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This is somewhat different to this question on the possibility of biological fusion reactors as I am curious if a living FISSION reactor is more plausible.

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    $\begingroup$ No its not. Not all all. Not one bit. $\endgroup$
    – DT Cooper
    Jan 14 '20 at 2:54
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    $\begingroup$ Nuclear force is short ranged and you need tremendous energy to overcome the electrical repulsion between protons to make new element with some left over energy. $\endgroup$
    – user6760
    Jan 14 '20 at 3:26
  • $\begingroup$ Not for anything resembling Earth biology. If it was some high temperature organism based on another chemistry anything's possible. $\endgroup$
    – John O
    Jan 14 '20 at 14:46
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    $\begingroup$ There is geological evidence for natural nuclear fission reactors having formed in real life, but they were not biological. That said, it could be the base energy source for an ecosystem that has no visible sun (similar to volcanic vents for deep sea ecosystems). $\endgroup$
    – hszmv
    Jan 14 '20 at 14:48
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    $\begingroup$ @meaninglessname "google naturally formed fission reactors" delivers blogs.scientificamerican.com/guest-blog/… $\endgroup$
    – PcMan
    Mar 4 at 6:46
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The short answer is NO - a biological fission reactor is also a flawed design and it's going to cook your biological organism so it's just not going to happen. The energy cost alone to reach break even point is far beyond the biological framework we live in to store and release in such concentrated amounts.

That said, it is perhaps important to note that biological organisms are already molecularly driven even if that doesn't provide the same power as we would get if we were atomically driven.

Terrestrial biology (at least) stores and releases energy at the molecular level. That is to say, plants take molecular compounds like CO2 and H2O and via an endothermic reaction called photosynthesis, change the molecules to different ones like O2 and carbohydrates, which take more energy to form, hence storing the energy taken from sunlight in a molecular form. Plants use some of this for their own metabolism, and animals like us then eat the plants, taking their stored carbohydrates and oxygen from the atmosphere and generate an exothermic reaction that converts them back to CO2 and water, releasing that energy inside us for our own needs.

The energy stored and released during these processes is pocket change compared to fission let alone fusion, but as it turns out we don't really need all that much energy to survive; even the human nervous system seems to operate at around 0.07 volts, meaning that you could run around 21 people in parallel on a standard AA battery if you had to (but for how long I'd need to do more research to say).

Bottom line is that we don't need atomic power to drive our biology and the energy storage capacity of our current biological design would render us incompatible with it in any event. It turns out that being molecularly powered rather than atomically powered gives us all the energy we need and is much safer and sustainable for us into the bargain.

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    $\begingroup$ Human nervous system requires about 50-100 Watt energy in "calm" state. 1 AA battery holds 2-4 Watt*Hour energy. It means that 1 AA battery is enough to feed nervous system of 1 person for no more than couple of minutes. $\endgroup$
    – ksbes
    Jan 14 '20 at 7:10
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Can an organism evolve to use a concentrated mass of radioactive material to superheat a pressurised fluid and use that fluid to turn an organic turbine which rotates a permanent magnet inside a coil of conducting metal to generate electricity? Almost certainly not. Does that mean an organism can't make use of nuclear fission to energise itself? Not at all.

On an atomic scale, fissile elements are basically tiny bombs: they're happily sitting there as one element in whatever molecule, then bam, one or more high-energy fragments ricochet off in a random direction potentially screwing up another nearby molecule, and the original atom is now two totally different elements with different chemistry. We make fission reactions more energetic by concentrating fissile material so that the fragments are often captured by other fissile atoms which prompt them to react in turn, creating a chain reaction; but even in its simplest form a pile of fissile material releases energy by capturing the high-energy fragments in something and thereby getting slightly hot, no feedback loop required. The challenges for an organism safely utilising this energy source, then, are:

  1. Extract fissile materials from its food and concentrate them
  2. Deal with the heavy element byproducts of the fission reaction
  3. Deal with the highly-energetic (usually neutron) fragments and convert their kinetic energy into heat, then convert that heat into a more useful form of energy for the organism

