Nuclear Dangers: Part 3–Qualitative Characteristics of Dirty Nuclear

world events

Chuck Shunk


October 12, 2022

The Characteristics of a Dirty Bomb

Now I want to look at the characteristics of a good “dirty bomb”, so that we can tell if a nuclear power plant would make an effective one. We want to know here, what are the dangers involved in Russia controlling Ukrainian nuclear power plants and having free reign to cause whatever mischief they want with them?

I’m going to look at three scenarios here:

  1. Constructing a dirty bomb from the highly radioactive material contained in these plants, with the goal of detonating a bomb that kills a lot of people with this radiation.

  2. Constructing a dirty bomb that doesn’t focus on killing the maximum number of people, so much as poisoning a large area with radioactive fallout.

  3. Intentionally causing a disastrous meltdown at a nuclear plant.

When considering these scenarios, I am going to ignore the danger of panic any one of these tactics would cause. This is a significant omission, but one I have to make in order to have an objective basis of comparison of harms. Just keep in mind: this analysis is very incomplete without considering the psychological impact of these actions, which would probably be considerable in each case.

Killing with instananeous amounts of external radiation

If you want to kill people quickly, the key thing to remember here is what we’ve already established: that you need a high amount of radioactivity to do damage to someone due to external radiation. Suppose you wanted to do the maximum amount of damage to as many people as possible with the initial blast of a dirty bomb; you can’t get the material inside people that way, so you need go the route of large amounts of radiation from highly radioactive material. Your goal would then be to get the most of this extremely radioactive material you could find, and then disperse it explosively over as wide an area as possible.

There are several problems with this scheme. First, the amount of radiation that will damage people is the amount of radiation per square meter of dispersion; for any particular person, the only radiation that matters is the radiation that he actually experiences where he is situated. But the radiation you can produce is related to the quantity of material you have, and so the radiation per unit of area will go down the larger the dispersion is. This means that two of your goals for the dirty bomb you are creating are diametrically opposed: the larger the bang, the more diluted it makes the radioactive fallout.

So to be effective at killing people in and around the blast area, you’ll need a tremendous amount of very radioactive material concentrated in your bomb, so that it will still be dangerous when dispersed. But this raises problems of manufacture and delivery. Suppose you had enough radioactive material that even if dispersed throughout a square mile, it would kill maybe 1 out of 10 people in the area. This material would have to be packed into the area of about a single square meter when in bomb form, and that works out to your material being about 2.5 million times as compact at this stage. If this radiation will kill 1 out of every 10 people when dispersed, what will 2 million times that radiation do to the people building and transporting the bomb?

You might think, well it could be built with very thick shielding. But, first of all, this shielding would be pretty monstrously thick and unwieldy for a portable bomb. More importantly, shielding can’t cancel out the energy–it would have to just hold it in by reflecting it back into the core of the bomb. Most assuredly, the whole thing would just melt and/or self-destruct the explosive mechanism.

But the problems get even worse! Remember that highly radioactive material is highly radioactive because it is decaying rapidly. This means that this material you chose because it emits so much radiation is also quickly becoming less radioactive, decaying exponentially. Consequently, if you want to have an effective radioactive cloud after detonation, you need build your bomb at a time in which this material is far more radioactive. And do it quickly so you don’t lose its efficacy. And somehow, don’t die while you build and deliver it.

The bottom line is, attempting to kill lots of people with deadly radiation using a dirty bomb is pretty much impossible. It is, at the least, far easier to kill more people by just getting more explosive in the first place.

Poisoning an area with harmful radioactive material instead

OK, so let’s abandon the idea of killing people with the external radiation from dispersed material. Let’s focus on poisoning them instead. Here we would shift focus to a longer, slower emitter of radiation that is absorbed by the body. There are some challenges to this, however:

First, we should recognize that we have all of the same problems described above: the bigger the blast we want, the more diluted our poison is going to be; the more material we want to deliver, the more dangerous and difficult to construct our bomb will be in the first place. These problems aren’t as fatal for this venture, but they are still problems that tend to decrease the effectiveness of our bomb.

