Why is it so hard to replicate the bulding of a nuclear bomb and why only a small amount of countires have them?
In: Engineering
You need weapons grade nuclear materials in large enough quantities for them which require a lot of expensive infrastructure. Countries that have nukes do not want more countries to get them so they do anything they can to prevent other countries from building that infrastructure which can include sanctions or outright sabotage.
The countries that have production capabilities for those materials keep track of everything and have regular inspections that make it very difficult for those materials to get lost and used by those who are not supposed to use them.
The reason only a small number of countries have them is because there are international treaties limiting who can have nuclear weapons.
I don’t know anything about building nuclear bombs, but I think the problem isn’t necessarily the “know how”, it’s the ability to obtain enough quality fissile material in usable form
Edit: clarification
Many simply don’t have the resources to build them: money, expertise, natural resources, supply chains, equipment. It’s not exactly something you can do in secret either and most countries don’t want to risk becoming a pariah state.
Few countries have them because of non proliferation treaties, not wanting to become a pariah, and most simply don’t need them. For the vast majority of countries the cost of creating and maintaining these weapons isn’t worth it especially when they have a much stronger military ally who already has them.
Most countries agree that nukes are terrible, and have signed various agreements about not trying to make or sell them.
Making fissile materials is also very difficult. No matter which material you decide to go with, it’s mixed with chemically identical materials that need to be removed. Chemistry alone can’t deal with this. The most reasonable way to do this is by chemically refining the starting materials (which are both toxic and radioactive) as far as possible, chemically converting them into a liquid or gas, and then centrifuging everything. In the centrifuge, you get a tiny gradient of the heavier isotope near the perimeter and the lighter one near the center. So you separate them and centrifuge the fraction you want again. And again, and again, and again. And it never becomes pure, just more enriched. This is the kind of setup you’ll need: [https://qph.cf2.quoracdn.net/main-qimg-486c0358b869e02f4515073313aabe7c](https://qph.cf2.quoracdn.net/main-qimg-486c0358b869e02f4515073313aabe7c)
The building isn’t so much the problem as is getting the material.
You need highly specialized equipment, very dangerous chemicals, a lot of electricity, a lot of uranium ore, and a significant amount of time to separate out the U235 needed for just one basic bomb.
A basic gun design will get you in the game, but then you need to figure out how you’re going to deliver the weapon. Dropping it means you need an airforce capable of getting to your enemy whereas missles are more technologically challenging.
There are several elements to it.
First, you need to decide which version of a nuclear bomb you want to build. We’ll leave fusion bombs off the list for now, because you have to master at least one of the other types of nuclear weapons to build a fusion bomb (fusion bombs require a fission bomb to create the conditions for fusion).
The simplest type of nuclear warhead is called a gun-type bomb. These are actually rather simple to construct: You just need two sub-critical masses of Uranium-235, enriched to very high purity. Load them into a bomb container, separated by some distance. Fire one mass at the other at high velocity, and provided you have a large enough mass and velocity, it will start a chain reaction and give you a nuclear weapon. This is the type of warhead that was dropped on Hiroshima.
The problem with a gun-type warhead is the two masses of U-235. The weapon itself is simple, but refining your sub-critical masses is very hard. You need quite a large amount of it, and regular uranium is mostly Uranium-238, which can’t be used to make a bomb. And since both isotopes of uranium are chemically identical, the only way to refine them is to take advantage of the small difference in mass to separate U-235 from U-238. It’s easier to do these days thanks to high-strength centrifuges, but it’s still not something you can just do on a whim.
The other type of nuclear bomb is called an implosion-type bomb. This type of bomb uses a plutonium mass, which is carefully built into a perfect sphere whose density is just below critical density. It’s then surrounded by explosive lenses, which are carefully timed to detonate at exactly the same time. The resulting explosion then compresses the plutonium enough to cause it to go critical, giving you a nuclear explosion. This is what was detonated in the Trinity test, and also what was dropped on Nagasaki.
Getting the plutonium is much easier than U-235, because plutonium is one of the natural decay products from a fission reactor, and the isotope that’s created is suitable for a nuclear weapon. Separating it out from the nuclear waste is simple since it’s chemically distinct from the other waste products. However, building a proper explosive lens is much more difficult, and even the slightest misalignment will give you a fizzle instead of a proper nuclear bomb.
In short: No matter what, you need to do some sophisticated engineering of extreme precision in order to build a nuclear bomb. The countries that have managed it have all either developed or were given a number of tricks and refinements that either lowered the amount of fissile material requires or made it easier to construct the lensing effect necessary for the fission reaction. Most countries were given the secrets or stole them from other countries in order to manufacture their bombs; developing them from the ground up requires engineering skills that are difficult to find.
Its not that difficult. Even North Korea managed to do it. But first of all most country dont want nuclear weapons and even more so dont want other countries to get them and the best way to encourage not more countries to get them is to also stay out. Then there are international treaties that ban the development of nukes if you dont already have them. Another things is that you cant realy do it without other countries noticing that you are doing it and they will do a lot to stop you. In the case of Iran you can read about Stuxnet if you want to see how sabotage happend in reallife to stop Iran from devloping nuclear weapons.
So in short you have to very desperate to even think about it and then be fine with getting very isolated from the rest of the world. Engineering wise a lot of nations around the world can do it.
Whilst the bomb itself is complicated (even though the concept is just squeezing some enriched uranium / plutonium really hard), an obtaining uranium isn’t that difficult. The biggest obstacle is enriching nuclear materials. To do this at the kind of scale required for a functional bomb you need to put huge amounts of time money and energy into specialist equipment (that a foreign country who doesn’t want you to have nukes wont sell to you) such as centrifuges designed for nuclear enrichment.
This kind of investment is only viable in large countries (russia) rich countries (like the UK and France) or both (The USA) their is the outlier to this North Korea but that is only because most of the countries budget goes towards the military. For most countries, the costs of developing nukes far outweigh the benefits they would get, and it is far better to just ally yourself with a larger country that does have nukes.
The hard part is getting the uranium or plutonium to make the bomb. It needs to be very pure and the machines capable to doing that are so hard to make that only a few countries on earth have the capability to make those machines and they are very picky on who they let have them.
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