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Ignoring the way such a creature may evolve, is there a possibility of a living creature, using Nuclear Fission/Fusion to create energy (and preferably use this energy to support itself).

The smaller the creature the better.

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Trite answer: sure! France generates about 70% of its electricity using nuclear reactors. French adults average 175cm in height, if that's small enough for you.

If you're prepared to separate energy generation from energy consumption, then look out of your window at a complete ecosystem almost entirely driven by fusion power generated in a handy nearby star. Cyanobacteria can be submicron-sized, and might be the smallest independent photosynthetic organisms.


Less silly answer: not naturally.

Obtaining suitable fission fuels is very difficult. They must be mined and smelted and enriched, all of which are complex industrial processes that are quite energy intensive. To have a single organism manage all these feats seems basically implausible. If you rewind time by a few billion years there's enough naturally enriched fissiles about that spontaneous natural nuclear reactors could form, and it would be slightly less difficult to get fuels.

Obtaining deuterium for fusion is perhaps a little more plausible, as semiheavy water molecules (where one of the two hydrogen atoms is, in fact, deuterium) make up about 1 in 6400 water molecules in the wild, and a biological filtration process could be imagined... natural biological processes prefer regular hydrogen, and heavy water can be toxic.

But once you've got the fuel you are faced with the enormous difficulties of starting a nuclear reaction safely. We don't actually know how to do fusion without the aid of a star-sized gravitational field, but we do know it requires a lot of heat and pressure, and developing those things in a biological structure seems implausible.

Assembling a critical mass of, say, uranium might be a lot easier, but then you have to grow suitable shielding so the radiation doesn't kill you, suitable cooling so the heat doesn't cook you, and then work out a way to actually derive some benefit from the process. Naturally evolving a steam turbine seems a little unlikely.


What you're left with, then is a deliberately engineered system that is basically a conventional nuclear power system with some organic glop on the side. Reproduction is left as an exercise for the reader. Fission systems require fuel that's impractical to obtain, and fusion systems require reactor conditions that are impractical to generate. Both require large amounts of material that are awkward to obtain or produce, and neither can trivially be miniaturized.

What you'd basically end up with is some kind of deliberately engineered nuclear tree, that probably wouldn't be able to reproduce without the aid of a factory.

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Definitely.

Beginnings:

  • A strain of betaproteobacteria has been discovered which has a knack of using Uranium instead of oxygen in a redox process where uranium is the electron acceptor. This releases energy in the same way an organism doing the same thing with oxygen would make use of it.

That's gotten the Uranium into the life-cycle.

  • An organism who's gut contains these bacteria will be able to intake a diet high in compounds containing Uranium and fission products (which are still radioactive). They will need to have the same protection in their chemistry as the bacteria mentioned above that protects them from the harmful effects.

That's gotten the uranium into the larger organism's guts.

  • Such an organism will incorporate those break-down products into their bones and other tissues. Strontium, a fission product is readily absorbed and fixed within bone-tissue in humans in real-life. As these chemicals accumulate (during gestation in the womb...?) they start to produce heat.

Heat energy can be used to fuel chemical and physical reactions:

  • "cracking" ethanol into acetaldehyde.
  • Photosynthesis, in the form of light wavelength photons usually, but life adapts.
  • Melting ice.
  • Evaporating liquid water.
  • Sublimation of carbon dioxide (dry ice)
  • Cracking of alkanes.
  • Thermal decomposition reactions.
  • Electrolytic decomposition of sodium chloride into sodium hydroxide and hydrogen chloride.
  • Dissolving ammonium chloride in water.

Now I don't know about you, but it seems to me that the life-form might be well suited to places with low temperatures, such as Arctic seas or Arctic tundra where they may be able to remain active throughout any long-dark created by the orbital inclination (as long as they dig for uranium-rich dirt to eat from time to time). There's also license that this gives a writer to adapt the organisms concerned to eat other substances, Potassium, Calcium 41, Calcium 48, Thorium for example. Not to mention a potential non-necessity for the presence of Oxygen, or perhaps even much of an atmosphere (all the biochemistry can be done with the rocks, inc. water extraction). Plenty of scope for flexibility in story-telling.

Ps.: - I never ignore evolution, context is all.

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  • $\begingroup$ It seems like this addresses radiosynthesis (like that slime mold found in Chernobyl), which is indeed useful and cool, but it’s not fission or fusion as the OP requested. $\endgroup$
    – StephenS
    Jan 26, 2022 at 14:01
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Fusion would not be possible in a living organism, considering the energy barrier which needs to be overcome in order to merge two nucleons into a single one.

Fission is just a step below, because it would require that the organism can both gather/store enough fissile material and produce neutron on demand to start the fission.

What might work in a worldbuilding context is for an organism to extract energy from radioactive decay.

For example bananas are notoriously more radioactive than the background, due to their high content in Potassium and the presence in it of Potassium 40, with a radioactivity of about 31 Bq/g (about 31 decays per second in a gram of the element).

If the organism has a way of capturing the energy released during the decay of the radioactive atom, it can use it for its own scopes, and would only need to be able to feed on radioactive substances, or better to sense which matter is more radioactive than the background and use it as food.

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