There are additional problems for this version of the bomb. If you want to poison people with a material, you have to get it into a form that can be ingested: tiny particles that can dissolve into water and mix with the soil and be uptaken by plants. Most radioactive materials when blown up with high explosives, do not actually pulverize per se. The most common ones are metals of some sort, from which will tend to get shrapnel, not dust.

Nuclear explosions do vaporize all of their radioactive material. A nuclear explosion is so hot that everything inside the fireball is transformed to gaseous form. The radioactive fallout from the nuclear explosion forms at the edges of the fireball once it starts cooling down. Tiny metal particles condense out of the gaseous cloud; the typical size of these particles ranges from dust motes to large sand grains–all very good sizes for contaminating water and food supplies, unfortunately.

In our scenario in particular, we are looking to create a dirty bomb from material that comes from a nuclear power plant. These would be in the form of solid metal rods, containing a bunch of different radioactive elements. In order for the end result to be be particles small enough to pollute the environment and encroach your victim’s bodies via food, drink, or air, you would really need to powder the metal before you blow it up. And this again means working at close proximity to highly radioactive material for in order to process it and put it in your bomb. Really, you need remotely operated robots to do this work, and while they make such things for handling nuclear materials, I’m fairly sure they don’t make them with grinders attached, so you’ll have to figure that part out yourself.

Are dirty bombs even a realistic threat?

There are some strong arguments that the whole concept of a “dirty bomb” as a weapon of mass destruction is a dud, pure and simple. The Wikipedia article on dirty bombs references some good ones, including the U.S.NRC Fact Sheet on dirty bombs which claims dirty bombs are not weapons of mass destruction so much as weapons of “mass disruption”, and a study on dirty bombs by G. King that estimates the increase chance of cancer from a dirty bomb of expected design to be approximately equal to smoking five packs of cigarettes.

Is there a real threat of a dirty bomb in Ukraine?

The bottom line here, is that to make any sort of a decent dirty bomb, Russia would need advanced capability to process the nuclear material. Ideally, they’d separate out just the material that has the very best properties for poising people, and get it into just the right form so that it atomizes during the explosion and spreads everywhere. This is a significant engineering feat that would take advanced tools and specialized knowledge.

None of this, therefore, is something that Russia could just order some ordinary regiment occupying Zaporizhzhia to carry out by blowing up a reactor at the nuclear plant. That would create a mess, for sure, and also for sure there would be some radioactive shrapnel all around the site itself, but the nuclear release to the overall population would be minimal. Likewise, anything that could happen due to an accidental shelling would amount to some kind of nasty industrial cleanup work on site, but would be unlikely to cause any sort of mass-casualty event.

And then, even if such a thing were to be engineered, the actual harm from such a bomb is never going to be extreme. It sounds, therefore, as if harm caused by Russia engineering some kind of dirty bomb from the nuclear material it controls in Ukraine would be primarily a terror operation designed to instill panic, not something intended to actually kill a lot of people.

Characteristics of a Dirty Nuclear Meltdown: Chernobyl

So if a constructed dirty bomb is not a realistic threat (ignoring again the psychological impact), how much damage could Russia cause by (either accidentally or on purpose) by causing a nuclear meltdown? Chernobyl was a very bad nuclear accident that rendered a whole area uninhabitable; how did it do that, and could Russia (again, either accidentally or on purpose) make that happen at Zaporizhzhia?

The key thing that made Chernobyl such a disaster was not the initial meltdown and explosion: it was the fire. Chernobyl’s reactor was graphite moderated, meaning that the nuclear material was contained in a massive graphite structure. When the nuclear material melted down, the intense heat it generated actually caught the graphite on fire. Graphite doesn’t burn easily, but once it does, it creates intense heat. In addition, the roof of the reactor buildings and the turbine hall had been constructed with bitumen, which is also combustible and which also caught fire.

These raging fires were hot enough to create massive updrafts, lofting melted particles of core material far into the sky in billows of radioactive smoke, which then cooled and rained down over the a wide area. The fire is what managed to turned the core radioactive material into dangerously small particles, and what dispersed them over a large an area. Where a dirty bomb builder would have to find some way of pulverizing his material for deadly dispersion, the white-hot burning graphite did this naturally, like a radioactive thurible of death.