Biological organisms have evolved to manipulate chemistry on a molecular level; they can catalyse pretty much any viable chemical reaction, concentrate particular atoms on one side or other of a boundary, and so forth. It if were evolutionarily favourable for the creature to extract, say, uranium or plutonium from its food, it could do so with no more difficulty than mammals extract magnesium, calcium or potassium ions on Earth. Filtering atoms by isotope is much more challenging, but it's not impossible that an exciting protein could evolve that would bind fractionally more strongly to one isotope than another. Problem 1 solved.

Problem 2 is equally plausible: while the exact byproducts of a fission reaction are random, they'll cover a small range of elements, and if the organism is 'expecting' them then there can be mechanisms for controlling and excreting them if they're not usable. Poisons are only poisonous if the organism isn't adapted to deal with its presence: arsenic is highly toxic to humans, but plenty of terrestrial organisms are evolved to tolerate high concentrations of it.

The main challenge an organism would face is actually doing something useful on a molecular level with the energy released by the fission reaction. By dissolving the fission products in water or a more powerful neutron capture liquid. Boron is an excellent neutron absorber, so boric acid might be a good choice here. The net effect of the nuclear reaction, then, is to turn cold boric acid into hot boric acid. Then there are already terrestrial organisms which survive on reactions which exploit temperature gradients like those found at hydrothermal vents: the organism could either exploit those reactions themselves, or live in symbiosis with a bacteria that did.

In short, while you're unlikely to see an organism evolve to set up the highly unstable, low-entropy, complicated arrangement of materials that humans would consider to be "a fission reactor", fission is an energy-releasing process, and an organism evolved to harness that process in a more relaxed, stream-like, organic way, is perfectly possible.

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    $\begingroup$ There's almost no difference chemically between isotopes of one element. It's mostly in the speed of reaction, and when looking at heavy elements (like you need for fission) the difference in mass of two isotopes is so small as to have no measurable impact on chemical reaction speed. It's most noticeable for hydrogen isotopes. $\endgroup$
    – JRE
    Jan 14 '20 at 15:29
  • $\begingroup$ A fission chain reaction takes a minimum mass (or density) of fissile material. Think "kilograms" for any typical fissile material. $\endgroup$
    – JRE
    Jan 14 '20 at 15:30
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    $\begingroup$ Which is precisely why I said a reactor using a fission chain reaction was unlikely. Using the natural decay of radioactive isotopes (which they will continue to do according to their half-life whether provoked by neutron capture or not) is much more plausible. Think an atomic battery rather than a fission reactor. $\endgroup$
    – Stephen
    Jan 14 '20 at 16:20
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    $\begingroup$ Hurray! We have Godzilla! $\endgroup$ Jan 16 '20 at 16:33
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Well, first let's see what the creature has to have.

  1. A sizable chunk of Uranium. After all, you can't have fission without fissionable materials. Unfortunately for your animal, Uranium is not very common, meaning that your biological reactors would be restricted to places like Utah's Factory Butte, where there are (reasonably) large amounts of Uranium on the surface.

  2. Some way to safely process Uranium. While it is possible to process Uranium without a complex lab, it is extremely likely to cause irradiation of tissues, which is no bueno for your creature. The only reasonable way around this is to have an "access port," in which people can dump preprocessed Uranium fuel rods.

  3. Radiation shielding (since you don't want the radiation killing your creature.) For this, you pretty much only have one option: your creature somehow processes lead in bulk, and then somehow cause lead deposits to build up around the "reactor core." This is almost impossible to have evolve, so you pretty much have to make your creature a GMO.

  4. Coolant systems. Not only will your reactor be producing a lot of radiation, it will also be producing huge amounts of heat. After all, that's what a reactor is supposed to do. In this case, pretty much the only option is to have your creature immerse itself in a fast-running river and then somehow ditch the heat safely. Although not as hard to evolve as radiation shielding, it would probably be another GMO feature.

