Producing Uranium for Peaceful vs Weapon Use: Explained

[nukeman]

Hey guys,

Can someone explain to me, in a physics/scientific way, the keys differences on what it takes to produce uranium for a nuclear reactor, compared to producing uranium for a Nuclear weapon?

Also, when you have the 2 finished products (reactor grade uranium vs weapons grade uranium, what is the difference in terms of the physics and chemistry of the material?

Or any helpfull links to some info regarding this would also be great.

?

Cheers :)

 

[K^2]

Purity and quantity are the main differences. Weapons grade uranium needs to be more pure, so you need to have more centrifuge stages. While for reactors, you usually go for quantity, so you have more centrifuges per stage with fewer stages. That's how you can usually tell if the facility is geared towards weapons grade or reactor grade by looking at the way centrifuges are arranged.

 

[nukeman]

Purity and quantity are the main differences. Weapons grade uranium needs to be more pure, so you need to have more centrifuge stages. While for reactors, you usually go for quantity, so you have more centrifuges per stage with fewer stages. That's how you can usually tell if the facility is geared towards weapons grade or reactor grade by looking at the way centrifuges are arranged.

Hey Thanks!

Do you possibly know any links that better explain what you said on how centrifuges are arranged? Or more details on the process and differences of the processes that enrich both reactor grade and weapons grade?

On the difference in the chemistry/physics of the material, I am mainly looking for specific numbers of the differences.

Again, much thankS!

 

[mathman]

The basic difference between reactor grade and weapons grade is the fraction of U235.

http://en.wikipedia.org/wiki/Enriched_uranium

The above gives all the details. Note that reactor grade is a few %, while weapon grade is ~ 90%.

 

[nukeman]

The basic difference between reactor grade and weapons grade is the fraction of U235.

http://en.wikipedia.org/wiki/Enriched_uranium

The above gives all the details. Note that reactor grade is a few %, while weapon grade is ~ 90%.

Great thanks, tons of info there!

Does anyone know what makes a US nuclear war head, which is VERY small, have a yield of around 300 to 500 kilotons, while let's say a new country makes a first nuclear bomb, its the size of a truck, and have small yield of like 20+ kilotons?

Is it the uranium it self, weapon design or added elements such as tritium?

 

[K^2]

Does anyone know what makes a US nuclear war head, which is VERY small, have a yield of around 300 to 500 kilotons, while let's say a new country makes a first nuclear bomb, its the size of a truck, and have small yield of like 20+ kilotons?

These warheads are plutonium, not uranium, and they are fusion-boosted.

Simplest A-bomb you can build is a gun-type, where the fuel is split between a "bullet" and "target". The "bullet" is fired into the "target", the combined mass is over the critical limit, and you get an explosion. This is the type of bomb that was dropped on Hiroshima.

Plutonium bombs are implosion-type. That means that a plutonium sphere is enclosed in depleted uranium shell, and then a spherical explosion from outside compresses the whole thing to the point where plutonium crosses critical mass. These designs can go a bit higher with very good detonation, but not significantly so. Nagasaki was bombed with one of these.

Finally, when you want to get a yield in hundreds of kT, what you do is you boost the bomb with tritium. In modern devices, there is a void in the middle of the plutonium sphere filled with Lithium Hydride compound. Specifically, it's Li-6 and H-2, which is why it's more commonly known as Lithium Deuteride. When Li-6 is struck by neutrons from fission in plutonium, it can decompose into Helium and H-3, or Tritium. Tritium fuses with deuterium to produce another Helium nucleus and a neutron, releasing an absurd amount of energy.

If you need to go past half a megaton, however, you need a lot more lithium deuteride than you can store in the plutonium shell. In that case, primary implosion bomb, usually also boosted, is used to "light" the secondary that consists of a large quantity of lithium deuteride enclosed in uranium. This is known as Teller-Ulam device, and that's your typical H-bomb. Ivy Mike was this type of device at 10MT. So was Soviet Tzar Bomb that yielded 50MT. All of the modern warheads in 1MT+ range are smaller versions of this design.

 

[nukeman]

K^2, fantastic, just what I was looking for.

Curious, let's say a country, like...Iran, is trying to make a nuclear bomb. They are already at the stage where they can make reactor grade uranium...

What would be a typical first bomb that a country like Iran would try to make? Would it be a gun-type, or go right for a plutonium implosion device?

