Alright so let’s say that we have a massive dragon about 2 miles long. This big guy needs a lot of fuel to power himself and since there is only so much food he can eat at one time, he decides to run on nuclear power. Now dragons (in this universe) utilize metals in large quantities for various purposes such as in their scales, bones, claws, etc. So this gigantic dragon goes and munches on some radioactive metals and stores them in a special organ that is immune to the effects of the radiation. The dragon then uses the energy for heat, to generate electric currents, and generally keep itself alive.

So here is the actual question. Would the above exposition (eating radioactive material), be a sufficient explanation for a radiation based breath attack? Bonus points if anyone can devise a way for said breath attack to use alpha, beta, and gamma radiation. More bonus points for anyone who could describe the effects of such an attack.

P.S. - I know that I can make this creature do whatever I want, as I’m the one writing it and “it’s a dragon.” However, I would like to have some sort of plausible explanation for its incredible abilities other than the standard “it’s a dragon and can do what it wants.”

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    $\begingroup$ I will point out that a two mile dragon will encounter all the usual problems a creature that size would; no materials strong enough to allow it mobility, sinking into the ground with every step, flight impossible, circulatory system prohibitively difficult, etc. $\endgroup$ – jdunlop Jan 28 '19 at 16:36
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    $\begingroup$ Your animals biggest problem is how is it cooling itself, et has a ridiculously low surface area to mass ratio. since metabolics are continuous, it will really quickly warm up to the temperature of the reaction inside it. $\endgroup$ – John Jan 28 '19 at 18:29
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    $\begingroup$ If your dragon is organic then pure energy alone is not enough to sustain it for more than a short period. An organic system needs energy but it also needs a constant intake of things like protein and iron and salt and all the vitamins and electrolytes. There are nutrients animals need in their diet that they can't synthesize internally and must get from eating plants or other animals. When your dragon lives only on nuke power, it's like you living on only pure sugar. You'll be energetic until your endocrine system starts to collapse. Scurvy, diarrhea, anemia, headache, and eventually death. $\endgroup$ – Jared K Jan 28 '19 at 19:57
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    $\begingroup$ @WalterMitty: He has a breath weapon that is literally referred to as "atomic breath". I'll grant I can't guarantee it's radioactive in the sense most people mean (it definitely sets things on fire, but I'm not sure any target of it lasts long enough to determine what form of radiation might be involved), but with a name like that, why not? $\endgroup$ – ShadowRanger Jan 29 '19 at 1:21
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    $\begingroup$ @mark, a radiative cooling system is not good enough, there is a reason nuclear power plants use evaporative cooling or more often something even more extreme, Passive cooling in air is not very effective. Even normal muscles at that scale would drive its temprature over the boiling point. $\endgroup$ – John Jan 29 '19 at 5:20

If the breath attack is purely radioactive it wouldn't be a very good offensive weapon because exposure to even large doses of radiation still take a while to kill, on the order of hours or days. To get such a large amount of radiation to immediately kill you would have to generate a powerful enough reaction to require tons of shielding to keep from frying your dragon.

Alternatively, maybe the radiation breath is not instantly lethal, but strong enough to give a lethal dose to anyone not completely encased in lead armor. Radiation poisoning is a pretty horrifying way to die, I'll let you look up the full list of symptoms and effects but to name a few:

  • Nausea & vomiting
  • Skin damage from radiation burns that can lead to infection
  • White blood cell death which can make infection worse
  • Anemia from red blood cell death
  • Changes in blood chemistry
  • Internal bleeding

And of course an increased chance of cancer, leukemia, etc. If this is a world before the health effects of radiation exposure has been documented, let's say people who return from trying to slay this dragon report they saw a flash of blue light (Cherenkov radiation) and begin to die over the next few hours or days from an "unknown disease". It would definitely inspire fear in those who want to slay the dragon.

A purely radiation breath could be done by having an organ which stores radioactive material and is surrounded by shielding (your dragons can use metal in their bodies, so it could be lead or tungsten). All you need to do to release this radiation is open a hole in the shielding, working like some laboratory and medical radiation sources. To win the bonus points for using alpha, beta, and gamma, all you need to do is change the level of shielding:

Penetrating power of different types of radiation

There could be some flaps in front of the organ the dragon can use to block different types of radiation, although gamma would be used almost exclusively for its penetrating ability.

