered lasers to heat and compress a pellet of fusion fuel. But
neither of those are what this video is about. That’s because General Fusion, a company located
in Burnaby, British Columbia, is proposing to use steam pistons to make a practical fusion reactor.
General Fusion’s reactor would be made of a sphere containing liquid metal.
The liquid metal would be spun around to create a hole in the middle, and a plasma
would then be injected into this hole. The steam pistons would then compress the spinning ball
of liquid metal. This would in turn compress and heat up the plasma until fusion is achieved.
The fusion reaction would heat up the surrounding liquid metal, which would then be pumped into a
heat exchanger to boil water. The steam would then spin a turbine and generate electricity.
The reason for this approach is that steam pistons are easier and cheaper to manufacture
than the powerful magnets and lasers required of the other approaches – General Fusion says
this will make their reactor more economical and simpler to construct.
Speaking of construction, when will General Fusion actually build their first power plant?
Well, General Fusion will begin construction on a Fusion Demonstration Plant in the UK in 2022,
and it’s expected to be complete by 2025. However, this isn’t a full power generating
station – it’s smaller than a commercial fusion plant and it won’t produce any electricity.
The demonstration plant is meant to prove that General Fusion’s approach will work and that it
will be cost effective. If the demonstration plant works as planned, then General Fusion’s goal is to
bring commercial, fusion electricity generation to the world by the early 2030s. Of course,
given the difficulty of engineering a fusion power generation plant, we’ll just have to wait and see
whether General Fusion achieves their goal. But if practical fusion power is so difficult
to achieve, why even bother when we already have other ways of generating electricity?
Well, generating electricity from fusion would have a lot of benefits compared to other methods
of power generation. For one, it doesn’t emit greenhouse gases like fossil fuels - the only
waste product is helium. It also doesn’t rely on sunny or windy days like solar and wind power do –
since it’s weather independent, fusion generation could make a great complement to renewables.
Fusion reactors also have some benefits over our current fission-based nuclear reactors. One
advantage is that fusion reactors can’t meltdown. This is because fusion isn’t
a chain reaction like fission is. If some part of the fusion reactor stopped working,
then the plasma would simply cool down and the reaction would stop. Also, fusion reactors
wouldn’t produce the long-lived radioactive waste that our current fission nuclear reactors create.
Speaking of nuclear waste, did you know that in New Brunswick, there are currently
two nuclear reactors being designed that could use spent nuclear fuel to
generate electricity? Be sure to watch this video next if you want to find out more!