Ask HN: Is it possible for fusion reaction to store energy? - jlebrech
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FiatLuxDave
Possible? Yes, but I'm not sure if my answer is what you are asking about.

When people normally speak about fusion energy, they are referring to fusing
small nuclei, such as hydrogen, deuterium or tritium. Any nuclei which fuse to
create something smaller than iron will release energy when fused. If you
create something the size of iron or larger, it requires energy to do this.
So, in a sense, stars that create elements heavier than iron (like supernovae)
are storing energy using fusion.

You could fuse two small nuclei to make a larger nucleus that decays later.
Fusing deuterium to make tritium (a beta emitter) would be an example. To make
it useful, you would probably want to generate an isotope which had a natural
decay rate which was appropriate for your storage system. It is generally
going to cost more energy to make these than you will get out, and if you can
already fuse small nuclei, then fusing those directly is a better energy
source.

I suppose in theory one could use energy to break apart small nuclei, then
fuse them later. This would qualify. I'm not sure what motivates your
question. The practical answer is that light nuclei are already widely
available, so if you can fuse them, then using them as a fuel is the most
efficient way to have an energy storage system.

There was a bit of research into ways to release energy from nuclear isomers
(Hf 178m2) a few years ago, but it appears to have not panned out. If this had
worked out, one could make a nuclear isomer with fusion and do this.

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JerryFr
No, because:

In fusing plasma, the main carrier of energy out, is the neutron, and methods
to efficiently use this energy are still to be developed, wait for the fusion
plant prototype DEMO. It is not possible to store energetic neutrons.

Fusion ignition is the point at which a fusion reaction becomes self-
sustaining, i.e. the energy being given off by the fusion reactions heats the
fuel mass more rapidly than various loss mechanisms cool it. At this point,
the additional energy needed to heat the fuel to fusion temperatures is no
longer needed and can be turned off. Throttling off the deuterium or tritium
fuels will stop the reaction.

The produced helium nucleus carries an electric charge which will respond to
the magnetic fields of the tokamak and remain confined within the plasma.
However, some 80 % of the energy produced is carried away from the plasma by
the neutron which has no electrical charge and is therefore unaffected by
magnetic fields. The neutrons will be absorbed by the surrounding walls of the
tokamak, transferring their energy to the walls as heat.

In ITER, this heat will be absorbed into cooling water, through heat
exchangers being dispersed through cooling towers.

In the subsequent fusion plant prototype DEMO and in future industrial fusion
installations, the heat will be used to produce steam, driving turbines
turning alternators producing electrical output.