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    $\begingroup$ Also the radiation poisoning might make for a nice way of "cursing" victims/enemies that slay the dragon! $\endgroup$ – AtmosphericPrisonEscape Jan 28 '19 at 15:24
  • $\begingroup$ @AtmosphericPrisonEscape ooh that's good. Not to mention the children of those with the "curse" will likely be deformed. It would be interesting to see what society thinks of these "children of the curse" and how they treat deformities in general that aren't related to dragon incidents. $\endgroup$ – scohe001 Jan 28 '19 at 16:57
  • $\begingroup$ defenses that take a while to kill are fairly common in nature, as long as anything that attacks you dies it can evolve. $\endgroup$ – John Jan 29 '19 at 5:22
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    $\begingroup$ A decaying dragon that curse the land scape near his grave. Make it come back as a Zombie dragon and you have Ep8 Tate No Yuusha. It's not a spoil if it's not out yet. $\endgroup$ – xdtTransform Jan 29 '19 at 15:00

The simplest answer is the dragon works like a nuclear reactor, causing fission of the nuclear materials its eaten, which releases tremendous heat and abundant radiation. Normally, a nuclear reactor does this in a containment vessel (meaning the nuclear process, and its bypoducts, never leave the vessel), but the dragon's innards act like a containment vessel.

When they need to attack, the dragon simply stops regulating the process (i.e. drawing the heat off to use for energy) which builds up tremendous heat. We're talking about enough heat to make lava, such as the corium that is produced in a nuclear reactor meltdown. Mix that heat with other materials the dragon has eaten, and you have a highly toxic radioactive substance that is not easily dealt with (just standing next to corium for a few minutes will kill you). In theory, you could also build up hydrogen (caused as a byproduct of the nuclear reaction breaking down water) and have the dragon exhale it. Still pretty radioactive.

Just be sure your dragon has a ready source of coolant (like water or something else).

  • $\begingroup$ Would it work to simply exhaust the hot gasses/materials for cooling? Of course it then would have to refill them sometimes. $\endgroup$ – arc_lupus Jan 29 '19 at 9:32
  • $\begingroup$ @arc_lupus It's going to have to refill at some point anyways. This process breaks down the nuclear material $\endgroup$ – Machavity Jan 29 '19 at 13:10

General Dragon Thoughts

Eating radioactive material is sufficient explanation for a radioactive breath attack, for the simple reason that vomiting radioactive debris at someone is legitimately lethal.

One difficulty to consider is that highly radioactive material is rare in nature (such material decays away quickly on geological timescales), so the dragon will perhaps struggle to get enough material or be strongly tied to a particular deposit that does contain sufficient concentrations of fissile material.

A second difficulty is how, biologically, to get value from radioactive materials. Heat is one thing, but what you really need is a way to do chemistry and manipulate the complex molecules that compose a living organism. You'd be looking for a semi-photosynthetic system that can capture the energy of gamma, beta and alpha radiation in wave modes and broken bonds of organic molecules.

Breath Attack Specifics

Radiation is not good at immediately killing things in the way that, say, being on fire is. Extreme radiation doses that shred up your molecular machinery still take about an hour for the body to get to a sufficiently bad state that it dies. Less extreme, garden-variety radiation sickness kills over a few weeks.

Regardless, the dragon could happily vomit radioactive debris from its internal stockpile at people, and if it were sufficiently dirty material they would die over the next week or so.