  5. Using the energy. While it is possible to make the reaction core part of your creature, there is simply no way for your creature to harness the energy in any meaningful way.

All that being said, while your creature is impractical in real life, it is a very cool idea as a minor aside, and the problems can be handwaved. That being said, I very much would not give these creatures a major role in your story, as then your handwavium would break down.

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    $\begingroup$ So no way to make Godzilla even remotely plausible? $\endgroup$ Jan 16 '20 at 16:32
  • $\begingroup$ @JacobBlaustein Unless you want to make it a Japanese experiment that has gotten out of control, no. $\endgroup$
    – The Daleks
    Jan 16 '20 at 17:10
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even if it is an old question, but surprisingly I do not see yes answers.

yes, it is possible.

Surprised by nobody mentiond that Radiotrophic fungus

Radiotrophic fungi are fungi that can use radiation as an energy source to stimulate growth. Radiotrophic fungi have been found in extreme environments such as in the Chernobyl Nuclear Power Plant and on the exteriors of Low Earth orbit spacecraft.

Most known radiotrophic fungi utilize melanin in some capacity to survive.2 The process of using radiation and melanin for energy has been termed radiosynthesis, and is thought to be analogous to anaerobic respiration.

There quite a lot on the topic on the internet, one of the uses bioremediation of different radioactive polluted places.

Sure fungi isn't that much of a nuclear reactor but it shows that biological systems can convert nuclear energy and incorporate it into their biological cycle.

Fungi is one of the primitive forms of life, and if we like to have naturally evolved nuclear reactors, then certain conditions for their evolution have to be met, and those fungi are like 2-3billion years in the past - a starting point for such evolution.

Steam and high pressure are not the only ways to extract nuclear energy - gamma radiation is the same electromagnetic photon as light, so alpha and beta particles can be used as well, as charge carriers, and we have life's which uses electricity more than usually - electric eel's - meaning biology can handle electricity.

Biological life can build constructions, let's say Great Barrier Reef as a prominent example - so there can be some processes, evolved ones, which may help biological life to offset some of its weaknesses.

So as result there can be different shapes ways and forms of biological life to utilize nuclear energy. A block of wood as an example is a typical carbon rods moderator for a reactor, and released hydrogen can be reused by that life as an energy source again, binding carbon and develop structure further - grow. Also do not forget there are other processes involved in petrification as an example - so it can help create all sort of weird systems and solutions.

The biggest natural evolution hurdle is in those radioactive elements, they aren't a stable and steady source of energy overtimes the evolution takes place - but there are cosmic probabilities and strange things happening out there on a great scale - some neutron source/wind can be a source of radioactive dust constantly landing on a planet, sooo...

Artificial ones - here we can run wild - sure it won't be the same as reactors we build with technology means, but there is a variety of potential designs, even if I have a hard time to imagine details or describe them, it needs to really dive in that stuff. But would be fun to have something like Slime Mold to moderate the reaction(it can insert and retract its body parts, which are water carbon moderators, in some weird shapes in some porous media to optimize the output)

here it is quite a yellow title Scientists Used Slime Mold To Create The Most Efficient Traffic Map For The United States, worth a look, those slimes funny and were used in different scientific researches as it has interesting optimization mechanisms/properties.

So the answer is yes, but how useful it may be, that's a different subject.

