Eli5: Why is it so hard for a country to make a nuclear bomb?

Question

I’m assuming the science of making one is out there. Why then countries like Iran who so want to develop atomic weapons haven’t been able to do so?

In: Physics

Answer 1

Several reasons:

1. Obtaining sufficient fissile material is very hard. It takes a large scale industrial operation. You are either:

Refining enough Uranium 235 or manufacturing enough plutonium through a nuclear reactor. Either way requires enormous industrial capacity and cannot be easily hidden. Which brings us to reason 2:

2. everyone is watching. You can’t hide it. Countries have tried. . .but really, it’s impossible to hide the production of it. And the pursuit of it is so destabilizing, that a country risks everything from soured relations, to sanctions to attacks on its facilities if it pursues it.

3. A uranium bomb is relatively simple to engineer, but a plutonium weapon is very complex. A uranium weapon can be created by firing a plug at sufficient speed into a sphere of uranium to create a critical mass. A plutonium weapon would fizzle if you tried this. So the only way to make plutonium to go boom, is to implode it. That is a highly highly highly complex engineering challenge and while countries can figure it out, it’s among the most closely guarded secrets and takes a massive effort to develop – again, one which is not easily hidden from the world.

The nuclear club is pretty small considering the power of the weapon that it gives states, and the reason for this is, it’s hard to do, impossible to hide, incurs significant downsides in terms of becoming a threat on the world scene, and at the end of the day isn’t very useful in part because, you’ll never be able to actually use it, only threaten to use it.

Any country that actually used a weapon in an act of war would pretty much be instantly vaporized. Because as hard as atomic weapons are to make, we have thermonuclear weapons that can destroy entire large cities and be delivered anywhere on the planet via ICBMs in about 1/2 from issuing launch codes, and those are 100x as hard to make.

And even the threat of using it could easily prompt a pre-emptive strike. Atomic weapons are among the least useful tactical weapons and to get strategic importance it’s basically impossible short of being one of the great powers in the world. So, for vast majority of states, it’s just bad to pursue, costs enormous resources and creates enormous instabilities, and gains very little in terms of security.