Or, if the dragon has an internal organ that is running a nuclear reaction, you could arrange that organ such that it can be opened/moved to a direct line of sight to the outside world (eg. organ is on the gullet, like a throat pouch, and dragon can open their mouth, flex the pouch, then BOOM, anyone in front of the dragon is staring at an exposed nuclear reactor and taking a hideous dose of gamma & beta radiation)

  • $\begingroup$ of course the dragon will not need much material, the energy density combined with the efficiency of biological systems. nuclear material is 10,000's of times more energy dense than the best biological fuels. $\endgroup$ – John Jan 28 '19 at 18:06
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    $\begingroup$ Refined nuclear fuel yes, natural nuclear ores not really. Humans eat about 2000 kcal a day, which is roughly 97 Watts of continuous power. We are, not coincidentally, warm to the touch. You will not find naturally occurring radioactive rocks hot to the touch as they are a low-energy density material. The dragon would need to eat an incredible volume of rocks to distill out the isotopes that could power an internal reactor. $\endgroup$ – Mark_Anderson Jan 28 '19 at 18:17
  • $\begingroup$ Not as much as you think, metabolic efficiency is not constant it scales positively with mass, an organism 100 times the mass only consumes 32 times as much energy. We don't know if it is an chain reaction or not. $\endgroup$ – John Jan 28 '19 at 18:28
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    $\begingroup$ This is the better answer. It is much more efficient to vomit materials like polonium on relatively low quantities, than to try to directly attack the target with external radiation. (that is easily blocked ny distance and even weakened by air.) $\endgroup$ – b.Lorenz Jan 28 '19 at 19:40
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    $\begingroup$ (The Gabon reactor was possible because Uranium deposits were significantly richer in early years of the African Craton. U235 has a sub-billion year half-life. Present day deposits are too poor to achieve the natural fission. A young world might make a lot of sense for the dragon though, the crust will be significantly enriched in radioactive product compared to what we are used to ) $\endgroup$ – Mark_Anderson Jan 28 '19 at 22:34

The other answers are good in general. Let me propose a somewhat specific way of bringing this about.

The dragon indeed has a running nuclear rector in its belly. (Look at NASA's Kilopower project to see how (relatively) small and simple a reactor can be (your dragon needs way bigger))) It uses the temperature difference between its core and the wings (rejecting heat and having many vessels for coolant-blood) to produce power. This produces mechanical or electrical power (lets say in pistons or in termoelectric converters) Radiothropic symbionts complement this, allowing direct production of organics for the "meaty parts" of the creature.

The reactor has thick shielding/neutron reflectors in the most directions, except downward. This acts as a secondary weapon (irradiates things upon flyby), but has an another useful effect. When the dragon finds an uranium ore deposit, it digs in or finds a cave, and sleeps on a floor of nuclear ore. The leaking fast neutrons effectively turn the dungeon floor into the breeding zone of a fast breeder reactor. Naturally abundant U-238 (fertile but unfissile) is converted into fissile Pu-239. After that the dragon can eat already highly fissionable material, reducing the processing is has to perform internally. (Still needs chemical processing, but little or no isotope separation) The main radioactive weapon is the byproduct of this. Highly beta and alpha active daughter elements remain back, and get separated when the dragon secretes the reactor fuel from the ingested material. These get mixed (perhaps in form of salts) into water, and emitted as a plume of either boiling water or steam. On the effects likely for an unfortunate knight who inhales, ingests or gets contaminated by this, see the fate of Litvinenko

And the dragon has one last nasty trick. It can poop highly radioactive spent fuel elements when they became depleted (or poisoned by reactor poisons). These are used to reinforce the dragons liar with a many-miles wide dirty perimeter, making even approaching it nigh suicidal.

  • $\begingroup$ This is good stuff. $\endgroup$ – Mark_Anderson Jan 28 '19 at 22:38
  • $\begingroup$ Love the idea of using its stomach to activate uranium deposits. +1 $\endgroup$ – Bewilderer Jan 29 '19 at 3:17

Lets start by making this a fission based dragon vs a fusion based dragon so the dragon will have a use for eating all that radioactive material.

Since the dragon will not be able to use uranium ore directly there will need to be a few steps in its digestion process. The first step will be to grind up the ore by chewing and dissolve the uranium ore "yellowcake" in nitric acid in the dragon's stomach to form uranyl nitrate. Then the uranyl nitrate will be passed to the dragon's second stomach where it will be combined with ammonia to create ammonium diuranate. The dragons third stomach will reduce the ammonium diuranate with hydrogen to get uranium dioxide while its 4th stomach will convert that with hydrofluoric acid to uranium tetrafluoride before its 5th stomach oxidizes the results to get uranium hexafluoride "hex".