 

[K^2]

I can't really tell based on anything I know. One might be more likely than another, but the way I see it, either one can be done sneakily and either one will take time. To build uranium bomb, they'd have to make sure their facilities can produce weapon grade uranium. That's a bit tricky to do without being caught. Same deal with plutonium bomb, though. To get plutonium, they'd have breeder reactors, and there are some tell-tale signs that reactor is built to generate plutonium rather than to provide power. I mean, it will always do both, but it can be geared towards one or another.

So I don't know which they'll go with, but in either case, I wouldn't expect them to build anything in excess of 20-50kT for the time being. It will take them decades to build reliable fusion-boosted devices. And to be honest, I don't see why we don't just let them. There is no way they'll get sufficient arsenal to do any serious damage to anyone in foreseeable future, and any nuclear attack on their part would be answered with complete and total annihilation. I just can't see them using the weapons. On the other hand, Israel being the only country with nukes in the region can't be a good thing. I'd see some point in keeping everyone from having nukes, but since US helped Israel get theirs, trying to prevent anyone else from having them seems irresponsible. It only serves to destabilize the region further.

 

[Astronuc]

Hey Thanks!

Do you possibly know any links that better explain what you said on how centrifuges are arranged? Or more details on the process and differences of the processes that enrich both reactor grade and weapons grade?

On the difference in the chemistry/physics of the material, I am mainly looking for specific numbers of the differences.

Again, much thankS!

Reactor grade U for LWRs is usually enriched up to 5% (by weight) in U-235, and it is manufactured in the form of ceramic UO₂, and it typically sintered to a density of 10.4 to 10.5 g/cm³. LWRs may use (U,Pu)O₂, where the mix maybe up to about 8% Pu with a fissile content equivalent to abou5 4.5% U-235.

Fast reactor fuel has a higher enrichment up to 20% U-235 by weight, but more commonly, fast reactor fuel uses fissile Pu-239/240/241. The fuel form may be MO₂, where M = U,Pu, or carbide or nitride form MC or MN.

The concern with Iran is the development of enriched uranium beyond 20%, and possibly the production of Pu-239. I will not comment on nuclear weapons design.

 

[truman]

How quickly can uranium be enriched from 20% to 80% U235 using gas centrifuges?

It seems that the time required would increase exponentially for every linear unit increase in 'purity'.

Or, it would require an exponential increase in the number of centrifuges to produce a linear purity/time relationship.

 

[nikkkom]

On the other hand, Israel being the only country with nukes in the region can't be a good thing.

Do you prefer several, including some religious fanatics?

I'd see some point in keeping everyone from having nukes, but since US helped Israel get theirs

I don't think so.
No one was helping Israelis to make their nukes. Sure, France and US were not working against it *too strongly*, but they certainly weren't willingly giving nuclear secrets to Israel.

Culturally, Jews are inclined to be educated, to study. Consequently, a lot of them are scientists. Including those who worked on Manhattan project. Some of them then emigrated to Israel. It's not a surprise Israel managed to build the bomb by itself.

Also, it looks like at the decision point many in Israeli govt hesitated to go down that path either, but eventually they decided to do it.

 

[zapperzero]

How quickly can uranium be enriched from 20% to 80% U235 using gas centrifuges

Eh? How many centrifuges? Of what type? How reliable are they? How much uranium do you have? How much are you prepared to throw away? There is much detail here, including tentative answers to some of your questions:

http://isis-online.org/isis-reports/detail/irans-gas-centrifuge-program-taking-stock/

 

[wizwom]

Any system of enrichment will take the feedstock to greater enrichment; feed back in the output, and you get more enrichment. The entropy decrease to go from ore (~0.7%) to reactor grade (~5%) is approximately the same as to go from reactor grade to weapons grade.
The Mass balance is obvious, that is, the mass of both isotopes from the feed must be present in either the tails of the product.
So
$M_F = \left(\frac{x_P-x_T}{x_F-x_T}\right)\frac{M_{25}}{x_P}$
The "value function" is
$V = (1-2x)ln\left(\frac{1-x}{x}\right)$
and the "separative work function" is
$SWU = M_P\left[V(x_P)-V(x_T)\right] - M_F\left[V(x_F)-V(x_T)\right]$

Lamarsh says the tails get to 0.2%.

Now you can do the math yourself.