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  • $\begingroup$ I was about to make an answer about radiotrophic fungi too. +1 $\endgroup$ Mar 4 at 5:23
  • $\begingroup$ @John u really have some strange perception of energy, nuclear decay is always net positive, it happens on its own. what do we do in a typical nuclear reactor is climbing a mountain - on one side of that mountain is a reaction we can manage/regulate, on another side of it there is a bang - the goal is to be close to the top as possible because then energy release is faster, but do not cross it. Heat isn't the only way, watch that - the energy here can be consumed - hydrogen, visible light, gamma radiation. similar thing can be created by bio. $\endgroup$
    – MolbOrg
    Mar 4 at 11:14
  • $\begingroup$ @meaninglessname sorry, lol, but i left many points not highlighted, as John points out, so. but yeah, no that many free internet points to be earned here $\endgroup$
    – MolbOrg
    Mar 4 at 11:16
  • $\begingroup$ @MolbOrg right, I am thinking of fusion. $\endgroup$
    – John
    Mar 4 at 14:40
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    $\begingroup$ I too thought of the fungi but the problem is they aren't themselves operating internal fission reactions even on a molecular scale. True they harness radioactive particles for growth but the source is external. Not internal. The process is analogous to photosynthesis which relies on an external energy source to power the production of complex molecules. So these fungi effectively 'bask' in the emitted radiation like plants. They don't 'absorb' radioactive elements and the concentrate them in organelles or whatever to form 'micro reactors'. They don't need to. $\endgroup$
    – Mon
    Mar 25 at 6:14
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Yes but the conditions don't exist on Earth to make this a viable survival strategy for a complex multicellular organism that could produce a sustain nuclear reaction.

But let's assume your in a far off imaginary planet filled with wonder and horror, what environmental conditions would be required to facilitate the evolution of this kind of organism?

Firstly you would need an environment that has plenty of easily fissile material. Current Earth-like levels of fissile material such as Uranium 235 simply would not be enough for a big enough ecosystem for significant amounts of enrichment to occur to facilitate the development of an organic nuclear reactor.

Next you would need environmental pressures that would not only incentivise the organism taking up harmful radioactive material into their cells but also be competitive with other organisms using alternative energy sources. Remember evolution does not care what is possible, only what is successful. Therefore if these radiosynthetic organisms can't compete with other sources of energy then it will be unable evolve into a complex multicellular organism that could facilitate sustained nuclear fission. This means that the environment that this organism evolves in will likely be cold with little available solar energy. This is almost required as it would ensure that this organism could outcompete other potential organisms.

And finally you would would need lots of time which means the environment must be relatively stable. Something that might be a bit difficult when you consider that there will be literally nuclear bombs being formed en masse by these developing organisms. A poorly placed/timed nuclear detonation might outright kill the local ecosystem, something that might be a little counterproductive for the process of evolution.

But let's say that this process doesn't eradicate all life on this planetoid. Eventually as the survivors of the million year strong nuclear winter will have crawled out from their holes they would of hopefully developed ways to avoid death by spontaneous nuclear detonation. And maybe....just maybe they would have even developed ways to have sustained nuclear fission occuring in their core to take advantage of this wonderful energy source. Huzzah!

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  • $\begingroup$ "spontaneous nuclear detonation" - there almost no ways for that. "This is almost required as it would ensure that this organism could outcompete other potential organisms" - they do not have to, they need to be more successful than other alternatives in this very specific environment. Meaning - trees in a forest suppress grass, but not moss, moss does not exactly try to outcompete trees. they take their niche. An abundance of radioactive materials - by itself may and will be a suppressing factor for those who do not use it, another evolution pressure, no matter is there a light or not. 3/5 $\endgroup$
    – MolbOrg
    Mar 28 at 13:40
  • $\begingroup$ No way to achieve spontaneous nuclear detonation? I will admit that I used the wrong terminology but achieving critical mass with a huge mass of uranium 225 is entirely plausible. Then all it takes is a single neutron........ $\endgroup$
    – Jimmy
    Mar 28 at 20:44
  • $\begingroup$ U235. With critical mass alone it melts sooner than explodes, i mean it isn't that easy. And with organic materials around it will be even harder, but here it depends on particular details and overal picture or desighn which may evolve and it can take all sorts of shapes or evolved details $\endgroup$
    – MolbOrg
    Mar 29 at 1:41
  • $\begingroup$ Well your probably right, here I was imagining that this organism would be a good little boy $\endgroup$
    – Jimmy
    Mar 29 at 5:53

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