Once the food is digested it will have to be enriched and molded into a useable form. The hex will be passed via a special organ in the dragon's body consisting of a huge chain of diffusion chambers used to separate the uranium-238 from the uranium-235. The Uranium hexafluoride gas will be cascaded through the diffusion chambers before being passed to the dragon's 6th stomach that chemically removes the fluoride from the hex and transforms it into Uranium dioxide. The Uranium dioxide is then melted and compressed into pellets that are stored in the dragon's reaction chamber.

The dragon's reaction chamber holds the enriched Uranium dioxide pellets close enough to achieve criticality when moderated by the high-pressure water running through it. The high-pressure water is used as both a moderator to keep the reaction critical and as the coolant used to move the energy in the form of heat throughout the dragon's body to its cooling organ, its skin.

Each scale on the dragon has a copper inner side and a steel outer side. The temperature differential between the outside atmosphere and the high temperature, high-pressure coolant water works as a thermocouple to simultaneously cool down the dragon and generate electricity. This electricity is what is used to power the exotic dragon musculature that allows these majestic creatures to hold their immense two-kilometer bodies aloft without being crushed under their own weight.

The dragons breath weapon is powered by pellets generated in its reaction chamber and moved up the dragons esophagus to its breath chamber. When it wants to rain down death on its foes the dragon moves the pellets in its breath chamber together at the same time it opens its mouth and feeds chunks of waste u-238 into its breath chamber. The extreme heat from the breath chamber reaction turns the uranium into a stream of high velocity extremely radioactive uranium plasma.

  • $\begingroup$ uranium refinement/enrichment/compression as Draconic digestion, love it! $\endgroup$ – sam boosalis Feb 28 '20 at 0:19
  • $\begingroup$ Re the time multiple stomachs: the diffusion chambers and 6th(?) stomach sound like small and large intestines. $\endgroup$ – sam boosalis Feb 28 '20 at 0:21

One issue that I see is that if it's a flying dragon maybe being 2 miles long strains the imagination somewhat. Also, there are not many materials sturdy enough for such a large object to be made. For instance bones are pretty close to the limit with something like an elephant. If it's 2 miles long, what are its legs made of? How does it not sink into the ground?

With regards to storing the radiation, the problem is shielding. Alpha and beta are trivial to shield against. Even a paper sheet will do. Gamma is a lot harder. To stop those, you need a lot of matter, and it has to be something dense, like lead. Now you have the issue of this thing moving around with the weight of the reactor and the shield. In fact, the closest thing to what you describe is a modern aircraft carrier, which is pretty much only possible on water. Maybe it should be a water dragon.

Second, the part about the breath weapon. First of all, the dragon need not breathe, but can simply store quantities of radioactive fuel somewhere like above its eyes, and have dangerous "heat vision". You can make the aperture out of lead bearing proteins or whatever (actually, it really has to be a solid lead, any protein with lead co-factor would have way too much gamma-transparent non-lead, so you would need A LOT of the shielding, like dozens of meters thick probably). Second, in reality a lot of the danger of nuclear bombs is not the explosion. That's gone in an instant. What happens though is a lot of radioactive dust is generated. You breathe/drink/eat this dust and then it shines radiation on the inside of your lungs, which is how you get cancer. The breath sounds like it has radioactive dust in it. So how would it avoid breathing this dust itself? Spitting a solution of radioactive dust would be more believable. Also, as others point out, it wouldn't be an instant effect. So perhaps it makes more sense for the dragon to breathe superhot steam from the reactor cooler, or plasma (for instance, directly from the reactor if it's a fusion dragon).

Fusion dragon would also be nicer because the fuel is just hydrogen, easier to find than Uranium ore. Also, ore actually has a tiny amount of active isotope. Tiny amounts of it must be filtered from huge quantities of ore. This is done with a centrifuge, because a slight difference in mass is really the only way to distinguish the two isotopes, they are otherwise chemically identical. So your dragon must eat A LOT of these rocks (how???) to get enough fuel, even if he located a nice exposed uranium vein. And it won't be easy for his cells to chemically enrich it, he'd need a centrifuge organ (???) or something equivalent. It's also pretty incredible that you could biochemically enrich uranium, because it's so hard for living cells to distinguish isotopes that whole experimental methods are based around it. I'm not aware of a single conclusive case where a biological system could meaningfully distinguish isotopes.