The graphite fires at Chernobyl were so terrible it took a full 14 days to put them all out. By the end, about 5% of the total reactor core mass was released to the environment in this way, including a full half of the iodine-131 and cesium-137 originally in the reactor.

Fast Water Reactor Meltdowns: Three Mile Island and Fukushima

The nuclear power plant at Zaporizhzhia, like the majority of power plants in operation, are “Pressurized Water Reactors” (PWR) instead, meaning that the nuclear fuel is moderated with water, not graphite. Without this graphite, could a PWR reactor fail in some similar way that would cause massive dispersion of radioactive material?

We have seen a few failures of PWR power plants, most notably Three Mile Island and Fukushima. In neither of those failures, though, was there any significant fire in the reactor core, because in a PWR reactor there is nothing to burn. In the case of a meltdown with a PWR reactor, the coolant (if any left) would boil away and the fission reactions in the core will immediately begin to slow down because of a lack of moderator. The core will still be very hot for quite a while, and can melt through the reactor vessel and into the concrete containment vessel below.

In the case of Three Mile Island, the only release at all was some radioactive noble gases release to the atmosphere from an initial explosion that cracked the top of the containment vessel–a trivial amount of radioactive material that could not possible have harmed anyone not in the very immediate vicinity at exactly the time of the release.

In the case of Fukushima, some combination of the earthquake, tsunami, and meltdown ruptured one of these containment vessels, causing a fairly large release of radioactive material in the form of sea water infiltrating the containment, dissolving some parts of the melted core, and then carrying it out with it when it leaked out again.

Because of the manner of breach of containment, while quite a bit of radioactive material was leaked from Fukushima’s Reactor 2, the impact to humans is negligible to non-existent. Material leaching into the ocean becomes dispersed very rapidly over a very large volume of water due to the continuous motion of the ocean. This is in contrast to the path of the smoke from Chernobyl, the bulk of which was deposited relatively nearby.

It is true that detectable amounts escaped into the upper atmosphere and were then discovered all over Europe, but the bulk of the material in the radioactive smoke was too heavy for such long journeys and fell all over the immediate vicinity. Remember, again, that there is a tremendous difference between detectable amounts of radiation and dangerous amounts of radiation.

Could you make a PWR reactor meltdown worse?

So it seems all but impossible for a PWR meltdown to ever get close to the kind of environmental contamination that Chernobyl created . . . I struggle to think of any scenario in which that kind of dispersion could happen without the huge fire that Chernobyl experienced, and I can’t think of any way in which this could happen under any sort of an accidental scenario, even involving things like shelling or stray explosions.

I have thought of a way in which it might be possible to engineer such a thing on purpose if you really put some time and resources into the problem–though I am not going to record the details of my theoretical plan here, on the off chance that someone with nefarious intentions ever reads this blog post!

I’m positive, though, that with my own plan, and almost certainly with any similar plan, it would be quite impossible to get away with such a thing without leaving behind very obvious evidence that the whole thing was manufactured by someone who had control of the area for a substantial time. I think this matters, because I think that a manufactured nuclear disaster caused by Russia would be much more likely if they could claim with any sort of plausibility that Ukrainian “terrorists” cased the incident.


I think it is safe to say that a disaster of Chernobyl scale is very unlikely to occur or be deliberately caused at any of the nuclear plants in Ukraine. This means we can use Chernobyl as a realistic “worst-case” scenario for any sort of nuclear disaster that Russia might cause in Ukraine–all scenarios involving accidents and most involving deliberate mischief are going to end up considerably less bad than Chernobyl. Causing a disastrous, Chernobyl-style meltdown also has a lot more potential for actual damage caused than building a separate dirty bomb from nuclear materials from a Ukrainian nuclear plant, so we can probably just ignore that scenario and focus on just the meltdown scenario going forward.

With this settled, we can finally do an apples-to-apples comparison between the magnitude of harm a nuclear bomb would cause and the magnitude of harm a worst-case nuclear disaster would produce. That will be the next blog post.