I think however you always have the option of simply not dealing with any of this. Just declare that the dragon's biology is radically different and much less vulnerable to radiation. Maybe it doesn't have DNA but entirely different biochemistry. Maybe it has exceptional mutation tolerance. Maybe its immune system is really good at fighting cancer. Who knows, I mean, it's a 2 mile animal, it's clearly nothing like any living creature we know.

And lastly, the dragon's breath doesn't have to actually be deadly. A creature like this sounds like bad news, I wouldn't want to mess with it. So I bet a lot of information about its weapons is 2nd, 3rd and 4th hand. It's rumor and legend. Perhaps the dragon's breath doesn't instantly kill, but after he attacks the crops die and children are born malformed for decades, such that the town is eradicated. Over many retellings, this time aspect gets blurred, and people start thinking that the dragon just breathed once and everyone instantly turned into mutants. Not like many people would track him down to try and see for themselves.


Actually a radioactive breath would be an extremely useful tool for a behemoth 2 miles long slowly plowing trough the surface. You would effectively need siege weapons to do anything to it and those take hours to days to build. A synced timescale with radiation death.

Another thing what could HUGELY increase the effect and danger is if he could breathe out clouds of radioactive dust. That is real nasty. Just irradiating someone is unpleasant. Ingesting that radiation in lungs is deadly quite fast. Also would serve as a simple probe for radiation, because if it breaths the stuff on some plants and they don't die, it is possible that there is heightened radiation source in the ground.... Lunch time!

Also at such scale you would have to think about a totally different organisation level. As was stated, cooling, circulation and movement will be difficult in the traditional sense. So huge wings will be probably used just for cooling (or scales, protrusions, shields), but generally you could take some inspiration in ship design or building design.

Or if you want to want to be a little ridiculous, you could make it generate super-heated plasma and use it as a propellant. Kinda like a rocket. And That could be used immediately like a kind of breath weapon....... Or maybe air-based catapult.

  • $\begingroup$ So you propose a dragon firing a nuclear ramjet? :)) en.wikipedia.org/wiki/Project_Pluto $\endgroup$ – b.Lorenz Jan 28 '19 at 19:42
  • $\begingroup$ :D Did not think that far. More in the direction of a 2-mile frog. Hopping form crater to crater.... there would always be a crater on both ends :D $\endgroup$ – Selenor Jan 29 '19 at 13:25

Particle beam shooting radiochemistry doing superentity.

  1. Giant dragon is a colonial organism of specialized beings - a tight swarm or flock rather than a single 2 mile entity. It can spread or shrink according to need. Certain parts might remain earthbound or largely subterranean except in times of need. This sidesteps giant creature impracticalities but allows the thing to become a de facto giant creature when that morph is necessary.

  2. The radiant energy from the isotopes it eats are used for energy capture photochemistry in a manner analogous to how plants capture visible light radiation with photochemistry.

  3. The breath weapon is not radiant energy. It is a particle beam of radon. Radon is the byproduct of the dragons isotope food and radon particles would make an excellent particle beam as laid out here: What subatomic particle is best for a particle accelerator gun? The particles are accelerated by specialized organisms which generate electrical current and a consequent magnetic channel that accelerates the radon ion. A beam of radon ions in an atmosphere would become a channel of plasma and flame as it progressed, with the energetic radon particles dumping their energy into gas particles they encounter, ionizing some molecules to hot plasma and heating the mass to incandescence. Solid matter hit at short range by the particles would also be ionized and heated in a cascading chain reaction. At farther distances, heating by the hot gas and plasma would be more relevant.

Probably the subentities within the dragon which are responsible for storing radon would be killed in the course of a breath weapon activation - a being like this will have lots of available energy but depletion of the radon subentities / radon supply will limit the number of times it can use that weapon.


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